WDIFF

draft-ietf-send-ndopt-03.txt --> draft-ietf-send-ndopt-04.txt

Secure Neighbor Discovery Working J. Arkko Arkko, Editor
Group Ericsson
Internet-Draft J. Kempf
Expires: July 24, August 16, 2004 DoCoMo Communications Labs USA
B. Sommerfeld
Sun Microsystems
B. Zill
Microsoft
P. Nikander
Ericsson
January 24,
February 16, 2004

SEcure Neighbor Discovery (SEND)
draft-ietf-send-ndopt-03
draft-ietf-send-ndopt-04

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This Internet-Draft will expire on July 24, August 16, 2004.

Abstract

IPv6 nodes use the Neighbor Discovery Protocol (NDP) to discover
other nodes on the link, to determine each the link-layer addresses of the
other nodes on the link, to find routers, and to maintain
reachability information about the paths to active neighbors. If not

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secured, NDP is vulnerable to various attacks. This document
specifies security mechanisms for NDP. Unlike to the original NDP
specifications, these mechanisms do not make use of IPsec.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Specification of Requirements . . . . . . . . . . . . 4
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Neighbor and Router Discovery Overview . . . . . . . . . . . 7
4. Secure Neighbor Discovery Overview . . . . . . . . . . . . . 9
5. Neighbor Discovery Protocol Options . . . . . . . . . . . . 11
5.1 CGA Option . . . . . . . . . . . . . . . . . . . . . .11
5.1.1 Processing Rules for Senders . . . . . . . . . 12
5.1.2 Processing Rules for Receivers . . . . . . . . 13
5.1.3 Configuration . . . . . . . . . . . . . . . . 14
5.2 Signature Option . . . . . . . . . . . . . . . . . . .14 .15
5.2.1 Processing Rules for Senders . . . . . . . . . 16 17
5.2.2 Processing Rules for Receivers . . . . . . . . 17
5.2.3 Configuration . . . . . . . . . . . . . . . . 18
5.2.4 Performance Considerations . . . . . . . . . . 19
5.3 Timestamp and Nonce options . . . . . . . . . . . . .19 .20
5.3.1 Timestamp Option . . . . . . . . . . . . . . . 19 20
5.3.2 Nonce Option . . . . . . . . . . . . . . . . . 20 21
5.3.3 Processing rules for senders . . . . . . . . . 21
5.3.4 Processing rules for receivers . . . . . . . . 21 22
6. Authorization Delegation Discovery . . . . . . . . . . . . . 24 25
6.1 Certificate Format . . . . . . . . . . . . . . . . . .24 .25
6.1.1 Router Authorization Certificate Profile . . . 24 25
6.2 Certificate Transport . . . . . . . . . . . . . . . .27 .28
6.2.1 Delegation Chain Solicitation Message Format . 27 28
6.2.2 Delegation Chain Advertisement Message Format 29 30
6.2.3 Trust Anchor Option . . . . . . . . . . . . . 31 32
6.2.4 Certificate Option . . . . . . . . . . . . . . 32 34
6.2.5 Processing Rules for Routers . . . . . . . . . 33 35
6.2.6 Processing Rules for Hosts . . . . . . . . . . 34 36
7. Addressing . . . . . . . . . . . . . . . . . . . . . . . . . 37 38
7.1 CGA Addresses CGAs . . . . . . . . . . . . . . . . . . . . . . .37 . . .38
7.2 Redirect Addresses . . . . . . . . . . . . . . . . . .37 .38
7.3 Advertised Prefixes . . . . . . . . . . . . . . . . .37 .38
7.4 Limitations . . . . . . . . . . . . . . . . . . . . .38 .39
8. Transition Issues . . . . . . . . . . . . . . . . . . . . . 39 41
9. Security Considerations . . . . . . . . . . . . . . . . . . 41 43
9.1 Threats to the Local Link Not Covered by SEND . . . .41 .43
9.2 How SEND Counters Threats to NDP . . . . . . . . . . .41 .43
9.2.1 Neighbor Solicitation/Advertisement Spoofing . 42 44
9.2.2 Neighbor Unreachability Detection Failure . . 42 44
9.2.3 Duplicate Address Detection DoS Attack . . . . 42 44

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9.2.4 Router Solicitation and Advertisement Attacks 43 45
9.2.5 Replay Attacks . . . . . . . . . . . . . . . . 43 45
9.2.6 Neighbor Discovery DoS Attack . . . . . . . . 44 46
9.3 Attacks against SEND Itself . . . . . . . . . . . . .44 .46
10. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 46 48
11. Protocol Variables . . . . . . . . . . . . . . . . . . . . . 49
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 47 50
Normative References . . . . . . . . . . . . . . . . . . . . 48 51
Informative References . . . . . . . . . . . . . . . . . . . 50 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 51 53
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 52 55
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 53 56
C. Cache Management . . . . . . . . . . . . . . . . . . . . . . 54 57
Intellectual Property and Copyright Statements . . . . . . . 55 58

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1. Introduction

IPv6 defines the Neighbor Discovery Protocol (NDP) in RFCs 2461 [7]
and 2462 [8]. Nodes on the same link use NDP to discover each
other's presence, to determine each other's link-layer addresses, to
find routers, and to maintain reachability information about the
paths to active neighbors. NDP is used both by hosts and routers.
Its functions include Neighbor Discovery (ND), Router Discovery (RD),
Address Autoconfiguration, Address Resolution, Neighbor
Unreachability Detection (NUD), Duplicate Address Detection (DAD),
and Redirection.

Original

The original NDP specifications called for the use of IPsec for
protecting the to
protect NDP messages. However, the RFCs do not give detailed
instructions for using IPsec to secure NDP. It turns out that in for this. In this particular
application, IPsec can only be used with a manual configuration of
security associations, due to chicken-and-egg bootstrapping problems in using IKE [20, 15].
[21, 16]. Furthermore, the number of such manually configured
security associations needed for protecting NDP can be very large [21],
[22], making that approach impractical for most purposes.

This document is organized as follows. Section 2 and Section 3
define some terminology and present a brief review of NDP,
respectively. Section 4 describes the overall approach to securing
NDP. This approach involves the use of new NDP options to carry
public-key based signatures. A zero-configuration mechanism is used
for showing address ownership on individual nodes; routers are
certified by a trust anchor [10]. The formats, procedures, and
cryptographic mechanisms for the zero-configuration mechanism are
described in a related specification
[12]. [13].

The required new NDP options are discussed in Section 5. Section 6
describes the mechanism for distributing certificate chains to
establish an authorization delegation chain to a common trust anchor.

Finally, Section 8 discusses the co-existence of secure and
non-secure NDP on the same link and Section 9 discusses security
considerations for Secure Neighbor Discovery. Discovery (SEND).

1.1 Specification of Requirements

In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. The key
words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", and
"MAY" in this document are to be interpreted as described in [2].

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2. Terms

Authorization Delegation Discovery (ADD)

A process through which SEND nodes can acquire a certificate chain
from a peer node to a trust anchor.

Cryptographically Generated Address (CGA)

A technique [12] where the [13] whereby an IPv6 address of a node is
cryptographically generated using a one-way hash function from the
node's public key and some other parameters.

Duplicate Address Detection (DAD)

A mechanism that which assures that two IPv6 nodes on the same link are
not using the same addresses.

Internet Control Message Protocol version 6 (ICMPv6)

The IPv6 control signaling protocol. Neighbor Discovery Protocol
is a part of ICMPv6. address.

Neighbor Discovery Protocol (NDP)

The IPv6 Neighbor Discovery Protocol [7, 8].

Neighbor Discovery Protocol is a part of ICMPv6 [9].

Neighbor Discovery (ND)

The Neighbor Discovery function of the Neighbor Discovery Protocol
(NDP). NDP contains also other functions but besides ND.

Neighbor Unreachability Detection (NUD)

This

A mechanism is used for tracking the reachability of neighbors.

Nonce

An unpredictable random or pseudorandom number generated by a node
and used exactly once. In SEND, nonces are used to ensure assure that a
particular advertisement is linked to the solicitation that
triggered it.

Router Authorization Certificate

An X.509v3 [10] PKC public key certificate using the profile specified
in Section 6.1.1.

SEND node

An IPv6 node that implements this specification.

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SEND node

An IPv6 node that implements this specification.

non-SEND

Non-SEND node

An IPv6 node that does not implement this specification but uses
the legacy
only RFC 2461 and RFC 2462 mechanisms. without security.

