Network Working Group J. Arkko
Internet-Draft Ericsson
Expires: December 4, 2003 J. Kempf
DoCoMo Communications Labs USA
B. Sommerfeld
Sun Microsystems
B. Zill
Microsoft
P. Nikander
Ericsson
June 5, 2003
SEcure Neighbor Discovery (SEND)
draft-ietf-send-ipsec-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on December 4, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
IPv6 nodes use the Neighbor Discovery (ND) protocol to discover other
nodes on the link, to determine each other's link-layer addresses, to
find routers and to maintain reachability information about the paths
to active neighbors. If not secured, ND protocol is vulnerable to
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various attacks. This document specifies an extension to IPsec for
securing ND. Contrary to the original ND specifications that also
called for use of IPsec, this extension does not require the creation
of a large number of manually configured security associations.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Neighbor and Router Discovery Overview . . . . . . . . . . 7
4. Secure Neighbor Discovery Overview . . . . . . . . . . . . 10
5. Modifications to Neighbor Discovery . . . . . . . . . . . 12
5.1 Unspecified Source Address . . . . . . . . . . . . . 12
5.2 Secure-Solicited-Node Multicast Address . . . . . . 12
5.3 Nonce Option . . . . . . . . . . . . . . . . . . . . 13
5.4 Proxy Neighbor Discovery . . . . . . . . . . . . . . 14
6. Authorization Delegation Discovery . . . . . . . . . . . . 15
6.1 Delegation Chain Solicitation Message Format . . . . 15
6.2 Delegation Chain Advertisement Message Format . . . 17
6.3 Trusted Root Option . . . . . . . . . . . . . . . . 19
6.4 Certificate Option . . . . . . . . . . . . . . . . . 20
6.5 Router Authorization Certificate Format . . . . . . 21
6.5.1 Field Values . . . . . . . . . . . . . . . . .22
6.6 Processing Rules for Routers . . . . . . . . . . . . 23
6.7 Processing Rules for Hosts . . . . . . . . . . . . . 24
7. IPsec Extensions . . . . . . . . . . . . . . . . . . . . . 27
7.1 The AH_RSA_Sig Transform . . . . . . . . . . . . . . 27
7.1.1 Reserved SPI Number . . . . . . . . . . . . .27
7.1.2 Authentication Data Format . . . . . . . . . .27
7.1.3 AH_RSA_Sig Security Associations . . . . . . .29
7.1.4 Replay Protection . . . . . . . . . . . . . .30
7.1.5 Processing Rules for Senders . . . . . . . . .31
7.1.6 Processing Rules for Receivers . . . . . . . .32
7.2 Other IPsec Extensions . . . . . . . . . . . . . . . 33
7.2.1 Destination Agnostic Security Associations . .33
7.2.2 ICMP Type Specific Selectors . . . . . . . . .33
8. Securing Neighbor Discovery with SEND . . . . . . . . . . 34
8.1 Neighbor Solicitation Messages . . . . . . . . . . . 34
8.1.1 Sending Secure Neighbor Solicitations . . . .34
8.1.2 Receiving Secure Neighbor Solicitations . . .34
8.2 Neighbor Advertisement Messages . . . . . . . . . . 35
8.2.1 Sending Secure Neighbor Advertisements . . . .35
8.2.2 Receiving Secure Neighbor Advertisements . . .35
8.3 Other Requirements . . . . . . . . . . . . . . . . . 36
8.4 Configuration . . . . . . . . . . . . . . . . . . . 36
9. Securing Router Discovery with SEND . . . . . . . . . . . 39
9.1 Router Solicitation Messages . . . . . . . . . . . . 39
9.1.1 Sending Secure Router Solicitations . . . . .39
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9.1.2 Receiving Secure Router Solicitations . . . .39
9.2 Router Advertisement Messages . . . . . . . . . . . 39
9.2.1 Sending Secure Router Advertisements . . . . .40
9.2.2 Receiving Secure Router Advertisements . . . .40
9.3 Redirect Messages . . . . . . . . . . . . . . . . . 40
9.3.1 Sending Redirects . . . . . . . . . . . . . .40
9.3.2 Receiving Redirects . . . . . . . . . . . . .41
9.4 Other Requirements . . . . . . . . . . . . . . . . . 41
9.5 Configuration . . . . . . . . . . . . . . . . . . . 42
10. Co-Existence of SEND and ND . . . . . . . . . . . . . . . 44
10.1 Behavior Rules . . . . . . . . . . . . . . . . . . . 44
10.2 Configuration . . . . . . . . . . . . . . . . . . . 46
11. Performance Considerations . . . . . . . . . . . . . . . . 49
12. Implementation Considerations . . . . . . . . . . . . . . 50
13. Security Considerations . . . . . . . . . . . . . . . . . 51
13.1 Threats to the Local Link Not Covered by SEND . . . 51
13.2 How SEND Counters Threats to Neighbor Discovery . . 51
13.2.1 Neighbor Solicitation/Advertisement Spoofing .51
13.2.2 Neighbor Unreachability Detection Failure . .53
13.2.3 Duplicate Address Detection DoS Attack . . . .53
13.2.4 Router Solicitation and Advertisement Attacks 53
13.2.5 Replay Attacks . . . . . . . . . . . . . . . .53
13.2.6 Neighbor Discovery DoS Attack . . . . . . . .54
13.3 Attacks against SEND Itself . . . . . . . . . . . . 54
14. IANA Considerations . . . . . . . . . . . . . . . . . . . 56
Normative References . . . . . . . . . . . . . . . . . . . 57
Informative References . . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 60
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . 62
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 63
C. IPR Considerations . . . . . . . . . . . . . . . . . . . . 64
Intellectual Property and Copyright Statements . . . . . . 65
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1. Introduction
IPv6 defines the Neighbor Discovery (ND) protocol in RFC 2461 [6].
