base.txt   issue38.txt 
Secure Neighbor Discovery Working J. Arkko Secure Neighbor Discovery Working J. Arkko
Group Ericsson Group Ericsson
Internet-Draft J. Kempf Internet-Draft J. Kempf
Expires: June 28, 2004 DoCoMo Communications Labs USA Expires: June 29, 2004 DoCoMo Communications Labs USA
B. Sommerfeld B. Sommerfeld
Sun Microsystems Sun Microsystems
B. Zill B. Zill
Microsoft Microsoft
P. Nikander P. Nikander
Ericsson Ericsson
December 29, 2003 December 30, 2003
SEcure Neighbor Discovery (SEND) SEcure Neighbor Discovery (SEND)
draft-ietf-send-ndopt-pre01 draft-ietf-send-ndopt-pre01
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
  Skipping to change at page 1, line 39:
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http:// The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt. www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 28, 2004. This Internet-Draft will expire on June 29, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract Abstract
IPv6 nodes use the Neighbor Discovery Protocol (NDP) to discover IPv6 nodes use the Neighbor Discovery Protocol (NDP) to discover
other nodes on the link, to determine each the link-layer addresses other nodes on the link, to determine each the link-layer addresses
of the nodes on the link, to find routers, and to maintain of the nodes on the link, to find routers, and to maintain
reachability information about the paths to active neighbors. If not reachability information about the paths to active neighbors. If not
secured, NDP is vulnerable to various attacks. This document secured, NDP is vulnerable to various attacks. This document
specifies security mechanisms for NDP. Unlike to the original NDP specifies security mechanisms for NDP. Unlike to the original NDP
specifications, these mechanisms do not make use of IPsec. specifications, these mechanisms do not make use of IPsec.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Specification of Requirements . . . . . . . . . . . 4 1.1 Specification of Requirements . . . . . . . . . . . . 4
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Neighbor and Router Discovery Overview . . . . . . . . . . 7 3. Neighbor and Router Discovery Overview . . . . . . . . . . . 7
4. Secure Neighbor Discovery Overview . . . . . . . . . . . . 10 4. Secure Neighbor Discovery Overview . . . . . . . . . . . . . 9
5. Neighbor Discovery Options . . . . . . . . . . . . . . . . 11 5. Neighbor Discovery Protocol Options . . . . . . . . . . . . 11
5.1 CGA Option . . . . . . . . . . . . . . . . . . . . . 11 5.1 CGA Option . . . . . . . . . . . . . . . . . . . . . .11
5.1.1 Processing Rules for Senders . . . . . . . . .13 5.1.1 Processing Rules for Senders . . . . . . . . . 12
5.1.2 Processing Rules for Receivers . . . . . . . .13 5.1.2 Processing Rules for Receivers . . . . . . . .13
5.1.3 Configuration . . . . . . . . . . . . . . . .14 5.1.3 Configuration . . . . . . . . . . . . . . . .14
5.2 Signature Option . . . . . . . . . . . . . . . . . . 14 5.2 Signature Option . . . . . . . . . . . . . . . . . . .14
5.2.1 Processing Rules for Senders . . . . . . . . .17 5.2.1 Processing Rules for Senders . . . . . . . . . 16
5.2.2 Processing Rules for Receivers . . . . . . . .17 5.2.2 Processing Rules for Receivers . . . . . . . .17
5.2.3 Configuration . . . . . . . . . . . . . . . .18 5.2.3 Configuration . . . . . . . . . . . . . . . .18
5.3 Timestamp and Nonce options . . . . . . . . . . . . 19 5.2.4 Performance Considerations . . . . . . . . . . 19
5.3 Timestamp and Nonce options . . . . . . . . . . . . .19
5.3.1 Timestamp Option . . . . . . . . . . . . . . .19 5.3.1 Timestamp Option . . . . . . . . . . . . . . .19
5.3.2 Nonce Option . . . . . . . . . . . . . . . . .20 5.3.2 Nonce Option . . . . . . . . . . . . . . . . .20
5.3.3 Processing rules for senders . . . . . . . . .21 5.3.3 Processing rules for senders . . . . . . . . .21
5.3.4 Processing rules for receivers . . . . . . . .21 5.3.4 Processing rules for receivers . . . . . . . .21
5.4 Proxy Neighbor Discovery . . . . . . . . . . . . . . 23 6. Authorization Delegation Discovery . . . . . . . . . . . . . 24
6. Authorization Delegation Discovery . . . . . . . . . . . . 24 6.1 Certificate Format . . . . . . . . . . . . . . . . . .24
6.1 Certificate Format . . . . . . . . . . . . . . . . . 24
6.1.1 Router Authorization Certificate Profile . . .24 6.1.1 Router Authorization Certificate Profile . . .24
6.2 Certificate Transport . . . . . . . . . . . . . . . 26 6.2 Certificate Transport . . . . . . . . . . . . . . . .26
6.2.1 Delegation Chain Solicitation Message Format .27 6.2.1 Delegation Chain Solicitation Message Format .27
6.2.2 Delegation Chain Advertisement Message Format 29 6.2.2 Delegation Chain Advertisement Message Format 29
6.2.3 Trust Anchor Option . . . . . . . . . . . . .31 6.2.3 Trust Anchor Option . . . . . . . . . . . . .31
6.2.4 Certificate Option . . . . . . . . . . . . . .32 6.2.4 Certificate Option . . . . . . . . . . . . . .32
6.2.5 Processing Rules for Routers . . . . . . . . .33 6.2.5 Processing Rules for Routers . . . . . . . . .33
6.2.6 Processing Rules for Hosts . . . . . . . . . .34 6.2.6 Processing Rules for Hosts . . . . . . . . . .34
7. Securing Neighbor Discovery with SEND . . . . . . . . . . 36 7. Addressing . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1 Neighbor Solicitation Messages . . . . . . . . . . . 36 7.1 CGA Addresses . . . . . . . . . . . . . . . . . . . .36
7.1.1 Sending Secure Neighbor Solicitations . . . .36 7.2 Redirect Addresses . . . . . . . . . . . . . . . . . .36
7.1.2 Receiving Secure Neighbor Solicitations . . .36 7.3 Advertised Prefixes . . . . . . . . . . . . . . . . .36
7.2 Neighbor Advertisement Messages . . . . . . . . . . 36 7.4 Limitations . . . . . . . . . . . . . . . . . . . . .36
7.2.1 Sending Secure Neighbor Advertisements . . . .36 8. Transition Issues . . . . . . . . . . . . . . . . . . . . . 38
7.2.2 Receiving Secure Neighbor Advertisements . . .37 9. Security Considerations . . . . . . . . . . . . . . . . . . 40
7.3 Other Requirements . . . . . . . . . . . . . . . . . 37 9.1 Threats to the Local Link Not Covered by SEND . . . .40
8. Securing Router Discovery with SEND . . . . . . . . . . . 39 9.2 How SEND Counters Threats to NDP . . . . . . . . . . .40
8.1 Router Solicitation Messages . . . . . . . . . . . . 39 9.2.1 Neighbor Solicitation/Advertisement Spoofing . 41
8.1.1 Sending Secure Router Solicitations . . . . .39 9.2.2 Neighbor Unreachability Detection Failure . . 41
8.1.2 Receiving Secure Router Solicitations . . . .39 9.2.3 Duplicate Address Detection DoS Attack . . . . 41
8.2 Router Advertisement Messages . . . . . . . . . . . 39 9.2.4 Router Solicitation and Advertisement Attacks 42
8.2.1 Sending Secure Router Advertisements . . . . .40 9.2.5 Replay Attacks . . . . . . . . . . . . . . . . 42
8.2.2 Receiving Secure Router Advertisements . . . .40 9.2.6 Neighbor Discovery DoS Attack . . . . . . . . 43
8.3 Redirect Messages . . . . . . . . . . . . . . . . . 40 9.3 Attacks against SEND Itself . . . . . . . . . . . . .43
8.3.1 Sending Redirects . . . . . . . . . . . . . .41 10. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 45
8.3.2 Receiving Redirects . . . . . . . . . . . . .41 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 46
8.4 Other Requirements . . . . . . . . . . . . . . . . . 41 Normative References . . . . . . . . . . . . . . . . . . . . 47
9. Co-Existence of SEND and non-SEND nodes . . . . . . . . . 43 Informative References . . . . . . . . . . . . . . . . . . . 48
10. Performance Considerations . . . . . . . . . . . . . . . . 45 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 49
11. Security Considerations . . . . . . . . . . . . . . . . . 46 A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 50
11.1 Threats to the Local Link Not Covered by SEND . . . 46 B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 51
11.2 How SEND Counters Threats to Neighbor Discovery . . 46 C. Cache Management . . . . . . . . . . . . . . . . . . . . . . 52
11.2.1 Neighbor Solicitation/Advertisement Spoofing .47 Intellectual Property and Copyright Statements . . . . . . . 53
11.2.2 Neighbor Unreachability Detection Failure . .47
11.2.3 Duplicate Address Detection DoS Attack . . . .47
11.2.4 Router Solicitation and Advertisement Attacks 48
11.2.5 Replay Attacks . . . . . . . . . . . . . . . .48
11.2.6 Neighbor Discovery DoS Attack . . . . . . . .49
11.3 Attacks against SEND Itself . . . . . . . . . . . . 49
12. Protocol Constants . . . . . . . . . . . . . . . . . . . . 51
13. IANA Considerations . . . . . . . . . . . . . . . . . . . 52
Normative References . . . . . . . . . . . . . . . . . . . 53
Informative References . . . . . . . . . . . . . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 55
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . 57
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 58
C. Cache Management . . . . . . . . . . . . . . . . . . . . . 59
D. Comparison to AH-Based Approach . . . . . . . . . . . . . 60
Intellectual Property and Copyright Statements . . . . . . 63
1. Introduction 1. Introduction
IPv6 defines the Neighbor Discovery Protocol (NDP) in RFC 2461 [7]. IPv6 defines the Neighbor Discovery Protocol (NDP) in RFCs 2461 [7]
Nodes on the same link use NDP to discover each other's presence, to and 2462 [8]. Nodes on the same link use NDP to discover each
determine each other's link-layer addresses, to find routers, and to other's presence, to determine each other's link-layer addresses, to
maintain reachability information about the paths to active find routers, and to maintain reachability information about the
neighbors. NDP is used both by hosts and routers. Its functions paths to active neighbors. NDP is used both by hosts and routers.
include Neighbor Discovery (ND), Router Discovery (RD), Address Its functions include Neighbor Discovery (ND), Router Discovery (RD),
Autoconfiguration, Address Resolution, Neighbor Unreachability Address Autoconfiguration, Address Resolution, Neighbor
Detection (NUD), Duplicate Address Detection (DAD), and Redirection. Unreachability Detection (NUD), Duplicate Address Detection (DAD),
and Redirection.
RFC 2461 called for the use of IPsec for protecting the NDP messages. Original NDP specifications called for the use of IPsec for
However, it does not specify detailed instructions for using IPsec to protecting the NDP messages. However, the RFCs do not give detailed
secure NDP. It turns out that in this particular application, IPsec instructions for using IPsec to secure NDP. It turns out that in
can only be used with a manual configuration of security this particular application, IPsec can only be used with a manual
associations, due to chicken-and-egg problems in using IKE [22, 17]. configuration of security associations, due to chicken-and-egg
Furthermore, the number of such manually configured security problems in using IKE [20, 15]. Furthermore, the number of such
associations needed for protecting NDP can be very large [23], making manually configured security associations needed for protecting NDP
that approach impractical for most purposes. can be very large [21], making that approach impractical for most
purposes.
This document is organized as follows. Section 4 describes the This document is organized as follows. Section 4 describes the
overall approach to securing NDP. This approach involves the use of overall approach to securing NDP. This approach involves the use of
new NDP options to carry public-key based signatures. A new NDP options to carry public-key based signatures. A
zero-configuration mechanism is used for showing address ownership on zero-configuration mechanism is used for showing address ownership on
individual nodes; routers are certified by a trust anchor [10]. The individual nodes; routers are certified by a trust anchor [10]. The
formats, procedures, and cryptographic mechanisms for the formats, procedures, and cryptographic mechanisms for the
zero-configuration mechanism are described in a related specification zero-configuration mechanism are described in a related specification
[12]. [12].
Section 6 describes the mechanism for distributing certificate chains The required new NDP options are discussed in Section 5. Section 6
to establish an authorization delegation chain to a common trust describes the mechanism for distributing certificate chains to
anchor. The required new NDP options are discussed in Section 5. establish an authorization delegation chain to a common trust anchor.
Section 7 and Section 8 show how to apply these components to
securing Neighbor and Router Discovery.
Finally, Section 9 discusses the co-existence of secure and Finally, Section 8 discusses the co-existence of secure and
non-secure Neighbor Discovery on the same link, Section 10 discusses non-secure NDP on the same link and Section 9 discusses security
performance considerations, and Section 11 discusses security
considerations for Secure Neighbor Discovery. considerations for Secure Neighbor Discovery.
1.1 Specification of Requirements 1.1 Specification of Requirements
In this document, several words are used to signify the requirements In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. The key of the specification. These words are often capitalized. The key
words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", and
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document "MAY" in this document are to be interpreted as described in [2].
are to be interpreted as described in [2].
2. Terms 2. Terms
Authorization Delegation Discovery (ADD) Authorization Delegation Discovery (ADD)
A process through which SEND nodes can acquire a certificate chain A process through which SEND nodes can acquire a certificate chain
from a peer node to a trust anchor. from a peer node to a trust anchor.
Cryptographically Generated Addresses (CGAs) Cryptographically Generated Address (CGA)
A technique [12] where the IPv6 address of a node is A technique [12] where the IPv6 address of a node is
cryptographically generated using a one-way hash function from the cryptographically generated using a one-way hash function from the
node's public key and some other parameters. node's public key and some other parameters.