Router Discovery (RD)

The

Router Discovery function allows the hosts to discover what routers exist
on the link, and what prefixes are available. Router Discovery is
a part of the Neighbor Discovery Protocol.

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3. Neighbor and Router Discovery Overview

The Neighbor Discovery Protocol has several functions. Many of these
functions are overloaded on a few central message types, such as the
ICMPv6 Neighbor Advertisement message. In this section we review
some of these tasks and their effects in order to understand better
how the messages should be treated. This section is not normative,
and if this section and the original Neighbor Discovery RFCs are in
conflict, the original RFCs take precedence.

The main functions of NDP are the following.

o The Router Discovery function allows IPv6 hosts to discover the
local routers on an attached link. Router Discovery is described
in Section 6 of RFC 2461 [7]. The main purpose of Router
Discovery is to find neighboring routers that are willing to
forward packets on behalf of hosts. Prefix discovery involves
determining which destinations are directly on a link; this
information is necessary in order to know whether a packet should
be sent to a router or directly to the destination node directly. node.

o The Redirect function is used for automatically redirecting a host
to a better first-hop router, or to inform hosts that a
destination is in fact a neighbor (i.e., on-link). Redirect is
specified in Section 8 of RFC 2461 [7].

o Address Autoconfiguration is used for automatically assigning
addresses to a host [8]. This allows hosts to operate without
explicit configuration related to IP connectivity. The default
autoconfiguration mechanism is stateless. To create IP addresses,
the
hosts use any prefix information delivered to them during Router
Discovery, and then test the newly formed addresses for
uniqueness. A stateful mechanism, DHCPv6 [23], [20], provides
additional autoconfiguration features.

o Duplicate Address Detection (DAD) is used for preventing address
collisions [8], for instance during Address Autoconfiguration. A
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
using the same address. Since the rules forbid the use of an
address until it has been found unique, no higher layer traffic is
possible until this procedure has been completed. Thus,
preventing attacks against DAD can help ensure the availability of
communications for the node in question.

o The Address Resolution function resolves allows a node on the link to
resolve another node's IPv6 address to the corresponding
link-layer address for nodes on the link. address. Address Resolution is defined in Section 7.2 of RFC 2461 [7], and

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of RFC 2461 [7], and it is used for hosts and routers alike.
Again, no higher level traffic can proceed until the sender knows
the hardware link layer address of the destination node or the next hop
router. Note the source link layer address on link layer frames
is not checked against the information learned through 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
from layer to layer.

o Neighbor Unreachability Detection (NUD) is used for tracking the
reachability of neighboring nodes, both hosts and routers. NUD is
defined in Section 7.3 of RFC 2461 [7]. NUD is
security-sensitive, because an attacker could falsely claim that
reachability exists when it in fact does not.

The NDP messages follow the ICMPv6 message format. All NDP functions
are realized using the Router Solicitation (RS), Router Advertisement
(RA), Neighbor Solicitation (NS), Neighbor Advertisement (NA), and
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.

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4. Secure Neighbor Discovery Overview

To secure the various functions, functions in NDP, a set of new Neighbor
Discovery options is introduced. They are used in to protect NDP
messages. This specification introduces these options, an
authorization delegation discovery process, an address ownership
proof mechanism, and requirements for the use of these components in
NDP.

The components of the solution specified in this document are as
follows:

o Certificate chains, anchored on trusted parties, are expected to
certify the authority of routers. A host and a router must have
at least one common trust anchor before the host can adopt the
router as its default router. Delegation Chain Solicitation and
Advertisement messages are used to discover a certificate chain to
the trust anchor without requiring the actual Router Discovery
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 the authorization delegation discovery
process.

o Cryptographically Generated Addresses are used to assure that the
sender of a Neighbor or Router Advertisement Discovery message is the "owner" of the
claimed address. A public-private key pair needs to be is generated by all
nodes before they can claim an address. A new NDP option, the CGA
option, is used to carry the public key and associated parameters.

This specification also allows one to use non-CGA addresses and a node to use non-CGAs with
certificates to authorize their use. However, the details of such
use have been left for future work. are beyond the scope of this specification.

o A new NDP option, the Signature option, is used to protect all
messages relating to Neighbor and Router discovery.

Public key signatures are used to protect the integrity of the messages and to
authenticate the identity of their sender. The authority of a
public key is established either with the authorization delegation
process, using certificates, or through the address ownership
proof mechanism, using CGAs, or both, depending on configuration
and the type of the message protected.

o In order to prevent replay attacks, two new Neighbor Discovery
options, Timestamp and Nonce, are used. introduced. Given that Neighbor
and Router Discovery messages are in some cases sent to multicast
addresses, the Timestamp option offers replay protection without
any previously established state or sequence numbers. When the
messages are used in solicitation - advertisement pairs, they are

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messages are used in solicitation - advertisement pairs, they are
protected using the Nonce option.

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5. Neighbor Discovery Protocol Options

The options described in this section MUST be supported by all SEND
nodes.

5.1 CGA Option

The CGA option allows the verification of the sender's CGA. The
format of the CGA option is described as follows.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Collision Cnt | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Modifier |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Key Information .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The meaning of the fields is described as follows.

Type

TBD <To be assigned by IANA> IANA for CGA. CGA>.

Length

The length of the option, option (including the Type, Length, Collision
Cnt, Reserved, Modifier, Key Information, and Padding fields) in
units of 8 octets.

Collision Cnt

An 8-bit collision count, which can get values be 0, 1 and or 2. Its semantics
are defined in [12]. [13].

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Reserved

An 8-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.

Modifier

A random 128-bit number used in CGA generation. Its semantics are
defined in [12]. [13].

Key Information

A variable length field containing the public key of the sender,
represented as an ASN.1 type SubjectPublicKeyInfo [10], encoded as
described in Section 4 of [12]. [13].

This specification requires that if both the CGA option and the
Signature option are present, then the publicKey field in the
former CGA
option MUST be the public key referred by the Key Hash field in
the latter Signature option. Packets received with two different keys
MUST be silently discarded. Note that a future extension may
provide a mechanism which allows the owner of an address and the
signer to be different parties.

The length of the Key Information field is determined by the ASN.1
encoding.

Padding

A variable length field making the option length a multiple of 8.
It begins 8,
beginning after the ASN.1 encoding of the previous field has ends, and continues
continuing to the end of the option, as specified by the Length
field.

5.1.1 Processing Rules for Senders

The CGA option MUST be present in all Neighbor Solicitation and
Advertisement messages, and MUST be present in Router Solicitation
messages not unless they are 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
message as follows.

The Modifier, Collision Cnt, and Key Information fields in the CGA
option are filled in according to the rules presented above and in

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[12].

[13]. The used public key in the Key Information field is taken from configuration; the
node's configuration used to generate the CGA; typically from a data
structure associated with the source address. The address MUST be
constructed as specified in Section 4 of [12]. [13]. Depending on the type
of the message, this address appears in different places:

Redirect

The address MUST be the source address of the message.

Neighbor Solicitation

The address MUST be the Target Address for solicitations sent for
the purpose of
Duplicate Address Detection, and the source address of the message
otherwise.

Neighbor Advertisement

The address MUST be the source address of the message.

Router Solicitation

The address MUST be the source address of the message. Note that
the CGA option is not used when the source address is the
unspecified address.

Router Advertisement

The address MUST be the source address of the message.

5.1.2 Processing Rules for Receivers

Neighbor Solicitation and Advertisement messages without the CGA
option MUST be silently discarded. treated as insecure, i.e., processed in the same way
as NDP messages sent by a non-SEND node. The processing of insecure
messages is specified in Section 8. Note that SEND nodes that do not
attempt to interoperate with non-SEND nodes MAY simply discard the
insecure messages.

Router Solicitation messages without the CGA option MUST be silently discarded, also
treated as insecure, unless the source address of the message is the
unspecified address.

A message containing a CGA option MUST be checked as follows:

If the interface has been configured to use CGA, the receiving
node MUST verify the source address of the packet using the

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algorithm described in Section 5 of [12]. [13]. The inputs for to the
algorithm are the claimed address, as defined in the previous
section, and the concatenation from left to right of the following
data: the contents of the Collision Cnt, Modifier, and 8-octet Modifier field, the
Key Information fields, 8-octet
subnet-prefix part of the claimed address in address, the packet (as
discussed in content of the previous section),
1-octet Collision Cnt field, and contents of the minimum acceptable Sec
value. variable-length
Key Information Field.