Duplicate Address Detection (DAD) Duplicate Address Detection (DAD)
A mechanism defined in RFC 2462 [8] that assures that two IPv6 A mechanism that assures that two IPv6 nodes on the same link are
nodes on the same link are not using the same addresses. not using the same addresses.
Internet Control Message Protocol version 6 (ICMPv6) Internet Control Message Protocol version 6 (ICMPv6)
The IPv6 control signaling protocol. Neighbor Discovery is a part The IPv6 control signaling protocol. Neighbor Discovery Protocol
of ICMPv6. is a part of ICMPv6.
Neighbor Discovery Protocol (NDP) Neighbor Discovery Protocol (NDP)
The IPv6 Neighbor Discovery Protocol [7]. The IPv6 Neighbor Discovery Protocol [7, 8].
Neighbor Discovery (ND) Neighbor Discovery (ND)
The Neighbor Discovery function of the Neighbor Discovery Protocol The Neighbor Discovery function of the Neighbor Discovery Protocol
(NDP). NDP contains also other functions but ND. (NDP). NDP contains also other functions but ND.
Neighbor Unreachability Detection (NUD) Neighbor Unreachability Detection (NUD)
This mechanism defined in RFC 2461 [7] is used for tracking the This mechanism is used for tracking the reachability of neighbors.
reachability of neighbors.
Nonce Nonce
A random number generated by a node and used exactly once, and A random number generated by a node and used exactly once. In
never again. In SEND, nonces are used to ensure that a particular SEND, nonces are used to ensure that a particular advertisement is
advertisement is linked to the solicitation that triggered it. linked to the solicitation that triggered it.
Router Authorization Certificate Router Authorization Certificate
An X.509v3 [10] PKC certificate using the profile specified in An X.509v3 [10] PKC certificate using the profile specified in
Section 6.1.1. Section 6.1.1.
SEND node SEND node
An IPv6 node that implements this specification. An IPv6 node that implements this specification.
non-SEND node non-SEND node
An IPv6 node that does not implement this specification but uses An IPv6 node that does not implement this specification but uses
the legacy RFC 2461 and RFC 2462 mechanisms. the legacy RFC 2461 and RFC 2462 mechanisms.
Router Discovery (RD) Router Discovery (RD)
The Router Discovery function of the Neighbor Discovery Protocol The Router Discovery function of the Neighbor Discovery Protocol.
(NDP).
3. Neighbor and Router Discovery Overview 3. Neighbor and Router Discovery Overview
IPv6 Neighbor and Router Discovery have several functions. Many of The Neighbor Discovery Protocol has several functions. Many of these
these functions are overloaded on a few central message types, such functions are overloaded on a few central message types, such as the
as the ICMPv6 Neighbor Discovery message. In this section we review ICMPv6 Neighbor Advertisement message. In this section we review
some of these tasks and their effects in order to understand better some of these tasks and their effects in order to understand better
how the messages should be treated. This section is not normative, how the messages should be treated. This section is not normative,
and if this section and the original Neighbor Discovery RFCs are in and if this section and the original Neighbor Discovery RFCs are in
conflict, the original RFCs take precedence. conflict, the original RFCs take precedence.
In IPv6, many of the tasks traditionally performed at lower the The main functions of NDP are the following.
layers, such as ARP, have been moved to the IP layer. As a
consequence, a set of unified mechanisms can be applied across link
layers, any introduced security mechanisms or other extensions can be
adopted more easily, and a clear separation of the roles between the
IP and link layer has been achieved.
The main functions of IPv6 Neighbor Discovery are the following.
o The Router Discovery function allows IPv6 hosts to discover the o The Router Discovery function allows IPv6 hosts to discover the
local routers on an attached link. Router Discovery is described local routers on an attached link. Router Discovery is described
in Section 6 of RFC 2461 [7]. The main purpose of Router in Section 6 of RFC 2461 [7]. The main purpose of Router
Discovery is to find neighboring routers that are willing to Discovery is to find neighboring routers that are willing to
forward packets on behalf of hosts. Prefix discovery involves forward packets on behalf of hosts. Prefix discovery involves
determining which destinations are directly on a link; this determining which destinations are directly on a link; this
information is necessary in order to know whether a packet should information is necessary in order to know whether a packet should
be sent to a router or to the destination node directly. be sent to a router or to the destination node directly.
o The Redirect function is used for automatically redirecting a host o The Redirect function is used for automatically redirecting a host
to a better first-hop router, or to inform hosts that a to a better first-hop router, or to inform hosts that a
destination is in fact a neighbor (i.e., on-link). Redirect is destination is in fact a neighbor (i.e., on-link). Redirect is
specified in Section 8 of RFC 2461 [7]. It is similar to the specified in Section 8 of RFC 2461 [7].
ICMPv4 Redirect function [15].
o Address Autoconfiguration is used for automatically assigning o Address Autoconfiguration is used for automatically assigning
addresses to a host [8]. This allows hosts to operate without addresses to a host [8]. This allows hosts to operate without
explicit configuration related to IP connectivity. The Address explicit configuration related to IP connectivity. The default
Autoconfiguration mechanism defined in [8] is stateless. To autoconfiguration mechanism is stateless. To create IP addresses,
create IP addresses, the hosts use any prefix information the hosts use any prefix information delivered to them during
delivered to them during Router Discovery, and then test the newly Router Discovery, and then test the newly formed addresses for
formed addresses for uniqueness. A stateful mechanism, DHCPv6 uniqueness. A stateful mechanism, DHCPv6 [23], provides
[25], provides additional Autoconfiguration features. additional autoconfiguration features.
o Duplicate Address Detection (DAD) is used for preventing address o Duplicate Address Detection (DAD) is used for preventing address
collisions [8], for instance during Address Autoconfiguration. A collisions [8], for instance during Address Autoconfiguration. A
node that intends to assign a new address to one of its interfaces node that intends to assign a new address to one of its interfaces
first runs the DAD procedure to verify that there is no other node first runs the DAD procedure to verify that there is no other node
using the same address. Since the rules forbid the use of an using the same address. Since the rules forbid the use of an
address until it has been found unique, no higher layer traffic is address until it has been found unique, no higher layer traffic is
possible until this procedure has been completed. Thus, possible until this procedure has been completed. Thus,
preventing attacks against DAD can help ensure the availability of preventing attacks against DAD can help ensure the availability of
communications for the node in question. communications for the node in question.
o Address Resolution is similar to IPv4 ARP [16]. The Address o The Address Resolution function resolves a node's IPv6 address to
Resolution function resolves a node's IPv6 address to the the corresponding link-layer address for nodes on the link.
corresponding link-layer address for nodes on the link. Address Address Resolution is defined in Section 7.2 of RFC 2461 [7], and
Resolution is defined in Section 7.2 of RFC 2461 [7], and it is it is used for hosts and routers alike. Again, no higher level
used for hosts and routers alike. Again, no higher level traffic traffic can proceed until the sender knows the hardware address of
can proceed until the sender knows the hardware address of the the destination node or the next hop router. Note the source link
destination node or the next hop router. Note that like its layer address is not checked against the information learned
predecessor in ARP, IPv6 Neighbor Discovery does not check the through Address Resolution. This allows for an easier addition of
source link layer address against the information learned through network elements such as bridges and proxies, and eases the stack
Address Resolution. This allows for an easier addition of network
elements such as bridges and proxies, and eases the stack
implementation requirements as less information needs to be passed implementation requirements as less information needs to be passed
from layer to layer. from layer to layer.
o Neighbor Unreachability Detection (NUD) is used for tracking the o Neighbor Unreachability Detection (NUD) is used for tracking the
reachability of neighboring nodes, both hosts and routers. NUD is reachability of neighboring nodes, both hosts and routers. NUD is
defined in Section 7.3 of RFC 2461 [7]. NUD is defined in Section 7.3 of RFC 2461 [7]. NUD is
security-sensitive, because an attacker could falsely claim that security-sensitive, because an attacker could falsely claim that
reachability exists when it in fact does not. reachability exists when it in fact does not.
The Neighbor Discovery messages follow the ICMPv6 message format. The NDP messages follow the ICMPv6 message format. All NDP functions
The actual Neighbor Discovery message includes an NDP message header, are realized using the Router Solicitation (RS), Router Advertisement
consisting of an ICMPv6 header and ND message-specific data, and zero (RA), Neighbor Solicitation (NS), Neighbor Advertisement (NA), and
or more NDP options. Redirect messages. An actual NDP message includes an NDP message
header, consisting of an ICMPv6 header and ND message-specific data,
and zero or more NDP options. The NDP message options are formatted
in the Type-Length-Value format.
<------------NDP Message----------------> <------------NDP Message---------------->
*-------------------------------------------------------------* *-------------------------------------------------------------*
| IPv6 Header | ICMPv6 | ND message- | ND Message | | IPv6 Header | ICMPv6 | ND message- | ND Message |
| Next Header = 58 | Header | specific | Options | | Next Header = 58 | Header | specific | Options |
| (ICMPv6) | | data | | | (ICMPv6) | | data | |
*-------------------------------------------------------------* *-------------------------------------------------------------*
<--NDP Message header--> <--NDP Message header-->
The NDP message options are formatted in the Type-Length-Value
format.
All IPv6 NDP functions are realized using the following ICMPv6
messages:
ICMPv6 Type Message
------------------------------------
133 Router Solicitation (RS)
134 Router Advertisement (RA)
135 Neighbor Solicitation (NS)
136 Neighbor Advertisement (NA)
137 Redirect
The various functions are realized using these messages as follows:
o Router Discovery uses the RS and RA messages.
o Duplicate Address Detection uses the NS and NA messages.
o Address Autoconfiguration uses the NS, NA, RS, and RA messages.
o Address Resolution uses the NS and NA messages.
o Neighbor Unreachability Detection uses the NS and NA messages.
o Redirect uses the Redirect message.
4. Secure Neighbor Discovery Overview 4. Secure Neighbor Discovery Overview
To secure the various functions, a set of new Neighbor Discovery To secure the various functions, a set of new Neighbor Discovery
options is introduced. They are used in to protect Neighbor and options is introduced. They are used in to protect NDP messages.
Router Discovery messages. This specification introduces these This specification introduces these options, an authorization
options, an authorization delegation discovery process, an address delegation discovery process, an address ownership proof mechanism,
ownership proof mechanism, and requirements for the use of these and requirements for the use of these components in NDP.
components for Neighbor Discovery.
The components of the solution specified in this document are as The components of the solution specified in this document are as
follows: follows:
o Certificate chains, anchored on trusted parties, are expected to o Certificate chains, anchored on trusted parties, are expected to
certify the authority of routers. A host and a router must have certify the authority of routers. A host and a router must have
at least one common trust anchor before the host can adopt the at least one common trust anchor before the host can adopt the
router as its default router. Delegation Chain Solicitation and router as its default router. Delegation Chain Solicitation and
Advertisement messages are used to discover a certificate chain to Advertisement messages are used to discover a certificate chain to
the trust anchor without requiring the actual Router Discovery the trust anchor without requiring the actual Router Discovery
messages to carry lengthy certificate chains. messages to carry lengthy certificate chains. The receipt of a
protected Router Advertisement message for which no certificate
chain is available triggers this process.
o Cryptographically Generated Addresses are used to assure that the o Cryptographically Generated Addresses are used to assure that the
sender of a Neighbor or Router Advertisement is the "owner" of the sender of a Neighbor or Router Advertisement is the "owner" of the
claimed address. A public-private key pair needs to be generated claimed address. A public-private key pair needs to be generated
by all nodes before they can claim an address. A new Neighbor by all nodes before they can claim an address. A new NDP option,
Discovery option, the CGA option, is used to carry the public key the CGA option, is used to carry the public key and associated
and associated parameters. parameters.
This specification also allows one to use non-CGA addresses and to This specification also allows one to use non-CGA addresses and to
use certificates to authorized their use. However, the details of use certificates to authorize their use. However, the details of
such use have been left for future work. such use have been left for future work.
o A new Neighbor Discovery option, the Signature option, is used to o A new NDP option, the Signature option, is used to protect all
protect all messages relating to Neighbor and Router discovery. messages relating to Neighbor and Router discovery.
Public key signatures are used to protect the integrity of the Public key signatures are used to protect the integrity of the
messages and to authenticate the identity of their sender. The messages and to authenticate the identity of their sender. The
authority of a public key is established either with the authority of a public key is established either with the
authorization delegation process, using certificates, or through authorization delegation process, using certificates, or through
the address ownership proof mechanism, using CGAs, or both, the address ownership proof mechanism, using CGAs, or both,
depending on configuration and the type of the message protected. depending on configuration and the type of the message protected.
o In order to prevent replay attacks, two new Neighbor Discovery o In order to prevent replay attacks, two new Neighbor Discovery
options, Timestamp and Nonce, are used. Given that Neighbor and options, Timestamp and Nonce, are used. Given that Neighbor and
Router Discovery messages are in some cases sent to multicast Router Discovery messages are in some cases sent to multicast
addresses, the Timestamp option offers replay protection without addresses, the Timestamp option offers replay protection without
any previously established state or sequence numbers. When the any previously established state or sequence numbers. When the
messages are used in solicitation - advertisement pairs, they messages are used in solicitation - advertisement pairs, they are
protected using the Nonce option. protected using the Nonce option.
5. Neighbor Discovery Options 5. Neighbor Discovery Protocol Options
The following new NDP options and mechanisms are REQUIRED to be
implemented by all SEND nodes:
o The CGA option MAY be present in all Neighbor Discovery messages,
and SHOULD be present in most cases.
o The Signature option is REQUIRED in all Neighbor Discovery
messages.
o The Nonce option is REQUIRED in all Neighbor Discovery
solicitations, and in all solicited advertisements.
o The Timestamp option is REQUIRED in all Neighbor Discovery
advertisements and Redirects.
o Proxy Neighbor Discovery is not supported by this specification; The options described in this section MUST be supported by all SEND
it is planned to be specified in a future document. nodes.