If the CGA verification is successful, the recipient proceeds with
the cryptographically more time consuming check of

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However, even if the CGA verification succeeds, no claims about
the validity of the use can be made, until the signature has been
checked.

Note that a receiver which that does not support CGA or has not specified
its use for a given interface can still verify packets using trust
anchors, even if a CGA had been is used on a packet. In such a case, the CGA
property of the address is simply left unverified.

5.1.3 Configuration

All nodes that support the verification of the CGA option MUST record
the following configuration information:

minbits

The minimum acceptable key length for the public keys used in the
generation of the CGA address. CGAs. The default SHOULD be 1024 bits.
Implementations MAY also set an upper limit in order to limit the
amount of computation they need to perform when verifying packets
that use these security associations. The upper limit SHOULD be
at least 2048 bits. Any implementation should follow prudent
cryptographic practice in determining the appropriate key lengths.

minSec

The minimum acceptable Sec value, if CGA verification is required
(see Section 2 in [12]). required.
This parameter is intended to facilitate future extensions and
experimental work. Currently, the minSec value SHOULD always be
set to zero.

See Section 2 in [13].

All nodes that support the sending of the CGA option MUST record the
following configuration information:

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CGA parameters

Any information required to construct CGAs, including the used Sec
and Modifier values, and the CGA address itself.

5.2 Signature Option

The Signature option allows public-key based signatures to be
attached to NDP messages. Both Configured trust anchor authentication and CGAs
can be used. anchors, CGAs, or both
are supported as the trusted root. The format of the Signature
option is described in the
following:

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Pad Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Key Hash |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Digital Signature .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The meaning of the fields is described below:

Type

TBD <To be assigned by IANA> IANA for Signature. Signature>.

Length

The length of the option, option (including the Type, Length, Pad Length,
Reserved, Key Hash, Digital Signature, and Padding fields) in
units of 8 octets.

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Pad Length

An 8-bit integer field, giving the length of the Pad field in
units of an octet.

Reserved

An an 8-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.

Key Hash

A 128-bit field contains containing the most significant (leftmost)
128-bits of a SHA1 SHA-1 hash of the public key used for the constructing
the

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in the Key Information field in of the CGA option. Its purpose is to
associate the signature to a particular key known by the receiver.
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.

Digital Signature

A variable length field contains the signature containing a PKCS#1 signature, constructed
using the sender's private key, over the the following sequence of
octets:

1. The 128-bit CGA Message Type Tag [12] tag [13] value for SEND, 0x086F
CA5E 10B2 00C9 9C8C E001 6427 7C08 (generated randomly). 7C08. (The tag value has been
generated randomly by the editor of this specification.).

2. The 128-bit Source Address field from the IP header.

3. The 128-bit Destination Address field from the IP header.

4. The 32-bit ICMP header.

5. The NDP message header.

6. All NDP options preceding the Signature option.

The signature is constructed using the RSA algorithm and MUST be
encoded as private key encryption in PKCS#1 format [13]. The
signature value is computed with the RSASSA-PKCS1-v1_5
algorithm and SHA-1 hash as defined in [13]. [14].

This field starts after the Key Hash field. The length of the
Digital Signature field is determined by the length of the
Signature option minus the length of the other fields (including
the variable length Pad field).

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Padding

This variable length field contains padding, as many bytes as is
given by the Pad Length Field. field.

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
the message as follows:

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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 For the purpose of constructing a signature, the following data
items are concatenated:

* The 128-bit CGA Type Tag.

* The source address of the message.

* The destination address of the message.

* The contents of the message, starting from the ICMPv6 header,
up to but excluding the Signature option.

o The message, in the form defined above, is signed using the
configured private key, and the resulting PKCS#1 signature is put
to the Digital Signature field.

5.2.2 Processing Rules for Receivers

Neighbor Solicitation, Neighbor Advertisement, Router Advertisement,
and Redirect messages without the Signature option MUST be silently
discarded. treated as
insecure, i.e., processed in the same way as NDP messages sent by a
non-SEND node. See Section 8.

Router Solicitation messages without the Signature option MUST be silently discarded,
also treated as insecure, unless the source address of the message is
the unspecified address.

A message containing a Signature

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A message containing a Signature option MUST be checked as follows:

o The Signature option receiver MUST appear as ignore any options the last come after the first
Signature option.

o The Key Hash field MUST indicate the use of a known public key,
either one learned from a preceding CGA option, option in the same
message, or one known by other means.

o The Digital Signature field MUST have correct encoding, and not
exceed the length of the Signature option. option minus the Padding.

o The Digital Signature verification MUST show that the signature
has been calculated as specified in the previous section.

o If the use of a trust anchor has been configured, a valid
authorization delegation chain MUST be known between the
receiver's trust anchor and the sender's public key.

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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
anchor.

Messages that do not pass all the above tests MUST be silently
discarded. The receiver MAY also otherwise silently discard packets also otherwise, packets,
e.g., as a response to an apparent CPU exhausting DoS attack.

5.2.3 Configuration

All nodes that support the reception of the Signature options MUST
record be
configured with the following configuration information for each separate NDP
message type:

authorization method

This parameter determines the method through which the authority
of the sender is determined. It can have four values:

trust anchor

The authority of the sender is verified as described in Section
6.1. The sender may claim additional authorization through the
use of CGAs, but that is neither required nor verified.

CGA

The CGA property of the sender's address is verified as
described in [12]. [13]. The sender may claim additional authority

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through a trust anchor, but that is neither required nor
verified.

trust anchor and CGA

Both the trust anchor and the CGA verification is required.

trust anchor or CGA

Either the trust anchor or the CGA verification is required.

anchor

The public keys and names of the allowed trust anchor(s), if the
authorization method is not set to CGA.

All nodes that support the sending of Signature options MUST record
the following configuration information:

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keypair

A public-private key pair. If authorization delegation is in use,
there must exist a delegation chain from a trust anchor to this
key pair.

CGA flag

A flag that indicates whether CGA is used or is not used. not. This flag may
be per interface or per node. (Note that in future extensions of
the SEND protocol, this flag may be per subnet-prefix.)

5.2.4 Performance Considerations

The construction and verification of this option is computationally
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 explained 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.

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Signatures can be precomputed for unsolicited (multicast) Neighbor
and Router Advertisements, 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 solicited advertisements.

5.3 Timestamp and Nonce options

5.3.1 Timestamp Option

The purpose of the Timestamp option is to ensure assure that unsolicited
advertisements and redirects have not been replayed. The format of
this option is described in the following:

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where the fields are as follows:

Type

TBD <To be assigned by IANA> IANA for Timestamp. Timestamp>.

Length

The length of the option, option (including the Type, Length, Reserved,
and Timestamp fields) in units of 8 octets, i.e., 2.

Reserved

A 48-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.

Timestamp

A 64-bit unsigned integer field containing a timestamp. The value
indicates the number of seconds since January 1,, 1, 1970 00:00 UTC,
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

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remaining 16 bits indicate the number of 1/64K fractions of a
second.

5.3.2 Nonce Option

The purpose of the Nonce option is to ensure assure that an advertisement is
a fresh response to a solicitation sent earlier by the receiving same node. The
format of this option is described in the following:

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where the fields are as follows:

Type

TBD <To be assigned by IANA> IANA for Nonce. Nonce>.

Length

The length of the option, option (including the Type, Length, and Nonce
fields) in units of 8 octets.

Nonce

A field containing a random number selected by the sender of the
solicitation message. The length of the random number MUST be at
least 6 bytes. The length of the random number MUST be selected
so that the length of the nonce option is a multiple of 8 octets.

5.3.3 Processing rules for senders

All solicitation messages MUST include a Nonce. All solicited-for
advertisements MUST include a Nonce, copying the nonce value from the
received solicitation. When sending a
solicitation, the sender MUST store the nonce internally so that it
can recognize any replies containing that particular nonce.

All solicitation, advertisement, and redirect messages MUST solicited advertisements MUST include a Nonce, copied from the
received solicitation. Note that routers may decide to send a
multicast advertisement to all nodes instead of a response to a
specific host. In such case the router MAY still include the nonce

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value for the host that triggered the multicast advertisement.

All solicitation, advertisement, and redirect messages MUST include a
Timestamp. Senders SHOULD set the Timestamp field to the current
time, according to their real time clock.

If a message has both Nonce and Timestamp options, the Nonce option
SHOULD precede the Timestamp option in order. the message.

5.3.4 Processing rules for receivers

The processing of the Nonce and Timestamp options depends on whether
a packet is a solicited-for advertisement or not. solicited advertisement. A system may implement the
distinction in various means. ways. Section 5.3.4.1 defines

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rules for solicited-for solicited advertisements. Section 5.3.4.2 defines the
processing rules for all other messages.

In addition, the following rules apply in any case: all cases:

o Messages received with the Signature option but without the
Timestamp option MUST be silently discarded.

o Solicitation messages received with the Signature option but
without the Nonce option MUST be silently discarded.

o Advertisements sent to a unicast destination address with the
Signature option but without a Nonce option MUST be silently
discarded.

o An implementation may MAY utilize some mechanism such as a timestamp
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 attack is in progress, it is possible that the cache
holding the most recent timestamp per sender becomes full. In
this case the node MUST remove some entries from the cache or
refuse some new requested entries. The specific policy as to
which entries are preferred over the others is left as an
implementation decision. However, typical policies may prefer
existing entries over new ones, CGAs with a large Sec value over
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.

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5.3.4.1 Processing solicited-for solicited advertisements

The receiver MUST verify that it has recently sent a matching
solicitation, and that the received advertisement contains a copy of
the Nonce sent in the solicitation.

If the message contains a Nonce option, but the Nonce value is not
recognized, the message MUST be silently discarded.

Otherwise, if the message does not contain a Nonce option, it MAY be
considered as a non-solicited-for an unsolicited advertisement, and processed according
to Section 5.3.4.2.

If the message is accepted, the receiver SHOULD store the receive
time of the message and the time stamp time in the message, as
specified in Section 5.3.4.2

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5.3.4.2 Processing all other messages

Receivers SHOULD be configured with an allowed timestamp Delta value,
a "fuzz factor" for comparisons, and an allowed clock drift
parameter. The recommended default value for the allowed Delta is
3,600 seconds (1 hour),
TIMESTAMP_DELTA, for fuzz factor 1 second, TIMESTAMP_FUZZ, and for clock drift
1% (0.01).
TIMESTAMP_DRIFT (see Section 11.

To facilitate timestamp checking, each node SHOULD store the
following information per for each peer:

o The receive time of the last received, received and accepted SEND message.
This is called RDlast.

o The time stamp in the last received, received and accepted SEND message.
This is called TSlast.

An accepted SEND message is any successfully verified Neighbor
Solicitation, Neighbor Advertisement, Router Solicitation, Router
Advertisement, or Redirect message from the given peer. It is
required that the Signature option has been used in such a message
before it can update the above variables.

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
stored in the cache, the received timestamp, TSnew, is checked and
the packet is accepted if the timestamp is recent enough with
respect to the reception time of the packet, RDnew:

-Delta < (RDnew - TSnew) < +Delta

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The RDnew and TSnew values SHOULD be stored into the cache as
RDlast and TSlast.

o If the timestamp is NOT within the boundaries but the message is a
Neighbor Solicitation message that which should be responded to answered by the
receiver, the receiver MAY respond to the message. However, if it
does respond to the message, it MUST NOT create a neighbor cache Neighbor Cache
entry. This allows nodes that have large difference differences in their
clocks to still communicate with each other, by exchanging NS/NA
pairs.

o When a message is received from a known peer, i.e., one that
already has an entry in the cache, the time stamp is checked
against the previously received SEND message:

TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz

If this inequality does not hold, the receiver SHOULD silently
discard the message. On the other hand, if the inequality holds,
the receiver SHOULD process the message.

Moreover, if the above inequality holds and TSnew < > TSlast, which is possible if packets arrive rapidly the
receiver SHOULD update RDlast and
out of order, TSlast MUST NOT be updated, i.e., TSlast. Otherwise, the stored TSlast
for a given node receiver
MUST NOT ever decrease. Otherwise TSlast SHOULD
be updated. Independent on whether TSlast is updated or not, update update RDlast is updated in any case. or TSlast.

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6. Authorization Delegation Discovery

Several protocols (NDP included) allow

NDP allows a node to automatically configure itself based on
information it learns learned shortly after connecting to a new link. It is
particularly easy to configure "rogue" routers on an unsecured link,
and it is particularly difficult for a node to distinguish between
valid and invalid sources of router information, when because the node
needs this information before being able to communicate with nodes
outside of the link.

Since the newly-connected node cannot communicate off-link, it cannot
be responsible for searching information to help validating validate the
router(s); however, given a chain of appropriately signed
certificates, it can check someone else's search results and conclude
that a particular message comes from an authorized source. In the
typical case, a router, which is router already connected to beyond the link, can (if
necessary) communicate with off-link nodes and construct such a
certificate chain.

The Secure Neighbor Discovery Protocol mandates a certificate format
and introduces two new ICMPv6 messages that are used between hosts
and routers to allow the host to learn a certificate chain with the
assistance of the router.

6.1 Certificate Format

The certificate chain of a router terminates in a Router
Authorization Certificate that authorizes a specific IPv6 node to act
as a router. Because authorization chains are not a common practice
in the Internet at the time this specification is being was written, the chain
MUST consist of standard Public Key Certificates (PKC, in the sense
of [18]). [19]). The certificate chain MUST start from the identity 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 trust
anchor. Note that there MAY be multiple certificates issued by a
single trust anchor.

6.1.1 Router Authorization Certificate Profile

Router Authorization Certificates be are X.509v3 certificates, as
defined in RFC 3280 [10], and MUST contain at least one instance of
the X.509 extension for IP addresses, as defined in [11]. [12]. The parent
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
ISP) that configured the original IP address space block for the
router in question, or delegated the right to do so for someone. so. The
certificates for the intermediate delegating authorities MUST contain
X.509 IP address extension(s) for subdelegations. The router's

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certificate is signed by the delegating authority for the prefixes
the router is authorized to to advertise.

The X.509 IP address extension MUST contain at least one
addressesOrRanges element. This element MUST contain an
addressPrefix element with containing an IPv6 address prefix for a prefix
the router or the intermediate entity is authorized to route. If the
entity is allowed to route any prefix, the used IPv6 address prefix
is the null prefix, 0/0. ::/0. The addressFamily element of the
containing IPAddrBlocks sequence element MUST contain the IPv6
Address Family Identifier (0002), as specified in [11] [12] for IPv6
prefixes. Instead of an addressPrefix element, the addressesOrRange
element MAY contain an addressRange element for a range of prefixes,
if more than one prefix is authorized. The X.509 IP address
extension MAY contain additional IPv6 prefixes, expressed either as
an addressPrefix or an addressRange.

A SEND node receiving a Router Authorization Certificate MUST first
check whether the certificate's signature was generated by the
delegating authority. Then the client MUST check whether all the
addressPrefix or addressRange entries in the router's certificate are
contained within the address ranges in the delegating authority's
certificate, and whether the addressPrefix entries match any
addressPrefix entries in the delegating authority's certificate. If
an addressPrefix or addressRange is not contained within the
delegating authority's prefixes or ranges, the client MAY attempt to
take an intersection of the ranges/prefixes, and use that
intersection. If the addressPrefix in the certificate is the null
prefix, 0/0, ::/0, such an intersection SHOULD be used. (In that case the
intersection is the parent prefix or range.) If the resulting
intersection is empty, the client MUST NOT accept the certificate.

The above check SHOULD be done for all certificates in the chain. If
any of the checks fail, the client MUST NOT accept the certificate.
The client also needs to perform validation of advertised prefixes as
discussed in Section 7.3.

Care should be taken if the certificates used in SEND are re-used to
provide authorization in other circumstances, for example with
routing gateway protocols. It is necessary to ensure that the authorization
information is appropriate for all applications. SEND certificates
may authorize a larger set of prefixes than the router is really
authorized to advertise on a given interface. For instance, SEND
allows the use of the null prefix. This prefix might cause
verification or routing problems in other applications. It is
RECOMMENDED that SEND certificates containing the null prefix are
only used for SEND.

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Since it is possible that some PKC public key certificates used with SEND
do not immediately contain the X.509 IP address extension element, an
implementation MAY contain facilities that allow the prefix and range
checks to be relaxed. However, any such configuration options SHOULD
be off by default. That is, the system SHOULD have a default
configuration that requires rigorous prefix and range checks.

The following is an example of a certificate chain. Suppose that
ispgroup.com
isp_group_example.net is the trust anchor. The host has this certificate for
it:
certificate:

Certificate 1:
Issuer: isp_group.com isp_group_example.net
Validity: Jan 1, 2004 through Dec 31, 2004
Subject: isp_group.com isp_group_example.net
Extensions:
IP address delegation extension:
Prefixes: P1, ..., Pk
... possibly other extensions ...
... other certificate parameters ...