5.1 CGA Option 5.1 CGA Option
The CGA option allows the verification of the sender's CGA. The The CGA option allows the verification of the sender's CGA. The
format of the CGA option is described as follows. format of the CGA option is described as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Collision Cnt | Reserved | | Type | Length | Collision Cnt | Reserved |
  Skipping to change at page 13, line 8:
Padding Padding
A variable length field making the option length a multiple of 8. A variable length field making the option length a multiple of 8.
It begins after the ASN.1 encoding of the previous field has ends, It begins after the ASN.1 encoding of the previous field has ends,
and continues to the end of the option, as specified by the Length and continues to the end of the option, as specified by the Length
field. field.
5.1.1 Processing Rules for Senders 5.1.1 Processing Rules for Senders
The CGA option MUST be present in all Neighbor Solicitation and
Advertisement messages, and in Router Solicitation messages not sent
with the unspecified source address. The CGA option MAY be present
in other messages.
A node sending a message using the CGA option MUST construct the A node sending a message using the CGA option MUST construct the
message as follows. message as follows.
The Modifier, Collision Cnt, and Key Information fields in the CGA The Modifier, Collision Cnt, and Key Information fields in the CGA
option are filled in according to the rules presented above and in option are filled in according to the rules presented above and in
[12]. The used public key is taken from configuration; typically [12]. The used public key is taken from configuration; typically
from a data structure associated with the source address. from a data structure associated with the source address. The
address MUST be constructed as specified in Section 4 of [12].
An address MUST be constructed as specified in Section 4 of [12]. In
the typical case, the address is constructed long before it is used.
Depending on the type of the message, this address appears in Depending on the type of the message, this address appears in
different places: different places:
Redirect Redirect
The address MUST be the source address of the message. The address MUST be the source address of the message.
Neighbor Solicitation Neighbor Solicitation
The address MUST be the Target Address for solicitations sent for The address MUST be the Target Address for solicitations sent for
the purpose of Duplicate Address Detection, and the source address the purpose of Duplicate Address Detection, and the source address
of the message otherwise. of the message otherwise.
Neighbor Advertisement Neighbor Advertisement
The address MUST be the source address of the message. The address MUST be the source address of the message.
Router Solicitation Router Solicitation
The address MUST be the source address of the message, unless the The address MUST be the source address of the message. Note that
source address is the unspecified address. the CGA option is not used when the source address is the
unspecified address.
Router Advertisement Router Advertisement
The address MUST be the source address of the message. The address MUST be the source address of the message.
5.1.2 Processing Rules for Receivers 5.1.2 Processing Rules for Receivers
Neighbor Solicitation and Advertisement messages without the CGA
option MUST be silently discarded. Router Solicitation messages
without the CGA option MUST be silently discarded, unless the source
address of the message is the unspecified address.
A message containing a CGA option MUST be checked as follows: A message containing a CGA option MUST be checked as follows:
If the interface has been configued to use CGA, it is REQUIRED If the interface has been configured to use CGA, the receiving
that the receiving node verifies the source address of the packet node MUST verify the source address of the packet using the
using the algorithm described in Section 5 of [12]. The inputs algorithm described in Section 5 of [12]. The inputs for the
for the algorithm are the contents of the Collision Cnt, Modifier, algorithm are the contents of the Collision Cnt, Modifier, and the
and the Key Information fields, the claimed address in the packet Key Information fields, the claimed address in the packet (as
(as discussed in the previous section), and the minimum acceptable discussed in the previous section), and the minimum acceptable Sec
Sec value. If the CGA verification is successful, the recipient value. If the CGA verification is successful, the recipient
proceeds with the cryptographically more time consuming check of proceeds with the cryptographically more time consuming check of
the signature. the signature.
Note that a receiver which does not support CGA or has not specified Note that a receiver which does not support CGA or has not specified
its use for a given interface can still verify packets using trust its use for a given interface can still verify packets using trust
anchors, even if CGA had been used on a packet. In such a case, the anchors, even if CGA had been used on a packet. In such a case, the
CGA property of the address is simply left unverified. CGA property of the address is simply left unverified.
5.1.3 Configuration 5.1.3 Configuration
All nodes that support the verification of the CGA option MUST record All nodes that support the verification of the CGA option MUST record
the following configuration information: the following configuration information:
minbits minbits
The minimum acceptable key length for the public keys used in the The minimum acceptable key length for the public keys used in the
generation of the CGA address. The default SHOULD be 1024 bits. generation of the CGA address. The default SHOULD be 1024 bits.
Implementations MAY also set an upper limit in order to limit the Implementations MAY also set an upper limit in order to limit the
amount of computation they need to perform when verifying packets amount of computation they need to perform when verifying packets
that use these security associations. Any implementation should that use these security associations. Any implementation should
follow prudent cryptographic practise in determining the follow prudent cryptographic practice in determining the
appropriate key lengths. appropriate key lengths.
minSec
The minimum acceptable Sec value, if CGA verification is required
(see Section 2 in [12]). This parameter is intended to facilitate
future extensions and experimental work. Currently, the minSec
value SHOULD always be set to zero.
All nodes that support the sending of the CGA option MUST record the
following configuration information:
CGA parameters
Any information required to construct CGAs, including the used Sec
and Modifier values, and the CGA address itself.
5.2 Signature Option 5.2 Signature Option
The Signature option allows public-key based signatures to be The Signature option allows public-key based signatures to be
attached to NDP messages. Both trust anchor authentication and CGAs attached to NDP messages. Both trust anchor authentication and CGAs
can be used. The format of the Signature option is described in the can be used. The format of the Signature option is described in the
following: following:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  Skipping to change at page 16, line 16:
associate the signature to a particular key known by the receiver. associate the signature to a particular key known by the receiver.
Such a key can be either stored in the certificate cache of the Such a key can be either stored in the certificate cache of the
receiver, or be received in the CGA option in the same message. receiver, or be received in the CGA option in the same message.
Digital Signature Digital Signature
A variable length field contains the signature constructed using A variable length field contains the signature constructed using
the sender's private key, over the the following sequence of the sender's private key, over the the following sequence of
octets: octets:
1. The 128-bit CGA Type Tag [12] value for SEND, 0xXXXX XXXX XXXX 1. The 128-bit CGA Type Tag [12] value for SEND, 0x086F CA5E 10B2
XXXX XXXX XXXX XXXX XXXX (To be generated randomly). 00C9 9C8C E001 6427 7C08 (generated randomly).
2. The 128-bit Source Address field from the IP header. 2. The 128-bit Source Address field from the IP header.
3. The 128-bit Destination Address field from the IP header. 3. The 128-bit Destination Address field from the IP header.
4. The 32-bit ICMP header, i.e., the Type, Code, and Checksum 4. The 32-bit ICMP header.
fields.
5. The Neighbor Discovery message header, i.e., the Reserved 5. The NDP message header.
field in the Router Solicitation message, the Cur Hop Limit,
M, O, Reserved, Router Lifetime, Reachable Time, and Retrans
Timer fields in the Router Advertisement message, Reserved and
Target Address fields in the Neighbor Solicitation message, R,
S, O, Reserved, and Target Address fields in the Neighbor
Advertisement message, and Reserved, Target Address, and
Destination Address fields in the Redirect message.
6. All NDP options preceding the Signature option. 6. All NDP options preceding the Signature option.
The signature is constructed using the RSA algorithm and MUST be The signature is constructed using the RSA algorithm and MUST be
encoded as private key encryption in PKCS#1 format [13]. The encoded as private key encryption in PKCS#1 format [13]. The
signature value is computed with the RSASSA-PKCS1-v1_5 algorithm signature value is computed with the RSASSA-PKCS1-v1_5 algorithm
and SHA-1 hash as defined in [13]. and SHA-1 hash as defined in [13].
This field starts after the Key Hash field. The length of the This field starts after the Key Hash field. The length of the
Digital Signature field is determined by the length of the Digital Signature field is determined by the length of the
Signature option minus the length of the other fields (including Signature option minus the length of the other fields (including
the variable length Pad field). the variable length Pad field).
This variable length field contains padding, as many bytes as is This variable length field contains padding, as many bytes as is
given by the Pad Length Field. given by the Pad Length Field.
5.2.1 Processing Rules for Senders 5.2.1 Processing Rules for Senders
Neighbor Solicitation, Neighbor Advertisement, Router Advertisement,
and Redirect messages MUST contain the Signature option. Router
Solicitation messages not sent with the unspecified source address
MUST contain the Signature option.
A node sending a message using the Signature option MUST construct A node sending a message using the Signature option MUST construct
the message as follows: the message as follows:
o The message is constructed in its entirety. o The message is constructed in its entirety, without the Signature
option.
o The Signature option is added as the last option in the message. o The Signature option is added as the last option in the message.
o For the purpose of constructing a signature, the following data o For the purpose of constructing a signature, the following data
items are concatenated: items are concatenated:
* The 128-bit CGA Type Tag. * The 128-bit CGA Type Tag.
* The source address of the message. * The source address of the message.
  Skipping to change at page 17, line 32:
* The contents of the message, starting from the ICMPv6 header, * The contents of the message, starting from the ICMPv6 header,
up to but excluding the Signature option. up to but excluding the Signature option.
o The message, in the form defined above, is signed using the o The message, in the form defined above, is signed using the
configured private key, and the resulting PKCS#1 signature is put configured private key, and the resulting PKCS#1 signature is put
to the Digital Signature field. to the Digital Signature field.
5.2.2 Processing Rules for Receivers 5.2.2 Processing Rules for Receivers
Neighbor Solicitation, Neighbor Advertisement, Router Advertisement,
and Redirect messages without the Signature option MUST be silently
discarded. Router Solicitation messages without the Signature option
MUST be silently discarded, unless the source address of the message
is the unspecified address.
A message containing a Signature option MUST be checked as follows: A message containing a Signature option MUST be checked as follows:
o The Signature option MUST appear as the last option. o The Signature option MUST appear as the last option.
o The Key Hash field MUST indicate the use of a known public key, o The Key Hash field MUST indicate the use of a known public key,
either one learned from a preceding CGA option, or one known by either one learned from a preceding CGA option, or one known by
other means. other means.
o The Digital Signature field MUST have correct encoding, and do not o The Digital Signature field MUST have correct encoding, and not
exceed the length of the Signature option. exceed the length of the Signature option.
o The Digital Signature verification MUST show that the signature o The Digital Signature verification MUST show that the signature
has been calculated as specified in the previous section. has been calculated as specified in the previous section.
o If the use of a trust anchor has been configured, a valid o If the use of a trust anchor has been configured, a valid
authorization delegation chain MUST be known between the authorization delegation chain MUST be known between the
receiver's trust anchor and the sender's public key. receiver's trust anchor and the sender's public key.
Note that the receiver may verify just the CGA property of a Note that the receiver may verify just the CGA property of a
packet, even if, in addition to CGA, the sender has used a trust packet, even if, in addition to CGA, the sender has used a trust
anchor. anchor.
Messages that do not pass all the above tests MUST be silently Messages that do not pass all the above tests MUST be silently
discarded. The receiver MAY silently drop packets also otherwise, discarded. The receiver MAY silently discard packets also otherwise,
e.g., as a response to an apparent CPU exhausting DoS attack. e.g., as a response to an apparent CPU exhausting DoS attack.
5.2.3 Configuration 5.2.3 Configuration
All nodes that support the reception of the Signature options MUST All nodes that support the reception of the Signature options MUST
record the following configuration information for each separate record the following configuration information for each separate NDP
Neighbor Discovery Protocol message type: message type:
authorization method authorization method
This parameter determines the method through which the authority This parameter determines the method through which the authority
of the sender is determined. It can have four values: of the sender is determined. It can have four values:
trust anchor trust anchor
The authority of the sender is verified as described in Section The authority of the sender is verified as described in Section
6.1. The sender may claim additional authorization through the 6.1. The sender may claim additional authorization through the
  Skipping to change at page 18, line 44:
trust anchor and CGA trust anchor and CGA
Both the trust anchor and the CGA verification is required. Both the trust anchor and the CGA verification is required.
trust anchor or CGA trust anchor or CGA
Either the trust anchor or the CGA verification is required. Either the trust anchor or the CGA verification is required.
anchor anchor
The public keys of the allowed trust anchor(s), if authorization The public keys and names of the allowed trust anchor(s), if
method is not set to CGA. authorization method is not set to CGA.
minSec
The minimum acceptable Sec value, if CGA verification is required
(see Section 2 in [12]). This parameter is intended to facilitate
future extensions and experimental work. Currently, the minSec
value SHOULD always be set to zero.
All nodes that support the sending of Signature options MUST record All nodes that support the sending of Signature options MUST record
the following configuration information: the following configuration information:
keypair keypair
A public-private key pair. If authorization delegation is in use, A public-private key pair. If authorization delegation is in use,
there must exist a delegation chain from a trust anchor to this there must exist a delegation chain from a trust anchor to this
key pair. key pair.
CGA flag CGA flag
A flag that indicates whether CGA is used or is not used. This A flag that indicates whether CGA is used or is not used. This
flag may be per interface or per node. flag may be per interface or per node.
CGA parameters 5.2.4 Performance Considerations
Optionally any information required to construct CGAs, including The construction and verification of this option is computationally
the used Sec and Modifier values, and the CGA address itself. expensive. In the NDP context, however, the hosts typically have the
need to perform only a few signature operations as they enter a link,
and a few operations as they find a new on-link peer with which to
communicate.
Routers are required to perform a larger number of operations,
particularly when the frequency of router advertisements is high due
to mobility requirements. Still, the number of required signature
operations is on the order of a few dozen ones per second, some of
which can be precomputed as discussed below. A large number of
router solicitations may cause higher demand for performing
asymmetric operations, although RFC 2461 limits the rate at which
responses to solicitations can be sent.