When the host attaches then to a linked link served by
router_x.isp_foo.com,
router_x.isp_foo_example.net, it receives the following certificate
chain:

Certificate 2:
Issuer: isp_group.com isp_group_example.net
Validity: Jan 1, 2004 through Dec 31, 2004
Subject: isp_foo.com isp_foo_example.net
Extensions:
IP address delegation extension:
Prefixes: Q1, ..., Qk
... possibly other extensions ...
... other certificate parameters ...

Certificate 3:
Issuer: isp_foo.com isp_foo_example.net
Validity: Jan 1, 2004 through Dec 31, 2004
Subject: router_x.isp_foo.com router_x.isp_foo_example.net
Extensions:
IP address delegation extension:
Prefixes R1, ..., Rk
... possibly other extensions ...
... other certificate parameters ...

When processing the three certificates, the usual RFC 3280 [10]
certificate path validation is performed, for instance by performed. Note, however, that at the
time a node is checking
for revoked certificates. certificates received in a DCA from a router,

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it typically does not have a connection to the Internet yet, and so
it is not possible to perform an on-line Certificate Revocation List
(CRL) check if such a check is necessary. Until such a check is
performed, acceptance of the certificate MUST be considered
provisional, and the node MUST perform a check as soon as it has
established a connection with the Internet through the router. If
the router has been compromised, it could interfere with the CRL
check. Should performance of the CRL check be disrupted or should
the check fail, the node SHOULD immediately stop using the router as
a default and use another router on the link instead.

In addition, the IP addresses in the delegation extension must be subsumed by a
subset of the IP addresses in the

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issuer's certificate. So in this example, R1, ..., Rs must be subsumed by a
subset of Q1,...,Qr, and Q1,...,Qr must be subsumed by a subset of P1,...,Pk. If
the certificate chain is valid, then router_foo.isp_foo_example.com
is authorized to route the prefixes R1,...,Rs.

6.2 Certificate Transport

The Delegation Chain Solicitation (DCS) message is sent by a host
when it wishes to request a certificate chain between a router and
the one of the host's trust anchors. The Delegation Chain
Advertisement (DCA) message is sent as an answer in reply to the DCS message.
These messages are separate from the rest of Neighbor and Router
Discovery, in order to reduce the effect of the potentially
voluminous certificate chain information on other messages.

The Authorization Delegation Discovery (ADD) process does not exclude
other forms of discovering certificate chains. For instance, during
fast movements mobile nodes may learn information - including the
certificate chains - of the next router from a previous router.

Where hosts themselves are certified by router, or
nodes may be preconfigured with certificate chains from roaming
partners.

Where hosts themselves are certified by a trust anchor, these
messages MAY also optionally be used between hosts to acquire the
peer's certificate chain. However, the details of such usage are
left for future
beyond the scope of this specification.

6.2.1 Delegation Chain Solicitation Message Format

Hosts send Delegation Chain Solicitations in order to prompt routers
to generate Delegation Chain Advertisements.

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IP Fields:

Source Address

A link-local unicast address assigned to the sending interface,
or the unspecified address if no address is assigned to the
sending interface.

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Destination Address

Typically the All-Routers multicast address, the Solicited-Node
multicast address, or the address of the host's default router.

Hop Limit

255

ICMP Fields:

Type

TBD <To be assigned by IANA> IANA for Delegation Chain Solicitation. Solicitation>.

Code

Checksum

The ICMP checksum [9].

Identifier

A 16-bit unsigned integer field, acting as an identifier to
help matching advertisements to solicitations. The Identifier
field MUST NOT be zero, and its value SHOULD be randomly
generated. (This This randomness does not need to be
cryptographically hard, though. Its since its purpose is only to avoid
collisions.)

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collisions.

Reserved

An unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver.

Valid Options:

Trust Anchor

One or more trust anchors that the client is willing to accept.
The first (or only) Trust Anchor option MUST contain a DER
Encoded X.501 Name; see Section 6.2.3. If there is more than
one Trust Anchor option, the options past the first one may
contain any types type of Trust Anchors.

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Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize
and continue processing the message. All included options MUST
have a length that is greater than zero.

ICMP length (derived from the IP length) MUST be 8 or more octets.

6.2.2 Delegation Chain Advertisement Message Format

Routers send out Delegation Chain Advertisement messages in response
to a Delegation Chain Solicitation.

IP Fields:

Source Address

A link-local unicast address assigned to the interface from
which this message is sent. Note that routers may use multiple

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addresses, and therefore this address is not sufficient for the
unique identification of routers.

Destination Address

Either the Solicited-Node multicast address of the receiver or
the link-scoped All-Nodes multicast address.

Hop Limit

255

ICMP Fields:

Type

TBD <To be assigned by IANA> IANA for Delegation Chain

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Advertisement.
Advertisement>.

Code

Checksum

The ICMP checksum [9].

Identifier

A 16-bit unsigned integer field, acting as an identifier to
help matching advertisements to solicitations. The Identifier
field MUST be zero for advertisements sent to the All-Nodes
multicast address and MUST NOT be zero for others.

Component

A 16-bit unsigned integer field, used for informing the
receiver which certificate is being sent, and how many are
still left to be sent in the whole chain.

A single advertisement MUST be broken into separately sent
components if there is more than one Certificate option, in
order to avoid excessive fragmentation at the IP layer. Unlike
the fragmentation at the IP layer, individual components of an
advertisement may be stored and used before all the components
have arrived; this makes them slightly more reliable and less
prone to Denial-of-Service attacks.

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The first message in a N-component advertisement has the
Component field set to N-1, the second set to N-2, and so on.
Zero indicates that there are no more components coming in this
advertisement.

The components MUST be ordered so that the certificate after
the trust anchor end of
the chain is the one sent first. Each certificate sent
after
it the first can be verified with the previously sent
certificates. The certificate of the sender comes last.

Reserved

An unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver.

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Valid Options:

Certificate

One certificate is provided in each Certificate option, to
establish a (part of a) certificate chain to a trust anchor.

The certificate of the trust anchor itself SHOULD NOT be
included.

Trust Anchor

Zero or more Trust Anchor options may be included to help
receivers decide which advertisements are useful for them. If
present, these options MUST appear in the first component of a
multi-component advertisement.

ICMP length (derived from the IP length) MUST be 8 or more octets.

6.2.3 Trust Anchor Option

The format of the Trust Anchor option is described in the following:

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Name Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where the fields are as follows:

Type

TBD <To be assigned by IANA> IANA for Trust Anchor. Anchor>.

Length

The length of the option, (including the Type, Length, Name Type,
Name
Pad Length, and Name fields,) fields) in units of 8 octets.

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Name Type

The type of the name included in the Name field. This
specification defines only one two legal value values for this field:

1 DER Encoded X.501 Name
2 FQDN

Pad Length

The number of padding octets beyond the end of the Name field but
within the length specified by the Length field. Padding octets
MUST be set to zero by senders and ignored by receivers.

Name

When the Name Type field is set to 1, the Name field contains a
DER encoded X.501 certificate Name, represented and encoded
exactly as in the matching X.509v3 trust anchor certificate.

When the Name Type field is set to 2, the Name field contains a
Fully Qualified Domain Name of the trust anchor, for example,
"trustanchor.example.com". The name is stored as a string, in the
"preferred name syntax" DNS format, as specified in RFC 1034 [1]
Section 3.5. Additionally, the restrictions discussed in RFC 3280
[10] Section 4.2.1.7 apply.

In the FQDN case the Name field is an "IDN-unaware domain name
slot" as defined in [11]. That is, it can contain only ASCII
characters. An implementation MAY support internationalized
domain names (IDNs) using the ToASCII operation; see [11] for more

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information.

All systems MUST implement support the DER Encoded X.501 Name.
Implementations MAY support the FQDN name type.

6.2.4 Certificate Option

The format of the certificate option is described in the following:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Cert Type | Pad Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Certificate ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where the fields are as follows:

Type

TBD <To be assigned by IANA> IANA for Certificate.

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Length

The length of the option, (including the Type, Length, Cert Type,
Pad Length, and Certificate fields,) fields) in units of 8 octets.

Cert Type

The type of the certificate included in the Certificate field.
This specification defines only one legal value for this field:

1 X.509v3 Certificate, as specified below

Pad Length

The number of padding octets beyond the end of the Certificate
field but within the length specified by the Length field.
Padding octets MUST be set to zero by senders and ignored by
receivers.

Certificate

When the Cert Type field is set to 1, the Certificate field
contains an X.509v3 certificate [10], as described in Section
6.1.1.

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6.2.5 Processing Rules for Routers

Routers SHOULD possess should be configured with a key pair and a certificate from
at least one certificate authority.

A router MUST silently discard any received Delegation Chain
Solicitation messages that do not satisfy all of conform to the following
validity checks:

o All requirements listed message format
defined in Section 6.2.1 are fulfilled.

o If the message includes an IP Authentication Header, the message
authenticates correctly. 6.2.1. The contents of the Reserved field, and of
any unrecognized options, MUST be ignored. Future,
backward-compatible changes to the protocol may specify the contents
of the Reserved field or add new options; backward-incompatible
changes may use different Code values. The contents of any defined
options that are not specified to be used with Router Solicitation
messages MUST be ignored and the packet processed in the normal
manner. The only defined option that may appear is the Trust Anchor
option. A solicitation that passes the

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"valid solicitation".

Routers SHOULD send advertisements in response to valid solicitations
received on an advertising interface. If the source address in the
solicitation was the unspecified address, the router MUST send the
response to the link-scoped All-Nodes multicast address. If the
source address was a unicast address, the router MUST send the
response to the Solicited-Node multicast address corresponding to the
source address. address, except when under load, as specified below. Routers
SHOULD NOT send Delegation Chain Advertisements more than
MAX_DCA_RATE times within a second. When there are more solicitations than this,
solicitations, the router SHOULD send the response to the All-Nodes
multicast address regardless of the source address that appeared in
the solicitation.

In an advertisement, the router SHOULD include suitable Certificate
options so that a delegation chain to the solicited trust anchor can
be established. The anchor is identified by the Trust Anchor option.
If the Trust Anchor option is represented as a DER Encoded X.501
Name, then the Name must be equal to the Subject field in the
anchor's certificate. If the Trust Anchor option is represented as
an FQDN, the FQDN must be equal to an FQDN in the subjectAltName
field of the anchor's certificate. The router SHOULD include the
Trust Anchor option(s) in the advertisement for which the delegation
chain was found.

If the router is unable to find a chain to the requested anchor, it
SHOULD send an advertisement without any certificates. In this case
the router SHOULD include the Trust Anchor options which were
solicited.

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6.2.6 Processing Rules for Hosts

Hosts SHOULD possess the public key and trust anchor name of at least
one certificate authority, they SHOULD possess their own key pair,
and they MAY posses a certificate possess certificates from the above mentioned certificate authority. authorities.

A host MUST silently discard any received Delegation Chain
Advertisement messages that do not satisfy all of conform to the following
validity checks:

o All requirements listed message format
defined in Section 6.2.2 are fulfilled.

o If the message includes an IP Authentication Header, the message
authenticates correctly. 6.2.2. The contents of the Reserved field, and of
any unrecognized options, MUST be ignored. Future,
backward-compatible changes to the protocol

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may MAY specify the contents
of the Reserved field or add new options; backward-incompatible
changes may MUST use different Code values. The contents of any defined
options that are not specified to be used with Delegation Chain
Advertisement messages MUST be ignored and the packet processed in
the normal manner. The only defined options that may appear are the
Certificate and Trust Anchor options. An advertisement that passes
the validity checks is called a "valid advertisement".

Hosts SHOULD store certificate chains retrieved in Delegation Chain
Discovery messages if they start from an anchor trusted by the host.
The certificate chains SHOULD MUST be verified, as defined in Section 6.1,
before storing them. Routers MUST send the certificates one by one,
starting from the trust anchor end of the chain. Except for
temporary purposes to allow for message loss and reordering, hosts
SHOULD NOT store certificates received in a Delegation Chain
Advertisement unless they contain a certificate which can be
immediately verified either to the trust anchor or to a certificate
which
that has been verified earlier.

Note that it may be useful to cache caching this information and the implied verification
results between network attachments for use over multiple attachments
to the
network. network can help improve performance. But periodic
certificate revocation checks are still needed even with cached
results, to make sure that the certificates are still valid.

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
in the hosts' cache of certificates, or there is no authorization
delegation chain to the host's trust anchor. In these situations,
the host MAY transmit up to MAX_DCS_MESSAGES Delegation Chain
Solicitation messages, each separated by at least DCS_INTERVAL
seconds.

Delegation Chain Solicitations SHOULD NOT be sent if the host has a
currently valid certificate chain from a reachable router to a trust
anchor.

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When soliciting certificates for a router, a host MUST send
Delegation Chain Solicitations either to the All-Routers multicast
address, if it has not selected a default router yet, or to the
default router's IP address, if it a default router has already been
selected.

If two hosts want to establish trust with the DCS and DCA messages,
the DCS message SHOULD be sent to the Solicited-Node multicast
address of the receiver. The advertisements SHOULD be sent as
specified above for routers. However, the exact details are left for
a future outside
the scope of this specification.

When processing possible advertisements sent as responses to a

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solicitation, the host MAY prefer to process first those
advertisements with the same Identifier field value as in the
solicitation. This makes Denial-of-Service attacks against the
mechanism harder (see Section 9.3).

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7. Addressing

7.1 CGA Addresses CGAs

Nodes that use stateless address autoconfiguration, autoconfiguration SHOULD generate a
new CGA as specified in Section 4 of [12] for [13] each new time they run the
autoconfiguration run. procedure. The nodes MAY continue to use the same
public key and modifier, and start the process from Step 4. 4 of the
generation algorithm.

By default, a SEND-enabled node SHOULD use only CGAs as for its own
addresses. Other types of addresses MAY be used in testing,
diagnostics or for other purposes. However, this document does not
describe how to choose between different types of addresses for
different communications. A dynamic selection can be provided by an
API, such as the one defined in [22]. [23].

7.2 Redirect Addresses

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.

Note that RFC 2461 rules prevent a bogus router host from sending accepting a Redirect
message from a router that is not its default router. This prevents
an attacker from tricking a node into redirecting traffic when the host
attacker 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, nodes SHOULD verify that the prefix
specified in this option falls within the range defined by the
certificate, if the certificate contains advertise securely. A router MAY, however, advertise a prefix extension. Options
failing this check MUST be silently discarded.

Nodes SHOULD use one
combination of the certified prefixes for stateless
autoconfiguration. If none of the advertised prefixes match, then
either there is a configuration problem or the advertising router is
an attacker, and uncertified prefixes. Uncertified
prefixes are treated as insecure, i.e., processed in the host MUST use a different advertising router same way as
its default
insecure router (if available). If the node is performing
stateful autoconfiguration, it SHOULD check the address provided advertisements sent by
the DHCP server against the certified prefixes and MUST NOT use the
address if the prefix non-SEND routers. The
processing of insecure messages is specified in Section 8. Note that
SEND nodes that do not certified.

In any case, the user should inform attempt to interoperate with non-SEND nodes
MAY simply discard the network operator upon

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receiving an address or prefix outside insecure information.

Certified prefixes fall into the certified range, since
this is either a misconfiguration or an attack. following two categories:

Constrained

If the network operator wants to constrain which routers are
allowed to route particular prefixes, routers SHOULD should be configured

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with certificates having prefixes listed in the prefix extension.
Routers so configured MUST SHOULD advertise the prefixes which they are
certified to route, or a subset thereof.

Unconstrained

Network operators that do not want to constrain routers this way
SHOULD
should configure routers with certificates containing either the
null prefix or no prefix extension at all.

Upon processing a Prefix Information option within a Router
Advertisement, nodes SHOULD verify that the prefix specified in this
option falls within the range defined by the certificate, if the
certificate contains a prefix extension. Options failing this check
are treated as containing uncertified prefixes.

Nodes SHOULD use one of the certified prefixes for stateless
autoconfiguration. If none of the advertised prefixes match, the
host SHOULD use a different advertising router as its default router,
if available. If the node is performing stateful autoconfiguration,
it SHOULD check the address provided by the DHCP server against the
certified prefixes and SHOULD NOT use the address if the prefix is
not certified.

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 chain-based authorization specifications are
needed for such nodes.

It is outside the scope of this specification to describe the use of
trust anchor authorization between nodes with dynamically changing
addresses. Such dynamically changing addresses may be the result of
stateful or stateless address autoconfiguration, or through the use
of RFC 3041 [17] [18] addresses. If the CGA method is not used, nodes
would be required to exchange certificate chains that terminate in a
certificate authorizing a node to use an IP address having a
particular interface identifier. This specification does not specify
the format of such certificates, since there are currently a few
cases where such certificates are required by the link layer and it
is up to the link layer to provide certification for the interface
identifier. This may be the subject of a future specification. It
is also outside the scope of this specification to describe how
stateful address autoconfiguration works with the CGA method.