Signatures can be precomputed for unsolicited (multicast) Neighbor
and Router Advertisements, if the timing of such future
advertisements is known. Typically, solicited advertisements are
sent to the unicast address from which the solicitation was sent.
Given that the IPv6 header is covered by the signature, it is not
possible to precompute solicited-for advertisements.
5.3 Timestamp and Nonce options 5.3 Timestamp and Nonce options
5.3.1 Timestamp Option 5.3.1 Timestamp Option
The purpose of the Timestamp option is to ensure that unsolicited The purpose of the Timestamp option is to ensure that unsolicited
advertisements and redirects have not been replayed. The format of advertisements and redirects have not been replayed. The format of
the Timestamp option is described in the following: this option is described in the following:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved | | Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Timestamp + + Timestamp +
  Skipping to change at page 20, line 28:
indicates the number of seconds since January 1,, 1970 00:00 UTC, indicates the number of seconds since January 1,, 1970 00:00 UTC,
using a fixed point format. In this format the integer number of using a fixed point format. In this format the integer number of
seconds is contained in the first 48 bits of the field, and the seconds is contained in the first 48 bits of the field, and the
remaining 16 bits indicate the number of 1/64K fractions of a remaining 16 bits indicate the number of 1/64K fractions of a
second. second.
5.3.2 Nonce Option 5.3.2 Nonce Option
The purpose of the Nonce option is to ensure that an advertisement is The purpose of the Nonce option is to ensure that an advertisement is
a fresh response to a solicitation sent earlier by the receiving same a fresh response to a solicitation sent earlier by the receiving same
node. The format of the Nonce option is as described in the node. The format of this option is described in the following:
following:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Nonce ... | | Type | Length | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
. . . .
. . . .
| | | |
  Skipping to change at page 21, line 14:
Nonce Nonce
A field containing a random number selected by the sender of the A field containing a random number selected by the sender of the
solicitation message. The length of the random number MUST be at solicitation message. The length of the random number MUST be at
least 6 bytes. least 6 bytes.
5.3.3 Processing rules for senders 5.3.3 Processing rules for senders
All solicitation messages MUST include a Nonce. All solicited-for All solicitation messages MUST include a Nonce. All solicited-for
announcements MUST include a Nonce, copying the nonce value from the advertisements MUST include a Nonce, copying the nonce value from the
received solicitation. When sending a solication, the sender MUST received solicitation. When sending a solicitation, the sender MUST
store the nonce internally so that it can recognize any replies store the nonce internally so that it can recognize any replies
containing that particular nonce. containing that particular nonce.
All NDP messages MUST include a Timestamp. Senders SHOULD set the All solicitation, advertisement, and redirect messages MUST include a
Timestamp field to the current time, according to their real time Timestamp. Senders SHOULD set the Timestamp field to the current
clock. time, according to their real time clock.
If a message has both Nonce and Timestamp options, the Nonce option If a message has both Nonce and Timestamp options, the Nonce option
SHOULD precede the Timestamp option in order. The receiver MUST be SHOULD precede the Timestamp option in order.
prepared to receive them in any order, as per RFC 2461 [7] Section 9.
5.3.4 Processing rules for receivers 5.3.4 Processing rules for receivers
The processing of the Nonce and Timestamp options depends on whether The processing of the Nonce and Timestamp options depends on whether
a packet is a solicited-for advertisement or not. A system may a packet is a solicited-for advertisement or not. A system may
implement the distinction in various means. Section 5.3.4.1 defines implement the distinction in various means. Section 5.3.4.1 defines
the processing rules for solicited-for advertisements. Section the processing rules for solicited-for advertisements. Section
5.3.4.2 defines the processing rules for all other messages. 5.3.4.2 defines the processing rules for all other messages.
An implementation may utilize some mechanism such as a timestamp In addition, the following rules apply in any case:
o Messages received without the Timestamp option MUST be silently
discarded.
o Solicitation messages received without the Nonce option MUST be
silently discarded.
o Advertisements sent to a unicast destination address without a
Nonce option MUST be silently discarded.
o An implementation may utilize some mechanism such as a timestamp
cache to strengthen resistance to replay attacks. When there is a cache to strengthen resistance to replay attacks. When there is a
very large number of nodes on the same link, or when a cache filling very large number of nodes on the same link, or when a cache
attack is in progress, it is possible that the cache holding the most filling attack is in progress, it is possible that the cache
recent timestamp per sender becomes full. In this case the node MUST holding the most recent timestamp per sender becomes full. In
remove some entries from the cache or refuse some new requested this case the node MUST remove some entries from the cache or
entries. The specific policy as to which entries are preferred over refuse some new requested entries. The specific policy as to
the others is left as an implementation decision. However, typical which entries are preferred over the others is left as an
policies may prefer existing entries over new ones, CGAs with a large implementation decision. However, typical policies may prefer
Sec value over smaller Sec values, and so on. The issue is briefly existing entries over new ones, CGAs with a large Sec value over
discussed in Appendix C. smaller Sec values, and so on. The issue is briefly discussed in
Appendix C.
o The receiver MUST be prepared to receive the Timestamp and Nonce
options in any order, as per RFC 2461 [7] Section 9.
5.3.4.1 Processing solicited-for advertisements 5.3.4.1 Processing solicited-for advertisements
The receiver MUST verify that it has recently send a matching The receiver MUST verify that it has recently sent a matching
solicitation, and that the received advertisement does contain a copy solicitation, and that the received advertisement contains a copy of
of the Nonce sent in the solicitation. the Nonce sent in the solicitation.
If the message does not contain a Nonce option, it MAY be considered If the message contains a Nonce option, but the Nonce value is not
as a non-solicited-for announcement, and processed according to recognized, the message MUST be silently discarded.
Section 5.3.4.2.
If the message does contain a Nonce option, but the Nonce value is Otherwise, if the message does not contain a Nonce option, it MAY be
not recognized, the message MUST be silently dropped. considered as a non-solicited-for advertisement, and processed
according to Section 5.3.4.2.
If the message is accepted, the receiver SHOULD store the receive If the message is accepted, the receiver SHOULD store the receive
time of the message and the time stamp time in the message, as time of the message and the time stamp time in the message, as
specified in Section 5.3.4.2 specified in Section 5.3.4.2
5.3.4.2 Processing all other messages 5.3.4.2 Processing all other messages
Receivers SHOULD be configured with an allowed timestamp Delta value, Receivers SHOULD be configured with an allowed timestamp Delta value,
a "fuzz factor" for comparisons, and an allowed clock drift a "fuzz factor" for comparisons, and an allowed clock drift
parameter. The recommended default value for the allowed Delta is parameter. The recommended default value for the allowed Delta is
  Skipping to change at page 22, line 38:
This is called RDlast. This is called RDlast.
The time stamp in the last received, accepted SEND message. This The time stamp in the last received, accepted SEND message. This
is called TSlast. is called TSlast.
Receivers SHOULD then check the Timestamp field as follows: Receivers SHOULD then check the Timestamp field as follows:
o When a message is received from a new peer, i.e., one that is not o When a message is received from a new peer, i.e., one that is not
stored in the cache, the received timestamp, TSnew, is checked and stored in the cache, the received timestamp, TSnew, is checked and
the packet is accepted if the timestamp is recent enough with the packet is accepted if the timestamp is recent enough with
respect to the receival time of the packet, RDnew: respect to the reception time of the packet, RDnew:
-Delta < (RDnew - TSnew) < +Delta -Delta < (RDnew - TSnew) < +Delta
The RDnew and TSnew values SHOULD be stored into the cache as The RDnew and TSnew values SHOULD be stored into the cache as
RDlast and TSlast. RDlast and TSlast.
o If the timestamp is NOT within the boundaries but the message is a o If the timestamp is NOT within the boundaries but the message is a
Neighbor Solicitation message that should be responded to by the Neighbor Solicitation message that should be responded to by the
receiver, the receiver MAY respond to the message. However, if it receiver, the receiver MAY respond to the message. However, if it
does respond to the message, it MUST NOT create a neighbor cache does respond to the message, it MUST NOT create a neighbor cache
  Skipping to change at page 23, line 17:
against the previously received SEND message: against the previously received SEND message:
TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz
o If TSnew < TSlast, which is possible if packets arrive rapidly and o If TSnew < TSlast, which is possible if packets arrive rapidly and
out of order, TSlast MUST NOT be updated, i.e., the stored TSlast out of order, TSlast MUST NOT be updated, i.e., the stored TSlast
for a given node MUST NOT ever decrease. Otherwise TSlast SHOULD for a given node MUST NOT ever decrease. Otherwise TSlast SHOULD
be updated. Independent on whether TSlast is updated or not, be updated. Independent on whether TSlast is updated or not,
RDlast is updated in any case. RDlast is updated in any case.
5.4 Proxy Neighbor Discovery
The Target Address in Neighbor Advertisement is required to be equal
to the source address of the packet, except in the case of proxy
Neighbor Discovery. Proxy Neighbor Discovery is not supported by
this specification; it is planned to be specified in a future
document.
6. Authorization Delegation Discovery 6. Authorization Delegation Discovery
Several protocols, including the IPv6 Neighbor Discovery Protocol, Several protocols (NDP included) allow a node to automatically
allow a node to automatically configure itself based on information configure itself based on information it learns shortly after
it learns shortly after connecting to a new link. It is particularly connecting to a new link. It is particularly easy to configure
easy to configure "rogue" routers on an unsecured link, and it is "rogue" routers on an unsecured link, and it is particularly
particularly difficult for a node to distinguish between valid and difficult for a node to distinguish between valid and invalid sources
invalid sources of information, when the node needs this information of information, when the node needs this information before being
before being able to communicate with nodes outside of the link. able to communicate with nodes outside of the link.
Since the newly-connected node cannot communicate off-link, it cannot Since the newly-connected node cannot communicate off-link, it cannot
be responsible for searching information to help validating the be responsible for searching information to help validating the
router(s); however, given a chain of appropriately signed router(s); however, given a chain of appropriately signed
certificates, it can check someone else's search results and conclude certificates, it can check someone else's search results and conclude
that a particular message comes from an authorized source. In the that a particular message comes from an authorized source. In the
typical case, a router, which is already connected to beyond the typical case, a router, which is already connected to beyond the
link, can (if necessary) communicate with off-link nodes and link, can (if necessary) communicate with off-link nodes and
construct such a certificate chain. construct such a certificate chain.
  Skipping to change at page 24, line 36:
and routers to allow the host to learn a certificate chain with the and routers to allow the host to learn a certificate chain with the
assistance of the router. assistance of the router.
6.1 Certificate Format 6.1 Certificate Format
The certificate chain of a router terminates in a Router The certificate chain of a router terminates in a Router
Authorization Certificate that authorizes a specific IPv6 node to act Authorization Certificate that authorizes a specific IPv6 node to act
as a router. Because authorization chains are not a common practice as a router. Because authorization chains are not a common practice
in the Internet at the time this specification is being written, the in the Internet at the time this specification is being written, the
chain MUST consist of standard Public Key Certificates (PKC, in the chain MUST consist of standard Public Key Certificates (PKC, in the
sense of [20]). The certificates chain MUST start from the identity sense of [18]). The certificate chain MUST start from the identity
of a trust anchor that is shared by the host and the router. This of a trust anchor that is shared by the host and the router. This
allows the host to anchor trust for the router's public key in the allows the host to anchor trust for the router's public key in the
trust anchor. Note that there MAY be multiple certificates issued by trust anchor. Note that there MAY be multiple certificates issued by
a single trust anchor. a single trust anchor.
6.1.1 Router Authorization Certificate Profile 6.1.1 Router Authorization Certificate Profile
Router Authorization Certificates be X.509v3 certificates, as defined Router Authorization Certificates be X.509v3 certificates, as defined
in RFC 3280 [10], and MUST contain at least one instance of the X.509 in RFC 3280 [10], and MUST contain at least one instance of the X.509
extension for IP addresses, as defined in [11]. The parent extension for IP addresses, as defined in [11]. The parent
certificates in the certificate chain MUST contain one or more X.509 certificates in the certificate chain MUST contain one or more X.509
IP address extensions, back up to a trusted party (such as the user's IP address extensions, back up to a trusted party (such as the user's
ISP) that configured the original IP address space block for the ISP) that configured the original IP address space block for the
router in question, or delegated the right to do so for someone. The router in question, or delegated the right to do so for someone. The
certificates for intermediate delegating authorities MUST contain certificates for intermediate delegating authorities MUST contain
X.509 IP address extension(s) for subdelegations. The router's X.509 IP address extension(s) for subdelegations. The router's
certificate is signed by the delegating authority for the prefixes certificate is signed by the delegating authority for the prefixes
the router is authorized to to advertise. the router is authorized to to advertise.
The X.509 IP address extension MUST contain at least one The X.509 IP address extension MUST contain at least one
addressesOrRanges element that contains an addressPrefix element with addressesOrRanges element. This element MUST contain an
an IPv6 address prefix for a prefix the router or the intermediate addressPrefix element with an IPv6 address prefix for a prefix the
entity is authorized to advertise. If the entity is allowed to route router or the intermediate entity is authorized to advertise. If the
any prefix, the used IPv6 address prefix is the null prefix, 0/0. entity is allowed to route any prefix, the used IPv6 address prefix
The addressFamily element of the containing IPAddrBlocks sequence is the null prefix, 0/0. The addressFamily element of the containing
element MUST contain the IPv6 Address Family Identifier (0002), as IPAddrBlocks sequence element MUST contain the IPv6 Address Family
specified in [11] for IPv6 prefixes. Instead of an addressPrefix Identifier (0002), as specified in [11] for IPv6 prefixes. Instead
element, the addressesOrRange element MAY contain an addressRange of an addressPrefix element, the addressesOrRange element MAY contain
element for a range of prefixes, if more than one prefix is an addressRange element for a range of prefixes, if more than one
authorized. The X.509 IP address extension MAY contain additional prefix is authorized. The X.509 IP address extension MAY contain
IPv6 prefixes, expressed either as an addressPrefix or an additional IPv6 prefixes, expressed either as an addressPrefix or an
addressRange. addressRange.
A SEND node receiving a Router Authorization Certificate MUST first A SEND node receiving a Router Authorization Certificate MUST first
check whether the certificate's signature was generated by the check whether the certificate's signature was generated by the
delegating authority. Then the client MUST check whether all the delegating authority. Then the client MUST check whether all the
addressPrefix or addressRange entries in the router's certificate are addressPrefix or addressRange entries in the router's certificate are
contained within the address ranges in the delegating authority's contained within the address ranges in the delegating authority's
certificate, and whether the addressPrefix entries match any certificate, and whether the addressPrefix entries match any
addressPrefix entries in the delegating authority's certificate. If addressPrefix entries in the delegating authority's certificate. If
an addressPrefix or addressRange is not contained within the an addressPrefix or addressRange is not contained within the
delegating authority's prefixes or ranges, the client MAY attept to delegating authority's prefixes or ranges, the client MAY attempt to
take an intersection of the ranges/prefixes, and use that take an intersection of the ranges/prefixes, and use that
intersection. If the addressPrefix in the certificate is the null intersection. If the addressPrefix in the certificate is the null
prefix, 0/0, such an intersection SHOULD be used. (In that case the prefix, 0/0, such an intersection SHOULD be used. (In that case the
intersection is the parent prefix or range.) If the resulting intersection is the parent prefix or range.) If the resulting
intersection is empty, the client MUST NOT accept the certificate. intersection is empty, the client MUST NOT accept the certificate.
The above check SHOULD be done for all certificates in the chain The above check SHOULD be done for all certificates in the chain. If
received through DCA messages. If any of the checks fail, the client any of the checks fail, the client MUST NOT accept the certificate.
MUST NOT accept the certificate.
Since it is possible that some PKC certificates used with SEND do not Since it is possible that some PKC certificates used with SEND do not
immediately contain the X.509 IP address extension element, an immediately contain the X.509 IP address extension element, an
implementation MAY contain facilities that allow the prefix and range implementation MAY contain facilities that allow the prefix and range
checks to be relaxed. However, any such configuration options SHOULD checks to be relaxed. However, any such configuration options SHOULD
be off by default. That is, the system SHOULD have a default be off by default. That is, the system SHOULD have a default
configuration that requires rigorious prefix and range checks. configuration that requires rigorous prefix and range checks.
The following is an example of a certificate chain. Suppose that The following is an example of a certificate chain. Suppose that
ispgroup.com is the trust anchor. The host has this certificate for ispgroup.com is the trust anchor. The host has this certificate for
it: it:
Certificate 1: Certificate 1:
Issuer: isp_group.com Issuer: isp_group.com
Validity: Jan 1, 2004 through Dec 31, 2004 Validity: Jan 1, 2004 through Dec 31, 2004
Subject: isp_group.com Subject: isp_group.com
Extensions: Extensions:
IP address delegation extension: IP address delegation extension:
Prefixes: P1, ..., Pk Prefixes: P1, ..., Pk
... possibly other extensions ... ... possibly other extensions ...
... other certificate parameters ... ... other certificate parameters ...
The host attaches then to a linked served by router_x.isp_foo.com, When the host attaches then to a linked served by
and receives the following certificate chain: router_x.isp_foo.com, it receives the following certificate chain:
Certificate 2: Certificate 2:
Issuer: isp_group.com Issuer: isp_group.com
Validity: Jan 1, 2004 through Dec 31, 2004 Validity: Jan 1, 2004 through Dec 31, 2004
Subject: isp_foo.com Subject: isp_foo.com
Extensions: Extensions:
IP address delegation extension: IP address delegation extension:
Prefixes: Q1, ..., Qk Prefixes: Q1, ..., Qk
... possibly other extensions ... ... possibly other extensions ...
... other certificate parameters ... ... other certificate parameters ...
  Skipping to change at page 28, line 38:
An unused field. It MUST be initialized to zero by the sender An unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver. and MUST be ignored by the receiver.
Valid Options: Valid Options:
Trust Anchor Trust Anchor
One or more trust anchors that the client is willing to accept. One or more trust anchors that the client is willing to accept.
The first (or only) Trust Anchor option MUST contain a DER The first (or only) Trust Anchor option MUST contain a DER
Encoded X.501 Name; see Section 6.2.3. If there are more than Encoded X.501 Name; see Section 6.2.3. If there is more than
one Trust Anchor options, the options past the first one may one Trust Anchor option, the options past the first one may
contain any types of Trust Anchors. contain any types of Trust Anchors.
Future versions of this protocol may define new option types. Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize Receivers MUST silently ignore any options they do not recognize
and continue processing the message. All included options MUST and continue processing the message. All included options MUST
have a length that is greater than zero. have a length that is greater than zero.
ICMP length (derived from the IP length) MUST be 8 or more octets. ICMP length (derived from the IP length) MUST be 8 or more octets.
6.2.2 Delegation Chain Advertisement Message Format 6.2.2 Delegation Chain Advertisement Message Format
  Skipping to change at page 31, line 22:
Future versions of this protocol may define new option types. Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize Receivers MUST silently ignore any options they do not recognize
and continue processing the message. All included options MUST and continue processing the message. All included options MUST
have a length that is greater than zero. have a length that is greater than zero.
ICMP length (derived from the IP length) MUST be 8 or more octets. ICMP length (derived from the IP length) MUST be 8 or more octets.
6.2.3 Trust Anchor Option 6.2.3 Trust Anchor Option
The format of the Trust Anchor option is as described in the The format of the Trust Anchor option is described in the following:
following:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Name Type | Pad Length | | Type | Length | Name Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Name ... | Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows: Where the fields are as follows:
  Skipping to change at page 32, line 28:
"trustanchor.example.com". The name is stored as a string, in the "trustanchor.example.com". The name is stored as a string, in the
"preferred name syntax" DNS format, as specified in RFC 1034 [1] "preferred name syntax" DNS format, as specified in RFC 1034 [1]
Section 3.5. Additionally, the restrictions discussed in RFC 3280 Section 3.5. Additionally, the restrictions discussed in RFC 3280
[10] Section 4.2.1.7 apply. [10] Section 4.2.1.7 apply.
All systems MUST implement support the DER Encoded X.501 Name. All systems MUST implement support the DER Encoded X.501 Name.
Implementations MAY support the FQDN name type. Implementations MAY support the FQDN name type.
6.2.4 Certificate Option 6.2.4 Certificate Option
The format of the certificate option is as described in the The format of the certificate option is described in the following:
following:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Cert Type | Pad Length | | Type | Length | Cert Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate ... | Certificate ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows: Where the fields are as follows:
  Skipping to change at page 35, line 10:
backward-incompatible changes may use different Code values. The backward-incompatible changes may use different Code values. The
contents of any defined options that are not specified to be used contents of any defined options that are not specified to be used
with Delegation Chain Advertisement messages MUST be ignored and the with Delegation Chain Advertisement messages MUST be ignored and the
packet processed in the normal manner. The only defined options that packet processed in the normal manner. The only defined options that
may appear are the Certificate and Trust Anchor options. An may appear are the Certificate and Trust Anchor options. An
advertisement that passes the validity checks is called a "valid advertisement that passes the validity checks is called a "valid
advertisement". advertisement".
Hosts SHOULD store certificate chains retrieved in Delegation Chain Hosts SHOULD store certificate chains retrieved in Delegation Chain
Discovery messages if they start from an anchor trusted by the host. Discovery messages if they start from an anchor trusted by the host.
The certificates chains SHOULD be verified, as defined in Section The certificate chains SHOULD be verified, as defined in Section 6.1,
6.1, before storing them. Routers are required to send the before storing them. Routers MUST send the certificates one by one,
certificates one by one, starting from the trust anchor end of the starting from the trust anchor end of the chain. Except for
chain. Except for temporary purposes to allow for message loss and temporary purposes to allow for message loss and reordering, hosts
reordering, hosts SHOULD NOT store certificates received in a SHOULD NOT store certificates received in a Delegation Chain
Delegation Chain Advertisement unless they contain a certificate Advertisement unless they contain a certificate which can be
which can be immediately verified either to the trust anchor or to a immediately verified either to the trust anchor or to a certificate
certificate which has been verified earlier. which has been verified earlier.
Note that it may be useful to cache this information and implied Note that it may be useful to cache this information and implied
verification results for use over multiple attachments to the verification results for use over multiple attachments to the
network. network.
The host has a need to retrieve a delegation chain when a Router The host has a need to retrieve a delegation chain when a Router
Advertisement has been received with a public key that is not stored Advertisement has been received with a public key that is not stored
in the hosts' cache of certificates, or there is no authorization in the hosts' cache of certificates, or there is no authorization
delegation chain to the host's trust anchor. In these situations, delegation chain to the host's trust anchor. In these situations,
the host MAY transmit up to MAX_DCS_MESSAGES Delegation Chain the host MAY transmit up to MAX_DCS_MESSAGES Delegation Chain
  Skipping to change at page 35, line 50:
If two hosts want to establish trust with the DCS and DCA messages, If two hosts want to establish trust with the DCS and DCA messages,
the DCS message SHOULD be sent to the Solicited-Node multicast the DCS message SHOULD be sent to the Solicited-Node multicast
address of the receiver. The advertisements SHOULD be sent as address of the receiver. The advertisements SHOULD be sent as
specified above for routers. However, the exact details are left for specified above for routers. However, the exact details are left for
a future specification. a future specification.
When processing possible advertisements sent as responses to a When processing possible advertisements sent as responses to a
solicitation, the host MAY prefer to process first those solicitation, the host MAY prefer to process first those
advertisements with the same Identifier field value as in the advertisements with the same Identifier field value as in the
solicitation. This makes Denial-of-Service attacks against the solicitation. This makes Denial-of-Service attacks against the
mechanism harder (see Section 11.3). mechanism harder (see Section 9.3).
7. Securing Neighbor Discovery with SEND
This section describes how to use the mechanisms from Section 5,
Section 6, and the reference [12] in order to provide security for
Neighbor Discovery.
There is no requirement that nodes use both Secure Neighbor Discovery
(as described in this section) and Secure Router Discovery (as
described in Section 8. They MAY be used indepedently.
7.1 Neighbor Solicitation Messages
All Neighbor Solicitation messages are protected with SEND.
7.1.1 Sending Secure Neighbor Solicitations
Secure Neighbor Solicitation messages are sent as described in RFC
2461 and 2462, with the additional requirements as listed in the
following:
All Neighbor Solicitation messages sent MUST contain the Nonce,
Timestamp, CGA, and Signature options. The Signature option MUST
be constructed with the sender's key pair, using the configured
authorization method(s), and if applicable, using the trust anchor
and/or minSec value as configured.
7.1.2 Receiving Secure Neighbor Solicitations
Received Neighbor Solicitation messages are processed as described in
RFC 2461 and 2462, with the additional SEND-related requirements as
listed in the following:
Neighbor Solicitation messages received without the Nonce,
Timestamp, or Signature option MUST be silently discarded. The
Signature option MUST be constructed with the expected
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
7.2 Neighbor Advertisement Messages
All Neighbor Advertisement messages are protected with SEND.
7.2.1 Sending Secure Neighbor Advertisements
Secure Neighbor Advertisement messages are sent as described in RFC
2461 and 2462, with the additional requirements as listed in the
following:
All Neighbor Advertisement messages sent MUST be sent with the
Timestamp and Signature options and MAY be sent with the CGA
option. The Signature option MUST be constructed with the
sender's key pair, setting the authorization method and additional
information as configured.
Neighbor Advertisements sent in response to a Neighbor
Solicitation MUST additionally contain a copy of the Nonce option
included in the solicitation.
7.2.2 Receiving Secure Neighbor Advertisements
Received Neighbor Advertisement messages are processed as described
in RFC 2461 and 2462, with the additional SEND-related requirements
as listed in the following:
Any Neighbor Advertisement messages received without the Timestamp
or Signature options MUST be silently discarded. The Signature
option MUST be constructed with the expected authorization
method(s), the used key being within the configured minimum (and
maximum) allowable key size, and if applicable, using an
acceptable trust anchor and/or minSec value.
Received Neighbor Advertisements sent to a unicast destination
address without a Nonce option MUST be silently discarded.
7.3 Other Requirements 7. Addressing
Upon receiving a message for which the receiver has no certificate 7.1 CGA Addresses
chain to a trust anchor, the receiver MAY use Authorization
Delegation Discovery to learn the certificate chain of the peer.
Nodes that use stateless address autoconfiguration, SHOULD generate a Nodes that use stateless address autoconfiguration, SHOULD generate a
new CGA as specified in Section 4 of [12] for each new new CGA as specified in Section 4 of [12] for each new
autoconfiguration run. The nodes MAY continue to use the same public autoconfiguration run. The nodes MAY continue to use the same public
key and modifier, and start the process from Step 4. key and modifier, and start the process from Step 4.
By default, a SEND-enabled node SHOULD use only CGAs as its own By default, a SEND-enabled node SHOULD use only CGAs as its own
addresses. Other types of addresses MAY be used in testing, addresses. Other types of addresses MAY be used in testing,
diagnostics or other purposes. However, this document does not diagnostics or other purposes. However, this document does not
describe how to choose between different types of addresses for describe how to choose between different types of addresses for
different communications. A dynamic selection can be provided by an different communications. A dynamic selection can be provided by an
API, such as the one defined in [24]. API, such as the one defined in [22].
This specification does not address the protection of Neighbor 7.2 Redirect Addresses
Discovery packets for nodes that are configured with a static address
(e.g., PREFIX::1). Future certificate chain based authorization If the Target Address and Destination Address fields in the ICMP
specifications are needed for such nodes. Redirect message are equal, then this message is used to inform hosts
that a destination is in fact a neighbor. In this case the receiver
MUST verify that the given address falls within the range defined by
the router's certificate. Redirect messages failing this check MUST
be silently discarded.