The Target Address in Neighbor Advertisement is required to be equal
to the source address of the packet, except in the case of proxy

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Neighbor Discovery. Proxy Neighbor Discovery is not supported by
this specification; it is planned to be specified in a future
document. specification.

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8. Transition Issues

During the transition to secure links or as a policy consideration,
network operators may want to run a particular link with a mixture of
secure and insecure nodes. Nodes that support SEND SHOULD support
the use of SEND and the legacy plain NDP at the same time.

In a mixed environment, SEND nodes receive both secure and insecure
messages but give priority to "secured" ones. Here, the "secured"
messages are ones that contain a valid signature option, as specified
above, and "insecure" messages are ones that contain no signature
option.

SEND nodes MUST send only secured messages. Legacy Plain (non-SEND)
Neighbor Discovery nodes will obviously send only insecure messages.
Per RFC 2461 [7], such nodes will ignore the unknown options and will
treat secured messages in the same way as they treat insecure ones.
Secured and insecure nodes share the same network resources, such as
prefixes and address spaces.

In a mixed environment SEND nodes follow the protocols defined in RFC
2461 and RFC 2462 with the following exceptions:

o All solicitations sent by a SEND nodes node MUST be secured.

o Unsolicited advertisements sent by a SEND node MUST be secured.

o A SEND node MUST send a secured advertisement in response to a
secured solicitation. Advertisements sent in response to an
insecure solicitation MUST be secured as well, but MUST NOT
contain the Nonce option.

o A SEND node that uses the CGA authorization method for protecting
Neighbor Solicitations SHOULD perform Duplicate Address Detection
as follows. If Duplicate Address Detection indicates the
tentative address is already in use, generate a new tentative CGA
address. CGA.
If after 3 consecutive attempts no non-unique address was
generated, log a system error and give up attempting to generate
an address for that interface.

When performing Duplicate Address Detection for the first
tentative address, accept both secured and insecure Neighbor
Advertisements and Solicitations received as response to the
Neighbor Solicitations. When performing Duplicate Address
Detection for the second or third tentative address, ignore
insecure Neighbor Advertisements and Solicitations.

o The node SHOULD MAY have a configuration option that causes it to ignore

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ignore

insecure advertisements even when performing Duplicate Address
Detection for the first tentative address. This configuration
option SHOULD be disabled by default. This is a recovery
mechanism, in case attacks against the first address become
common.

o The Neighbor Cache, Prefix List and Default Router list entries
MUST have a secured/insecure flag that indicates whether the
message that caused the creation or last update of the entry was
secured or insecure. Received insecure messages MUST NOT cause
changes to existing secured entries in the Neighbor Cache, Prefix
List or Default Router List. The Neighbor Cache SHOULD implement
a flag on entries indicating whether the entry issecured.
Received secured messages MUST cause an update of the matching
entries and flagging of them as secured.

o The conceptual sending algorithm is modified so that an insecure
router is selected only if there is no reachable SEND router for
the prefix. That is, the algorithm for selecting a default router
favors reachable SEND routers over reachable non-SEND ones.

o A SEND node SHOULD have a configuration option that causes it to
ignore all insecure Neighbor Solicitation and Advertisement,
Router Solicitation and Advertisement, and Redirect messages.
This can be used to enforce SEND-only networks.

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9. Security Considerations

9.1 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,
there is no assurance that payload packets actually come from the
same peer that the NDP was run against.

There may be no cryptographic binding in SEND between the link layer
frame address and the IPv6 address. On an insecure link layer that
allows nodes to spoof the link layer address of other nodes, an
attacker could disrupt IP service by sending out a Neighbor
Advertisement having the source address on the link layer frame of a
victim, a valid CGA address and a valid signature corresponding to
itself, and a Target Link-layer Address extension corresponding to
the victim. The attacker could then proceed to cause a traffic
stream to bombard the victim in a DoS attack. This attack cannot be
prevented just by securing the link layer.

Even on a secure link layer, SEND does not require that the addresses
on the link layer and Neighbor Advertisements correspond to each
other. However, it is RECOMMENDED that such checks be performed
where this is possible on the given link layer technology.

Prior to participating in Neighbor Discovery and Duplicate Address
Detection, nodes must subscribe to the link-scoped All-Nodes
Multicast Group and the Solicited-Node Multicast Group for the
address that they are claiming for their addresses; RFC 2461 [7].
Subscribing to a multicast group requires that the nodes use MLD
[16].
[17]. MLD contains no provision for security. An attacker could
send an MLD Done message to unsubscribe a victim from the
Solicited-Node Multicast address. However, the victim should be able
to detect such an attack because the router sends a
Multicast-Address-Specific Query to determine whether any listeners
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
router on the link has not been compromised. Other attacks using MLD
are possible, but they primarily lead to extraneous (but not
overwhelming) traffic.

9.2 How SEND Counters Threats to NDP

The SEND protocol is designed to counter the threats to NDP, as
outlined in [25]. [24]. The following subsections contain a regression of
the SEND protocol against the threats, to illustrate what aspects of
the protocol counter each threat.

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9.2.1 Neighbor Solicitation/Advertisement Spoofing

This threat is defined in Section 4.1.1 of [25]. [24]. The threat is that
a spoofed message may cause a false entry in a node's Neighbor Cache.
There are two cases:

1. Entries made as a side effect of a Neighbor Solicitation or
Router Solicitation. A router receiving a Router Solicitation
with a firm IPv6 source address and a Target Link-Layer Address extension and the IPv6 source
address not equal to the unspecified address inserts an entry for
the IPv6 address into its Neighbor Cache. Also, a node
performing Duplicate Address Detection (DAD) that receives a
Neighbor Solicitation for the same address regards the situation
as a collision and ceases to solicit for the address.

In either case, SEND counters these treats by requiring the
Signature and CGA options to be present in such solicitations.

SEND nodes can send Router Solicitation messages with a CGA
source address and a CGA option, which the router can verify, so
the Neighbor Cache binding is correct. If a SEND node must send
a Router Solicitation with the unspecified address, the router
will not update its Neighbor Cache, as per RFC 2461.

2. Entries made as a result of a Neighbor Advertisement message.
SEND counters this threat by requiring the Signature and CGA
options to be present in these advertisements.

See also Section 9.2.5, below, for discussion about replay protection
and timestamps.

9.2.2 Neighbor Unreachability Detection Failure

This attack is described in Section 4.1.2 of [25]. [24]. SEND counters
this attack by requiring a node responding to Neighbor Solicitations
sent as NUD probes to include a Signature option and proof of
authorization to use the interface identifier in the address being
probed. If these prerequisites are not met, the node performing NUD
discards the responses.

9.2.3 Duplicate Address Detection DoS Attack

This attack is described in Section 4.1.3 of [25]. [24]. SEND counters
this attack by requiring the Neighbor Advertisements sent as
responses to DAD to include a Signature option and proof of
authorization to use the interface identifier in the address being
tested. If these prerequisites are not met, the node performing DAD
discards the responses.

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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
Advertisements that performing DAD, it may be send by the listen for address
collisions from non-SEND nodes. nodes for the first address it generates,
but not for new attempts. This protects 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 collision between a SEND node and
non-SEND node. The probability and effects of such an address
collision are discussed in [12]. [13].

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,
and 4.2.7 of [25]. [24]. SEND counters these attacks by requiring Router
Advertisements to contain a Signature option, and that the signature
is calculated using the public key of a node that can prove its
authorization to route the subnet prefixes contained in any Prefix
Information Options. The router proves its authorization by showing
a certificate containing the specific prefix or the indication that
the router is allowed to route any prefix. A Router Advertisement
without these protections is discarded.

SEND does not protect against brute force attacks on the router, such
as DoS attacks, or compromise of the router, as described in Sections
4.4.2 and 4.4.3 of [25]. [24].

9.2.5 Replay Attacks

This attack is described in Section 4.3.1 of [25]. [24]. SEND protects
against attacks in Router Solicitation/Router Advertisement and
Neighbor Solicitation/Neighbor Advertisement transactions by
including a Nonce option in the solicitation and requiring the
advertisement to include a matching option. Together with the
signatures this forms a challenge-response protocol. SEND protects
against attacks from unsolicited messages such as Neighbor
Advertisements, Router Advertisements, and Redirects by including a
Timestamp option. A window of vulnerability for replay attacks
exists until the timestamp expires.