Note that RFC 2461 rules prevent a bogus router from sending a
Redirect message when the host is not using the bogus router as a
default router.
7.3 Advertised Prefixes
The router's certificate defines the address range(s) that it is
allowed to advertise. Upon processing a Prefix Information option
within a Router Advertisement, the receiver MUST verify that the
prefix specified in this option falls within the range defined by the
certificate. Router Advertisements failing this check MUST be
silently discarded.
7.4 Limitations
This specification does not address the protection of NDP packets for
nodes that are configured with a static address (e.g., PREFIX::1).
Future certificate chain based authorization specifications are
needed for such nodes.
It is outside the scope of this specification to describe the use of It is outside the scope of this specification to describe the use of
trust anchor authorization between nodes with dynamically changing trust anchor authorization between nodes with dynamically changing
addresses. Such dynamically changing addresses may be the result of addresses. Such dynamically changing addresses may be the result of
stateful or stateless address autoconfiguration, or through the use stateful or stateless address autoconfiguration, or through the use
of RFC 3041 [19] addresses. If the CGA method is not used, nodes of RFC 3041 [17] addresses. If the CGA method is not used, nodes
would be required to exchange certificate chains that terminate in a would be required to exchange certificate chains that terminate in a
certificate authorizing a node to use an IP address having a certificate authorizing a node to use an IP address having a
particular interface identifier. This specification does not specify particular interface identifier. This specification does not specify
the format of such certificates, since there are currently a few the format of such certificates, since there are currently a few
cases where such certificates are required by the link layer and it cases where such certificates are required by the link layer and it
is up to the link layer to provide certification for the interface is up to the link layer to provide certification for the interface
identifier. This may be the subject of a future specification. It identifier. This may be the subject of a future specification. It
is also outside the scope of this specification to describe how is also outside the scope of this specification to describe how
stateful address autoconfiguration works with the CGA method. stateful address autoconfiguration works with the CGA method.
8. Securing Router Discovery with SEND The Target Address in Neighbor Advertisement is required to be equal
to the source address of the packet, except in the case of proxy
This section describes how to use the mechanisms from Section 5, Neighbor Discovery. Proxy Neighbor Discovery is not supported by
Section 6, and the reference [12] in order to provide security for this specification; it is planned to be specified in a future
Router Discovery. document.
8.1 Router Solicitation Messages
All Router Solicitation messages are protected with SEND.
8.1.1 Sending Secure Router Solicitations
Secure Router Solicitation messages are sent as described in RFC
2461, with the additional requirements as listed in the following:
Router Solicitation messages sent with an unspecified source
address MUST have the Nonce and Timestamp options.
Other Router Solicitations MUST have the Nonce, Timestamp, CGA,
and Signature options. The Signature option MUST be configured
with the sender's key pair, setting the authorization method and
additional information as is configured.
8.1.2 Receiving Secure Router Solicitations
Received Router Solicitation messages are processed as described in
RFC 2461, with the additional SEND-related requirements as listed in
the following:
Router Solicitation message sent with an unspecified source
address and without the Nonce or Timestamp options MUST be
silently discarded.
Router Solicitation messages received with another type of source
address but without the Nonce, Timestamp, or Signature options
MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
8.2 Router Advertisement Messages
All Router Advertisement messages are protected with SEND.
8.2.1 Sending Secure Router Advertisements
Secure Router Advertisement messages are sent as described in RFC
2461, with the additional requirements as listed in the following:
All Router Advertisement messages sent MUST contain a Timestamp
and Signature options. The Signature option MUST be configured to
protect the advertisement with the trust anchor authorization
method and MAY be configured to additionally protect it with the
CGA authorization method.
Router Advertisements sent in response to a Router Solicitation
MUST contain a copy of the Nonce option included in the
solicitation.
8.2.2 Receiving Secure Router Advertisements
Received Router Advertisement messages are processed as described in
RFC 2461, with the additional SEND-related requirements as listed in
the following:
Router Advertisement messages received without the Timestamp and
Signature options MUST be silently discarded.
Received Router Advertisements sent to a unicast destination
address without a Nonce option MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
The configured authorization methods MUST include the trust anchor
authorization method, and MAY be additionally configured to
require CGA authorization.
The sender's certificate defines the address range(s) that this
router is allowed to advertise. Upon processing a Prefix
Information option within a Router Advertisement, the receiver
MUST verify that the prefix specified in this option falls within
the range defined by the certificate. Router Advertisements
failing this check MUST be silently discarded.
8.3 Redirect Messages
All Redirect messages are protected with SEND.
8.3.1 Sending Redirects
Secure Redirect messages are sent as described in RFC 2461, with the
additional requirements as listed in the following:
All Redirect messages sent MUST contain the Timestamp and
Signature options. The Signature option MUST be configured to use
the trust anchor authorization method, and MAY be additionally
configured to use the CGA method.
8.3.2 Receiving Redirects
Received Redirect messages are processed as described in RFC 2461,
with the additional SEND-related requirements as listed in the
following:
Redirect messages received without the Timestamp or Signature
options MUST be silently discarded.
The Signature option MUST be constructed with the configured
authorization method(s), the used key being within the configured
minimum (and maximum) allowable key size, and if applicable, using
an acceptable trust anchor and/or minSec value.
The configured authorization methods MUST include the trust anchor
authorization method, and MAY be additionally configured to
require CGA authorization.
Note that RFC 2461 rules already prevent a bogus router from
sending a Redirect message when the host is not using the bogus
router as a default router.
If the Target Address and Destination Address fields in the ICMP
Redirect message are equal, then this message is used to inform
hosts that a destination is in fact a neighbor. In this case the
receiver MUST verify that the given address falls within the range
defined by the router's certificate. Redirect messages failing
this check MUST be silently discarded.
8.4 Other Requirements
Hosts SHOULD use Authorization Delegation Discovery to learn the
certificate chain of their default router (or peer host), as
explained in Section 6. The receipt of a protected Router
Advertisement message for which no router Authorization Certificate
and certificate chain is available triggers Authorization Delegation
Discovery.
9. Co-Existence of SEND and non-SEND nodes 8. Transition Issues
During the transition to secure links or as a policy consideration, During the transition to secure links or as a policy consideration,
network operators may want to run a particular link with a mixture of network operators may want to run a particular link with a mixture of
secure and insecure nodes. Nodes that support SEND SHOULD support secure and insecure nodes. Nodes that support SEND SHOULD support
the use of SEND and the legacy Neighbor Discovery Protocol at the the use of SEND and the legacy NDP at the same time.
same time.
In a mixed environment, SEND nodes receive both secure and insecure In a mixed environment, SEND nodes receive both secure and insecure
messages but give priority to "secured" ones. Here, the "secured" messages but give priority to "secured" ones. Here, the "secured"
messages are ones that contain a valid signature option, as specified messages are ones that contain a valid signature option, as specified
above, and "insecure" messages are ones that contain no signature above, and "insecure" messages are ones that contain no signature
option. option.
SEND nodes send only secured messages. Legacy Neighbor Discovery SEND nodes send only secured messages. Legacy Neighbor Discovery
nodes will obviously send only insecure messages. Per RFC 2461 [7], nodes will obviously send only insecure messages. Per RFC 2461 [7],
such nodes will ignore the unknown options and will treat secured such nodes will ignore the unknown options and will treat secured
messages in the same way as they treat insecure ones. Secured and messages in the same way as they treat insecure ones. Secured and
insecure nodes share the same network resources, such as prefixes and insecure nodes share the same network resources, such as prefixes and
address spaces. address spaces.
In a mixed environment SEND nodes follow the protocols defined in RFC In a mixed environment SEND nodes follow the protocols defined in RFC
2461 and RFC 2462 with the following exceptions: 2461 and RFC 2462 with the following exceptions:
All solicitations sent by SEND nodes MUST be secured. o All solicitations sent by SEND nodes MUST be secured.
Unsolicited advertisements sent by a SEND node MUST be secured. o Unsolicited advertisements sent by a SEND node MUST be secured.
A SEND node MUST send a secured advertisement in response to a o A SEND node MUST send a secured advertisement in response to a
secured solicitation. Advertisements sent in response to an secured solicitation. Advertisements sent in response to an
insecure solicitation MUST be secured as well, but MUST NOT insecure solicitation MUST be secured as well, but MUST NOT
contain the Nonce option. contain the Nonce option.
A SEND node that uses the CGA authorization method for protecting o A SEND node that uses the CGA authorization method for protecting
Neighbor Solicitations SHOULD perform Duplicate Address Detection Neighbor Solicitations SHOULD perform Duplicate Address Detection
as follows. If Duplicate Address Detection indicates the as follows. If Duplicate Address Detection indicates the
tentative address is already in use, generate a new tentative CGA tentative address is already in use, generate a new tentative CGA
address. If after 3 consecutive attempts no non-unique address address. If after 3 consecutive attempts no non-unique address
was generated, log a system error and give up attempting to was generated, log a system error and give up attempting to
generate an address for that interface. generate an address for that interface.
When performing Duplicate Address Detection for the first When performing Duplicate Address Detection for the first
tentative address, accept both secured and insecure Neighbor tentative address, accept both secured and insecure Neighbor
Advertisements and Solicitations received as response to the Advertisements and Solicitations received as response to the
Neighbor Solicitations. When performing Duplicate Address Neighbor Solicitations. When performing Duplicate Address
Detection for the second or third tentative address, ignore Detection for the second or third tentative address, ignore
insecure Neighbor Advertisements and Solicitations. insecure Neighbor Advertisements and Solicitations.
The node SHOULD have a configuration option that causes it to o The node SHOULD have a configuration option that causes it to
ignore insecure advertisements even when performing Duplicate ignore insecure advertisements even when performing Duplicate
Address Detection for the first tentative address. This Address Detection for the first tentative address. This
configuration option SHOULD be disabled by default. This is configuration option SHOULD be disabled by default. This is
recovery mechanism, in case attacks against the first address recovery mechanism, in case attacks against the first address
become common. become common.
The Neighbor Cache, Prefix List and Default Router list entries o The Neighbor Cache, Prefix List and Default Router list entries
MUST have a secured/insecure flag that indicates whether the MUST have a secured/insecure flag that indicates whether the
message that caused the creation or last update of the entry was message that caused the creation or last update of the entry was
secured or insecure. Received insecure messages MUST NOT cause secured or insecure. Received insecure messages MUST NOT cause
changes to existing secured entries in the Neighbor Cache, Prefix changes to existing secured entries in the Neighbor Cache, Prefix
List or Default Router List. Received secured messages cause an List or Default Router List. Received secured messages cause an
update of the matching entries and flagging of them as secured. update of the matching entries and flagging of them as secured.
The conceptual sending algorithm is modified so that an insecure o The conceptual sending algorithm is modified so that an insecure
router is selected only if there is no reachable SEND router for router is selected only if there is no reachable SEND router for
the prefix. That is, the algorithm for selecting a default router the prefix. That is, the algorithm for selecting a default router
favors reachable SEND routers over reachable non-SEND ones. favors reachable SEND routers over reachable non-SEND ones.
A SEND node SHOULD have a configuration option that causes it to o A SEND node SHOULD have a configuration option that causes it to
ignore all insecure Neighbor Solicitation and Advertisement, ignore all insecure Neighbor Solicitation and Advertisement,
Router Solicitation and Advertisement, and Redirect messages. Router Solicitation and Advertisement, and Redirect messages.
This can be used to enforce SEND-only networks. This can be used to enforce SEND-only networks.
10. Performance Considerations 9. Security Considerations
The computations related to the Signature option are computationally
relatively expensive. In the application which Signature option has
been designed for, however, the nodes typically have the need to
perform only a few signature operations as they enter a link, and a
few operations as they find a new on-link peer with which to
communicate.
Routers are required to perform a larger number of operations,
particularly when the frequency of router advertisements is high due
to mobility requirements. Still, the number of required signature
operations is on the order of a few dozen ones per second, some of
which can be precomputed as discussed below. A large number of
router solicitations may cause higher demand for performing
asymmetric operations, although RFC 2461 limits the rate at which
responses to solicitations can be sent.
Signatures can be precomputed for unsolicited (multicast) Neighbor
and Router Advertisements. Typically, solicited advertisements are
sent to the unicast address from which the solicitation was sent.
Given that the IPv6 header is covered by the signature, it is not
possible to precompute solicited-for advertisements.
11. Security Considerations 9.1 Threats to the Local Link Not Covered by SEND
11.1 Threats to the Local Link Not Covered by SEND SEND does not provide confidentiality for NDP communications.
SEND does not compensate for an insecure link layer. For instance, SEND does not compensate for an insecure link layer. For instance,
there is no assurance that payload packets actually come from the there is no assurance that payload packets actually come from the
same peer that the Neighbor Discovery protocol was run against. same peer that the NDP was run against.
SEND does not provide confidentiality for Neighbor Discovery
communications.
There may be no cryptographic binding in SEND between the link layer There may be no cryptographic binding in SEND between the link layer
frame address and the IPv6 address. On an insecure link layer that frame address and the IPv6 address. On an insecure link layer that
allows nodes to spoof the link layer address of other nodes, an allows nodes to spoof the link layer address of other nodes, an
attacker could disrupt IP service by sending out a Neighbor attacker could disrupt IP service by sending out a Neighbor
Advertisement having the source address on the link layer frame of a Advertisement having the source address on the link layer frame of a
victim, a valid CGA address and a valid signature corresponding to victim, a valid CGA address and a valid signature corresponding to
itself, and a Target Link-layer Address extension corresponding to itself, and a Target Link-layer Address extension corresponding to
the victim. The attacker could then proceed to cause a traffic the victim. The attacker could then proceed to cause a traffic
stream to bombard the victim in a DoS attack. This attack cannot be stream to bombard the victim in a DoS attack. This attack cannot be
prevented just by securing the link layer alone. prevented just by securing the link layer.
Even on a secure link layer, SEND does not require that the addresses Even on a secure link layer, SEND does not require that the addresses
on the link layer and Neighbor Advertisements correspond to each on the link layer and Neighbor Advertisements correspond to each
other. However, it is RECOMMENDED that such checks be performed other. However, it is RECOMMENDED that such checks be performed
where this is possible on the given link layer technology. where this is possible on the given link layer technology.
Prior to participating in Neighbor Discovery and Duplicate Address Prior to participating in Neighbor Discovery and Duplicate Address
Detection, nodes must subscribe to the link-scoped All-Nodes Detection, nodes must subscribe to the link-scoped All-Nodes
Multicast Group and the Solicited-Node Multicast Group for the Multicast Group and the Solicited-Node Multicast Group for the
address that they are claiming for their addresses; RFC 2461 [7]. address that they are claiming for their addresses; RFC 2461 [7].
Subscribing to a multicast group requires that the nodes use MLD Subscribing to a multicast group requires that the nodes use MLD
[18]. MLD contains no provision for security. An attacker could [16]. MLD contains no provision for security. An attacker could
send an MLD Done message to unsubscribe a victim from the send an MLD Done message to unsubscribe a victim from the
Solicited-Node Multicast address. However, the victim should be able Solicited-Node Multicast address. However, the victim should be able
to detect such an attack because the router sends a to detect such an attack because the router sends a
Multicast-Address-Specific Query to determine whether any listeners Multicast-Address-Specific Query to determine whether any listeners
are still on the address, at which point the victim can respond to are still on the address, at which point the victim can respond to
avoid being dropped from the group. This technique will work if the avoid being dropped from the group. This technique will work if the
router on the link has not been compromised. Other attacks using MLD router on the link has not been compromised. Other attacks using MLD
are possible, but they primarily lead to extraneous (but not are possible, but they primarily lead to extraneous (but not
overwhelming) traffic. overwhelming) traffic.
11.2 How SEND Counters Threats to Neighbor Discovery 9.2 How SEND Counters Threats to NDP
The SEND protocol is designed to counter the threats to IPv6 Neighbor The SEND protocol is designed to counter the threats to NDP, as
Discovery, as outlined in [27]. The following subsections contain a outlined in [25]. The following subsections contain a regression of
regression of the SEND protocol against the threats, to illustrate the SEND protocol against the threats, to illustrate what aspects of
what aspects of the protocol counter each threat. the protocol counter each threat.
11.2.1 Neighbor Solicitation/Advertisement Spoofing 9.2.1 Neighbor Solicitation/Advertisement Spoofing
This threat is defined in Section 4.1.1 of [27]. The threat is that This threat is defined in Section 4.1.1 of [25]. The threat is that
a spoofed message may cause a false entry in a node's Neighbor Cache. a spoofed message may cause a false entry in a node's Neighbor Cache.
There are two cases: There are two cases:
1. Entries made as a side effect of a Neighbor Solicitation or 1. Entries made as a side effect of a Neighbor Solicitation or
Router Solicitation. A router receiving a Router Solicitation Router Solicitation. A router receiving a Router Solicitation
with a firm IPv6 source address and a Target Link-Layer Address with a firm IPv6 source address and a Target Link-Layer Address
extension inserts an entry for the IPv6 address into its Neighbor extension inserts an entry for the IPv6 address into its Neighbor
Cache. Also, a node performing Duplicate Address Detection (DAD) Cache. Also, a node performing Duplicate Address Detection (DAD)
that receives a Neighbor Solicitation for the same address that receives a Neighbor Solicitation for the same address
regards the situation as a collision and ceases to solicit for regards the situation as a collision and ceases to solicit for
the address. the address.
In either case, SEND counters these treats by requiring the In either case, SEND counters these treats by requiring the
Signature and CGA options to be present in such solicitations. Signature and CGA options to be present in such solicitations.
As discussed in Section 8.1, SEND nodes preferably send Router SEND nodes can send Router Solicitation messages with a CGA
Solicitations with a CGA source address, which the router can source address and a CGA option, which the router can verify, so
verify, so the Neighbor Cache binding is correct. If a SEND node the Neighbor Cache binding is correct. If a SEND node must send
must send a Router Solicitation with the unspecified address, the a Router Solicitation with the unspecified address, the router
router will not update its Neighbor Cache, as per RFC 2461. will not update its Neighbor Cache, as per RFC 2461.
2. Entries made as a result of a Neighbor Advertisement message. 2. Entries made as a result of a Neighbor Advertisement message.
SEND counters this threat by requiring the Signature and CGA SEND counters this threat by requiring the Signature and CGA
options to be present in these advertisements. options to be present in these advertisements.
See also Section 11.2.5, below, for discussion about replay See also Section 9.2.5, below, for discussion about replay protection
protection and timestamps. and timestamps.
11.2.2 Neighbor Unreachability Detection Failure 9.2.2 Neighbor Unreachability Detection Failure
This attack is described in Section 4.1.2 of [27]. SEND counters This attack is described in Section 4.1.2 of [25]. SEND counters
this attack by requiring a node responding to Neighbor Solicitations this attack by requiring a node responding to Neighbor Solicitations
sent as NUD probes to include a Signature option and proof of sent as NUD probes to include a Signature option and proof of
authorization to use the interface identifier in the address being authorization to use the interface identifier in the address being
probed. If these prerequisites are not met, the node performing NUD probed. If these prerequisites are not met, the node performing NUD
discards the responses. discards the responses.
11.2.3 Duplicate Address Detection DoS Attack 9.2.3 Duplicate Address Detection DoS Attack
This attack is described in Section 4.1.3 of [27]. SEND counters This attack is described in Section 4.1.3 of [25]. SEND counters
this attack by requiring the Neighbor Advertisements sent as this attack by requiring the Neighbor Advertisements sent as
responses to DAD to include a Signature option and proof of responses to DAD to include a Signature option and proof of
authorization to use the interface identifier in the address being authorization to use the interface identifier in the address being
tested. If these prerequisites are not met, the node performing DAD tested. If these prerequisites are not met, the node performing DAD
discards the responses. discards the responses.
When a SEND node is used on a link that also connects to non-SEND When a SEND node is used on a link that also connects to non-SEND
nodes, the SEND node ignores any insecure Neighbor Solicitations or nodes, the SEND node ignores any insecure Neighbor Solicitations or
Advertisements that may be send by the non-SEND nodes. This protects Advertisements that may be send by the non-SEND nodes. This protects
the SEND node from DAD DoS attacks by non-SEND nodes or attackers the SEND node from DAD DoS attacks by non-SEND nodes or attackers
simulating to non-SEND nodes, at the cost of a potential address simulating to non-SEND nodes, at the cost of a potential address
collision between a SEND node and non-SEND node. The probability and collision between a SEND node and non-SEND node. The probability and
effects of such an address collision are discussed in [12]. effects of such an address collision are discussed in [12].
11.2.4 Router Solicitation and Advertisement Attacks 9.2.4 Router Solicitation and Advertisement Attacks
These attacks are described in Sections 4.2.1, 4.2.4, 4.2.5, 4.2.6, These attacks are described in Sections 4.2.1, 4.2.4, 4.2.5, 4.2.6,
and 4.2.7 of [27]. SEND counters these attacks by requiring Router and 4.2.7 of [25]. SEND counters these attacks by requiring Router
Advertisements to contain a Signature option, and that the signature Advertisements to contain a Signature option, and that the signature
is calculated using the public key of a node that can prove its is calculated using the public key of a node that can prove its
authorization to route the subnet prefixes contained in any Prefix authorization to route the subnet prefixes contained in any Prefix
Information Options. The router proves its authorization by showing Information Options. The router proves its authorization by showing
a certificate containing the specific prefix or the indication that a certificate containing the specific prefix or the indication that
the router is allowed to route any prefix. A Router Advertisement the router is allowed to route any prefix. A Router Advertisement
without these protections is dropped. without these protections is discarded.
SEND does not protect against brute force attacks on the router, such SEND does not protect against brute force attacks on the router, such
as DoS attacks, or compromise of the router, as described in Sections as DoS attacks, or compromise of the router, as described in Sections
4.4.2 and 4.4.3 of [27]. 4.4.2 and 4.4.3 of [25].
11.2.5 Replay Attacks 9.2.5 Replay Attacks
This attack is described in Section 4.3.1 of [27]. SEND protects This attack is described in Section 4.3.1 of [25]. SEND protects
against attacks in Router Solicitation/Router Advertisement and against attacks in Router Solicitation/Router Advertisement and
Neighbor Solicitation/Neighbor Advertisement transactions by Neighbor Solicitation/Neighbor Advertisement transactions by
including a Nonce option in the solicitation and requiring the including a Nonce option in the solicitation and requiring the
advertisement to include a matching option. Together with the advertisement to include a matching option. Together with the
signatures this forms a challenge-response protocol. SEND protects signatures this forms a challenge-response protocol. SEND protects
against attacks from unsolicited messages such as Neighbor against attacks from unsolicited messages such as Neighbor
Advertisements, Router Advertisements, and Redirects by including a Advertisements, Router Advertisements, and Redirects by including a
Timestamp option. A window of vulnerability for replay attacks Timestamp option. A window of vulnerability for replay attacks
exists until the timestamp expires. exists until the timestamp expires.
When timestamps are used, SEND nodes are protected against replay When timestamps are used, SEND nodes are protected against replay
attacks as long as they cache the state created by the message attacks as long as they cache the state created by the message
containing the timestamp. The cached state allows the node to containing the timestamp. The cached state allows the node to
protect itself against replayed messages. However, once the node protect itself against replayed messages. However, once the node
flushes the state for whatever reason, an attacker can re-create the flushes the state for whatever reason, an attacker can re-create the
state by replaying an old message while the timestamp is still valid. state by replaying an old message while the timestamp is still valid.
Since most SEND nodes are likely to use fairly coarse grained Since most SEND nodes are likely to use fairly coarse grained
timestamps, as explained in Section 5.3.1, this may affect some timestamps, as explained in Section 5.3.1, this may affect some
nodes. nodes.
11.2.6 Neighbor Discovery DoS Attack 9.2.6 Neighbor Discovery DoS Attack
This attack is described in Section 4.3.2 of [27]. In this attack, This attack is described in Section 4.3.2 of [25]. In this attack,
the attacker bombards the router with packets for fictitious the attacker bombards the router with packets for fictitious
addresses on the link, causing the router to busy itself with addresses on the link, causing the router to busy itself with
performing Neighbor Solicitations for addresses that do not exist. performing Neighbor Solicitations for addresses that do not exist.
SEND does not address this threat because it can be addressed by SEND does not address this threat because it can be addressed by
techniques such as rate limiting Neighbor Solicitations, restricting techniques such as rate limiting Neighbor Solicitations, restricting
the amount of state reserved for unresolved solicitations, and clever the amount of state reserved for unresolved solicitations, and clever
cache management. These are all techniques involved in implementing cache management. These are all techniques involved in implementing
Neighbor Discovery on the router. Neighbor Discovery on the router.
11.3 Attacks against SEND Itself 9.3 Attacks against SEND Itself
The CGAs have a 59-bit hash value. The security of the CGA mechanism The CGAs have a 59-bit hash value. The security of the CGA mechanism
has been discussed in [12]. has been discussed in [12].
Some Denial-of-Service attacks against NDP and SEND itself remain. Some Denial-of-Service attacks against NDP and SEND itself remain.
For instance, an attacker may try to produce a very high number of For instance, an attacker may try to produce a very high number of
packets that a victim host or router has to verify using asymmetric packets that a victim host or router has to verify using asymmetric
methods. While safeguards are required to prevent an excessive use methods. While safeguards are required to prevent an excessive use
of resources, this can still render SEND non-operational. of resources, this can still render SEND non-operational.
When CGA protection is used, SEND deals with the DoS attacks using When CGA protection is used, SEND deals with the DoS attacks using
the verification process described in Section 5.2.2. In this the verification process described in Section 5.2.2. In this
process, a simple hash verification of the CGA property of the process, a simple hash verification of the CGA property of the
address is performed first before performing the more expensive address is performed before performing the more expensive signature
signature verification. verification.
When trust anchors and certificates are used for address validation When trust anchors and certificates are used for address validation
in SEND, the defenses are not quite as effective. Implementations in SEND, the defenses are not quite as effective. Implementations
SHOULD track the resources devoted to the processing of packets SHOULD track the resources devoted to the processing of packets
received with the Signature option, and start selectively dropping received with the Signature option, and start selectively discarding
packets if too many resources are spent. Implementations MAY also packets if too many resources are spent. Implementations MAY also
first drop packets that are not protected with CGA. first discard packets that are not protected with CGA.
The Authorization Delegation Discovery process may also be vulnerable The Authorization Delegation Discovery process may also be vulnerable
to Denial-of-Service attacks. An attack may target a router by to Denial-of-Service attacks. An attack may target a router by
requesting a large number of delegation chains to be discovered for requesting a large number of delegation chains to be discovered for
different trust anchors. Routers SHOULD defend against such attacks different trust anchors. Routers SHOULD defend against such attacks
by caching discovered information (including negative responses) and by caching discovered information (including negative responses) and
by limiting the number of different discovery processes they engage by limiting the number of different discovery processes they engage
in. in.
Attackers may also target hosts by sending a large number of Attackers may also target hosts by sending a large number of
unnecessary certificate chains, forcing hosts to spend useless memory unnecessary certificate chains, forcing hosts to spend useless memory
and verification resources for them. Hosts can defend against such and verification resources for them. Hosts can defend against such
attacks by limiting the amount of resources devoted to the attacks by limiting the amount of resources devoted to the
certificate chains and their verification. Hosts SHOULD also certificate chains and their verification. Hosts SHOULD also
prioritize advertisements that sent as a response to their prioritize advertisements that sent as a response to their
solicitations above unsolicited advertisements. solicitations above unsolicited advertisements.