When timestamps are used, SEND nodes are protected against replay
attacks as long as they cache the state created by the message
containing the timestamp. The cached state allows the node to
protect itself against replayed messages. However, once the node
flushes the state for whatever reason, an attacker can re-create the
state by replaying an old message while the timestamp is still valid.
Since most SEND nodes are likely to use fairly coarse grained
timestamps, as explained in Section 5.3.1, this may affect some
nodes.

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9.2.6 Neighbor Discovery DoS Attack

This attack is described in Section 4.3.2 of [25]. [24]. In this attack,
the attacker bombards the router with packets for fictitious
addresses on the link, causing the router to busy itself with
performing Neighbor Solicitations for addresses that do not exist.
SEND does not address this threat because it can be addressed by
techniques such as rate limiting Neighbor Solicitations, restricting
the amount of state reserved for unresolved solicitations, and clever
cache management. These are all techniques involved in implementing
Neighbor Discovery on the router.

9.3 Attacks against SEND Itself

The CGAs have a 59-bit hash value. The security of the CGA mechanism
has been discussed in [12]. [13].

Some Denial-of-Service attacks against NDP and SEND itself remain.
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
methods. While safeguards are required to prevent an excessive use
of resources, this can still render SEND non-operational.

When CGA protection is used, SEND deals with the DoS attacks using
the verification process described in Section 5.2.2. In this
process, a simple hash verification of the CGA property of the
address is performed before performing the more expensive signature
verification. However, even if the CGA verification succeeds, no
claims about the validity of the message can be made, until the
signature has been checked.

When trust anchors and certificates are used for address validation
in SEND, the defenses are not quite as effective. Implementations
SHOULD track the resources devoted to the processing of packets
received with the Signature option, and start selectively discarding
packets if too many resources are spent. Implementations MAY also
first discard packets that are not protected with CGA.

The Authorization Delegation Discovery process may also be vulnerable
to Denial-of-Service attacks. An attack may target a router by
requesting a large number of delegation chains to be discovered for
different trust anchors. Routers SHOULD defend against such attacks
by caching discovered information (including negative responses) and
by limiting the number of different discovery processes they engage
in.

Attackers may also target hosts by sending a large number of
unnecessary certificate chains, forcing hosts to spend useless memory

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and verification resources for them. Hosts can defend against such
attacks by limiting the amount of resources devoted to the

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certificate chains and their verification. Hosts SHOULD also
prioritize advertisements that sent as a response to their
solicitations above unsolicited advertisements.

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10. Protocol Constants

Host constants:

MAX_DCS_MESSAGES 3 transmissions
DCS_INTERVAL 4 seconds

Router constants:

MAX_DCA_RATE 10 times per second

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11. Protocol Variables

TIMESTAMP_DELTA 3,600 seconds (1 hour)
TIMESTAMP_FUZZ 1 second
TIMESTAMP_DRIFT 1 % (0.01)

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12. IANA Considerations

This document defines two new ICMP message types, used in
Authorization Delegation Discovery. These messages must be assigned
ICMPv6 type numbers from the informational message range:

o The Delegation Chain Solicitation message, described in Section
6.2.1.

o The Delegation Chain Advertisement message, described in Section
6.2.2.

This document defines six new Neighbor Discovery Protocol [7]
options, which must be assigned Option Type values within the option
numbering space for Neighbor Discovery Protocol messages:

o The CGA option, described in Section 5.1.

o The Signature option, described in Section 5.2.

o The Timestamp option, described in Section 5.3.1.

o The Nonce option, described in Section 5.3.2.

o The Trust Anchor option, described in Section 6.2.3.

o The Certificate option, described in Section 6.2.4.

This document defines a new 128-bit value under the CGA Message Type
[12]
[13] namespace, 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08.

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
using standards action 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
Certificate option. Future values of this field can be allocated
using standards action Standards Action [6]. The current values for this field are:

1 X.509v3 Certificate

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Normative References

[1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.

[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[3] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.

[4] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.

[5] Piper, D., "The Internet IP Security Domain of Interpretation
for ISAKMP", RFC 2407, November 1998.

[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.

[7] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.

[8] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.

[9] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.

[10] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.

[11] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing
Domain Names in Applications (IDNA)", RFC 3490, March 2003.

[12] Lynn, C., Kent, S. and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers",
draft-ietf-pkix-x509-ipaddr-as-extn-03 (work in progress),
September 2003.

[12]

[13] Aura, T., "Cryptographically Generated Addresses (CGA)",
draft-ietf-send-cga-03 (work in progress), December 2003.

[13]

[14] RSA Laboratories, "RSA Encryption Standard, Version 2.1", PKCS
1, November 2002.

[14]

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[15] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-1, April 1995, <http://

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www.itl.nist.gov/fipspubs/fip180-1.htm>.

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Informative References

[15]

[16] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.

[16]

[17] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.

[17]

[18] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.

[18]

[19] Farrell, S. and R. Housley, "An Internet Attribute Certificate
Profile for Authorization", RFC 3281, April 2002.

[19] Hinden, R.

[20] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and S. Deering, "Internet M.
Carney, "Dynamic Host Configuration Protocol Version 6 (IPv6)
Addressing Architecture", for IPv6
(DHCPv6)", RFC 3513, April 3315, July 2003.

[20]

[21] Arkko, J., "Effects of ICMPv6 on IKE and IPsec Policies",
draft-arkko-icmpv6-ike-effects-02 (work in progress), March
2003.

[21]

[22] Arkko, J., "Manual SA Configuration for IPv6 Link Local
Messages", draft-arkko-manual-icmpv6-sas-01 (work in progress),
June 2002.

[22]

[23] Nordmark, E., Chakrabarti, S. and J. Laganier, "IPv6 Socket API
for Address Selection", draft-chakrabarti-ipv6-addrselect-02
(work in progress), October 2003.

[23] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002.

[24] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-06 (work in progress), July 2003.

[25] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
Discovery trust models and threats", draft-ietf-send-psreq-00 draft-ietf-send-psreq-04
(work in progress), October
2002.

[26] International Organization for Standardization, "The Directory
- Authentication Framework", ISO Standard X.509, 2000.

[27] Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access Control",
IEEE Standard 802.1X, September 2001. 2003.

Authors' Addresses

Jari Arkko
Ericsson

Jorvas 02420
Finland

EMail: jari.arkko@ericsson.com

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Authors' Addresses

Jari Arkko
Ericsson

Jorvas 02420
Finland

EMail: jari.arkko@ericsson.com

James Kempf
DoCoMo Communications Labs USA
181 Metro Drive
San Jose, CA 94043
USA

EMail: kempf@docomolabs-usa.com

Bill Sommerfeld
Sun Microsystems
1 Network Drive UBUR02-212
Burlington, MA 01803
USA

EMail: sommerfeld@east.sun.com

Brian Zill
Microsoft

USA

EMail: bzill@microsoft.com

Pekka Nikander
Ericsson

Jorvas 02420
Finland

EMail: Pekka.Nikander@nomadiclab.com

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Appendix A. Contributors

Tuomas Aura contributed the transition mechanism specification in
Section 8. Jonathan Trostle contributed the certificate chain
example in Section 6.1.1.

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Appendix B. Acknowledgments

The authors would like to thank Tuomas Aura, Erik Nordmark, Gabriel
Montenegro, Pasi Eronen, Greg Daley, Jon Wood, Julien Laganier,
Francis Dupont, and Pekka Savola for interesting discussions in this
problem space and feedback regarding the SEND protocol.

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Appendix C. Cache Management

In this section we outline a cache management algorithm that allows a
node to remain partially functional even under a cache filling DoS
attack. This appendix is informational, and real implementations
SHOULD use different algorithms in order to avoid he dangers of
mono-cultural code.

There are at least two distinct cache related attack scenarios:

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
the nodes can continue to communicate even if the attack is going
on.

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
the new node to become attached to the network, in spite of the
attack.

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
discriminative against those nodes that have a large clock
difference, while an attacker can reduce its clock difference into
arbitrarily small. Throwing out old entries just because their clock
difference is large seems like a bad approach.

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
cache entries than old ones. One could track traffic, and only allow
those new entries that receive genuine traffic to be converted into
old cache entries. While such a scheme will make attacks harder, it
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
victim into promoting its cache entry to the old cache. Hence, the
node may be more intelligent in keeping its cache entries, and not
just have a black/white old/new boundary.

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
higher chance of staying in.

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This document and the information contained herein is provided on an
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