12. Protocol Constants 10. Protocol Constants
Host constants: Host constants:
MAX_DCS_MESSAGES 3 transmissions MAX_DCS_MESSAGES 3 transmissions
DCS_INTERVAL 4 seconds DCS_INTERVAL 4 seconds
Router constants: Router constants:
MAX_DCA_RATE 10 times per second MAX_DCA_RATE 10 times per second
13. IANA Considerations 11. IANA Considerations
This document defines two new ICMP message types, used in This document defines two new ICMP message types, used in
Authorization Delegation Discovery. These messages must be assigned Authorization Delegation Discovery. These messages must be assigned
ICMPv6 type numbers from the informational message range: ICMPv6 type numbers from the informational message range:
o The Delegation Chain Solicitation message, described in Section o The Delegation Chain Solicitation message, described in Section
6.2.1. 6.2.1.
o The Delegation Chain Advertisement message, described in Section o The Delegation Chain Advertisement message, described in Section
6.2.2. 6.2.2.
This document defines six new Neighbor Discovery Protocol [7] This document defines six new Neighbor Discovery Protocol [7]
options, which must be assigned Option Type values within the option options, which must be assigned Option Type values within the option
numbering space for Neighbor Discovery Protocol messages: numbering space for Neighbor Discovery Protocol messages:
o The Trust Anchor option, described in Section 6.2.3.
o The Certificate option, described in Section 6.2.4.
o The CGA option, described in Section 5.1. o The CGA option, described in Section 5.1.
o The Signature option, described in Section 5.2. o The Signature option, described in Section 5.2.
o The Timestamp option, described in Section 5.3.1. o The Timestamp option, described in Section 5.3.1.
o The Nonce option, described in Section 5.3.2. o The Nonce option, described in Section 5.3.2.
This document defines a new 128-bit CGA Message Type [12] value, o The Trust Anchor option, described in Section 6.2.3.
0xXXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX (To be generated randomly).
XXX: Use existing name spaces for these? o The Certificate option, described in Section 6.2.4.
This document defines a new 128-bit value under the CGA Message Type
[12] namespace, 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08.
This document defines a new name space for the Name Type field in the This document defines a new name space for the Name Type field in the
Trust Anchor option. Future values of this field can be allocated Trust Anchor option. Future values of this field can be allocated
using standards action [6]. using standards action [6]. The current values for this field are:
1 DER Encoded X.501 Name
2 FQDN
Another new name space is allocated for the Cert Type field in the Another new name space is allocated for the Cert Type field in the
Certificate option. Future values of this field can be allocated Certificate option. Future values of this field can be allocated
using standards action [6]. using standards action [6]. The current values for this field are:
1 X.509v3 Certificate
Normative References Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD [1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987. 13, RFC 1034, November 1987.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Kent, S. and R. Atkinson, "Security Architecture for the [3] Kent, S. and R. Atkinson, "Security Architecture for the
  Skipping to change at page 54, line 7:
[13] RSA Laboratories, "RSA Encryption Standard, Version 2.1", PKCS [13] RSA Laboratories, "RSA Encryption Standard, Version 2.1", PKCS
1, November 2002. 1, November 2002.
[14] National Institute of Standards and Technology, "Secure Hash [14] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-1, April 1995, <http:// Standard", FIPS PUB 180-1, April 1995, <http://
www.itl.nist.gov/fipspubs/fip180-1.htm>. www.itl.nist.gov/fipspubs/fip180-1.htm>.
Informative References Informative References
[15] Postel, J., "Internet Control Message Protocol", STD 5, RFC [15] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
792, September 1981.
[16] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, RFC
826, November 1982.
[17] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998. RFC 2409, November 1998.
[18] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener [16] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999. Discovery (MLD) for IPv6", RFC 2710, October 1999.
[19] Narten, T. and R. Draves, "Privacy Extensions for Stateless [17] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001. Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[20] Farrell, S. and R. Housley, "An Internet Attribute Certificate [18] Farrell, S. and R. Housley, "An Internet Attribute Certificate
Profile for Authorization", RFC 3281, April 2002. Profile for Authorization", RFC 3281, April 2002.
[21] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) [19] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003. Addressing Architecture", RFC 3513, April 2003.
[22] Arkko, J., "Effects of ICMPv6 on IKE and IPsec Policies", [20] Arkko, J., "Effects of ICMPv6 on IKE and IPsec Policies",
draft-arkko-icmpv6-ike-effects-02 (work in progress), March draft-arkko-icmpv6-ike-effects-02 (work in progress), March
2003. 2003.
[23] Arkko, J., "Manual SA Configuration for IPv6 Link Local [21] Arkko, J., "Manual SA Configuration for IPv6 Link Local
Messages", draft-arkko-manual-icmpv6-sas-01 (work in progress), Messages", draft-arkko-manual-icmpv6-sas-01 (work in progress),
June 2002. June 2002.
[24] Nordmark, E., Chakrabarti, S. and J. Laganier, "IPv6 Socket API [22] Nordmark, E., Chakrabarti, S. and J. Laganier, "IPv6 Socket API
for Address Selection", draft-chakrabarti-ipv6-addrselect-02 for Address Selection", draft-chakrabarti-ipv6-addrselect-02
(work in progress), October 2003. (work in progress), October 2003.
[25] Droms, R., "Dynamic Host Configuration Protocol for IPv6 [23] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002. November 2002.
[26] Kent, S., "IP Encapsulating Security Payload (ESP)", [24] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-06 (work in progress), July 2003. draft-ietf-ipsec-esp-v3-06 (work in progress), July 2003.
[27] Nikander, P., "IPv6 Neighbor Discovery trust models and [25] Nikander, P., "IPv6 Neighbor Discovery trust models and
threats", draft-ietf-send-psreq-00 (work in progress), October threats", draft-ietf-send-psreq-00 (work in progress), October
2002. 2002.
[28] International Organization for Standardization, "The Directory [26] International Organization for Standardization, "The Directory
- Authentication Framework", ISO Standard X.509, 2000. - Authentication Framework", ISO Standard X.509, 2000.
[29] Institute of Electrical and Electronics Engineers, "Local and [27] Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access Control", Metropolitan Area Networks: Port-Based Network Access Control",
IEEE Standard 802.1X, September 2001. IEEE Standard 802.1X, September 2001.
Authors' Addresses Authors' Addresses
Jari Arkko Jari Arkko
Ericsson Ericsson
Jorvas 02420 Jorvas 02420
Finland Finland
  Skipping to change at page 57, line 8:
Ericsson Ericsson
Jorvas 02420 Jorvas 02420
Finland Finland
EMail: Pekka.Nikander@nomadiclab.com EMail: Pekka.Nikander@nomadiclab.com
Appendix A. Contributors Appendix A. Contributors
Tuomas Aura contributed the transition mechanism specification in Tuomas Aura contributed the transition mechanism specification in
Section 9. Section 8.
Appendix B. Acknowledgements Appendix B. Acknowledgments
The authors would like to thank Tuomas Aura, Erik Nordmark, Gabriel The authors would like to thank Tuomas Aura, Erik Nordmark, Gabriel
Montenegro, Pasi Eronen, and Francis Dupont for interesting Montenegro, Pasi Eronen, and Francis Dupont for interesting
discussions in this problem space. discussions in this problem space.
Appendix C. Cache Management Appendix C. Cache Management
In this section we outline a cache management algorithm that allows a In this section we outline a cache management algorithm that allows a
node to remain partially functional even under a cache filling DoS node to remain partially functional even under a cache filling DoS
attack. This appendix is informational, and real implementations attack. This appendix is informational, and real implementations
SHOULD use different algorithms in order to avoid he dangers of SHOULD use different algorithms in order to avoid he dangers of
monocultural code. mono-cultural code.
There are at least two distinct cache related attack scenarios: There are at least two distinct cache related attack scenarios:
1. There are a number of nodes on a link, and someone launches a 1. There are a number of nodes on a link, and someone launches a
cache filling attack. The goal here is clearly make sure that cache filling attack. The goal here is clearly make sure that
the nodes can continue to communicate even if the attack is going the nodes can continue to communicate even if the attack is going
on. on.
2. There is already a cache filling attack going on, and a new node 2. There is already a cache filling attack going on, and a new node
arrives to the link. The goal here is to make it possible for arrives to the link. The goal here is to make it possible for
the new node to become attached to the network, inspite of the the new node to become attached to the network, inspite of the
attack. attack.
From this point of view, it is clearly better to be very selective in From this point of view, it is clearly better to be very selective in
how to throw out entries. Reducing the timestamp Delta value is very how to throw out entries. Reducing the timestamp Delta value is very
discriminative against those nodess that have a large clock discriminative against those nodes that have a large clock
difference, while an attacker can reduce its clock difference into difference, while an attacker can reduce its clock difference into
arbitrarily small. Throwing out old entries just because their clock arbitrarily small. Throwing out old entries just because their clock
difference is large seems like a bad approach. difference is large seems like a bad approach.
A reasonable idea seems to be to have a separate cache space for new A reasonable idea seems to be to have a separate cache space for new
entries and old entries, and under an attack more eagerly drop new entries and old entries, and under an attack more eagerly drop new
cache entries than old ones. One could track traffic, and only allow cache entries than old ones. One could track traffic, and only allow
those new entries that receive genuine traffic to be converted into those new entries that receive genuine traffic to be converted into
old cache entries. While such a scheme will make attacks harder, it old cache entries. While such a scheme will make attacks harder, it
will not fully prevent them. For example, an attacker could send a will not fully prevent them. For example, an attacker could send a
little traffic (i.e. a ping or TCP syn) after each NS to trick the little traffic (i.e. a ping or TCP syn) after each NS to trick the
victim into promoting its cache entry to the old cache. Hence, the victim into promoting its cache entry to the old cache. Hence, the
node may be more intelligent in keeping its cache entries, and not node may be more intelligent in keeping its cache entries, and not
just have a black/white old/new boundary. just have a black/white old/new boundary.
It also looks like a good idea to consider the sec parameter when It also looks like a good idea to consider the sec parameter when
forcing cache entries out, and let those entries with a larger sec a forcing cache entries out, and let those entries with a larger sec a
higher chance of staying in. higher chance of staying in.
Appendix D. Comparison to AH-Based Approach
This approach has the following benefits compared to the previous
Working Group document approach:
o The full implementation of the security mechanism, including
Nonces and CGAs, exists within one module. There is no need to
analyze the security of the mechanism across NDP, IPsec, and CGA
layers.
o The CGA part of the solution has been separated into its own
specification. This is possible because the CGA handling is done
in its own option. (The authorization method configuration flag
is the only thing common to the CGA and Signature options.)
o No extensions or modifications of IPsec processing are required:
SPD entries are not required to distinguish ICMP types, AH does
not need to support public keys or CGAs, and destination address
acgnostic security associations are not needed.
o It is not necessary to allocate a new multicast address to
represent the Solicited-Node multicast address for SEND nodes.
o It is not necessary to change the Neighbor Discovery behavior with
regards to the use of the unspecified address. Since all
information is available within the Neighbor Discovery messages,
unspecified source addresses can be used, still being able to
correlate the CGA property with the Target Address in a Neighbor
Solicitation during Duplicate Address Detection.
o The transition mechanisms for links with both SEND and non-SEND
nodes are significantly simpler. In particular, non-SEND nodes
will be able to receive DAD probes and other messages sent by the
SEND nodes.
o Only a single set of Neighbor Discovery messages from the router
needs to be transmitted on a link. This helps avoid extra
overhead for mobility beacons and other frequently occurring
messaging.
o Given that the asymmetric computations required in SEND are
computationally expensive, it is necessary to control the number
of these operations in order to avoid Denial-of-Service attacks.
This control is easier to arrange with "application layer"
information. For instance, a router need not verify more Router
Solicitations with an unspecified source address than it can
respond to according to the RFC 2461 rules.
o There is no need for an API to communicate certificate chains
requests and certificate chains between the IPsec and Neighbor
Discovery modules.
Also, a good implementation of SEND would not require the user to
configure it (beyond perhaps enabling it). In order to achieve
this with IPsec, a set of policy entries needs to be automatically
created upon system start.
o There is no need for the CGA parameters to be stored both in the
IPsec and Neighbor Discovery modules, where they are needed for
the construction of Authentication Headers and addresses,
respectively.
o It is not necessary to change existing BITS or BITW IPsec
implementations to support SEND and AH_RSA_Sig. There would have
been two problems associated with such changes:
* A SEND implementation in such environment could not proceed
until this modification were completed.
* Typical hardware that processes IPsec packets may not be easily
changed to process asymmetric transforms. (Of course, such
packets can be passed to the main CPU at the node, assuming
this can easily be done in the given implementation.)
o In addition, many IPsec implementations are highly optimized
because they are on the fast path for packet processing. For
example, the Linux implementation runs in the kernel interrupt
thread. Some of the SEND modifications might have required IPsec
processing to wait on a semaphore while, for example, a
certificate chain is fetched, an operation that takes place out of
band in regular IPsec processing because it is done using IKE.
While it might have been possible that the implemenation could
have been arranged so that general IPsec processing wasqn't
impacted, the resulting code would have been more complex.
The use of IPsec to protect NDP would have been possible, but the
limits and capabilities of IPsec would have to be stretched. Small
changes in the NDP protocol (or our understanding of the issues)
might have caused a situation which had no longer been easily handled
when the "application" and the security existed at different layers.
Although IPsec as defined in RFC 2402 just defines a header format,
RFC 2401 and the ensuing years of implementation have evolved a
complex interconnected set of components for IPsec which would have
required some modification to accommodate SEND.
On the other hand, IPsec is the current solution for securing NDP in
the original NDP RFCs. Even if the current IPsec can be used only in
very limited networks to secure NDP, it could have been argued that
it would have been logical to continue its use. Also, the existence
of an asymmetric transform in IPsec would have been potentially
useful in other contexts as well.
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