Nodes on the same link use the ND protocol 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. The ND protocol is used both by hosts and routers.
Its functions include Router Discovery (RD), Address Auto-
configuration, Address Resolution, Neighbor Unreachability Detection
(NUD), Duplicate Address Detection (DAD), and Redirection.
RFC 2461 called for the use of IPsec for protecting the ND messages.
However, it turns out that in this particular application IPsec can
only be used with a manual configuration of security associations due
to chicken-and-egg problems in using IKE [23, 21] before ND is
operational. Furthermore, the number of such manually configured
security associations needed for protecting ND is impractically large
[24]. Finally, RFC 2461 did not specify detailed instructions for
using IPsec to secure ND.
Section 4 describes our overall approach to securing ND. This
approach involves the use of IPsec AH [3] to secure all
advertisements relating to Neighbor and Router Discovery. A new
transform for AH allows public keys to be used. Routers are
certified by a trusted root, and a zero-configuration mechanism for
showing address ownership. The formats, procedures, and
cryptographic mechanisms for this zero-configuration mechanism are
described in a related specification [27].
Section 6 describes the mechanism for distributing certificate chains
to establish authorization delegation chain to a common trusted root.
Section 7 describes the necessary modifications to IPsec. Section 8
and Section 9 show how to apply these components to securing Neighbor
and Router Discovery. A few small changes are required in the
Neighbor Discovery protocol and these are discussed in Section 5.
Finally, Section 10 discusses the co-existence of secure and
non-secure Neighbor Discovery on the same link, Section 11 discusses
performance considerations, Section 12 discusses the implementation
considerations related to the IPsec extensions, and Section 13
discusses security considerations for SEND.
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2. Terms
Authorization Certificate (AC)
The signer of an authorization certificate has authorized the
entity designated in the certificate for a specific task or
service.
Authorization Delegation Discovery (ADD)
This is a process through which SEND nodes can acquire a
certificate chain from a peer node to a trusted root.
Cryptographically Generated Addresses (CGAs)
A technique [27, 30] where the address of the node is
cryptographically generated from the public key of the node and
some other parameters using a one-way hash function.
Duplicate Address Detection (DAD)
This mechanism defined in RFC 2462 [7] 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 is a part
of ICMPv6.
Neighbor Discovery (ND)
The IPv6 Neighbor Discovery protocol [6].
Neighbor Unreachability Detection (NUD)
This mechanism defined in RFC 2461 [6] is used for tracking the
reachability of neighbors.
Nonce
Nonces are random numbers generated by a node. In SEND, they are
used to ensure that a particular advertisement is linked to the
solicitation that triggered it.
Security association
A security association is a simplex "connection" that affords
security services to the traffic carried by it. Security services
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are afforded to a security association by the use of AH, or ESP,
but not both. A security association is uniquely identified by a
triple consisting of a Security Parameter Index (SPI), an IP
Destination Address, and a security protocol (AH or ESP)
identifier [2].
Security association database
A nominal database containing parameters that are associated with
each (active) security association. For inbound and outbound
IPsec processing, these databases are separate.
Security Parameters Index (SPI)
An arbitrary 32-bit value. Together with the destination IP
address and security protocol (ESP or AH) identifier, the SPI
uniquely identifies the Security Association. Values from 1 to
255 are reserved.
Special SPI
A Security Parameters Index from the reserved range 1 to 255.
Security policy
The security policy determines the security services afforded to
an IPsec protected packet and the treatment of the packet in the
network.
Security policy database
A nominal database containing a list of policy entries. Each
policy entry is keyed by one or more selectors that define the set
of IP traffic encompassed by this policy entry. Separate entries
for inbound and outbound traffic is required [2].
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3. Neighbor and Router Discovery Overview
IPv6 Neighbor and Router Discovery have several functions. Many of
these functions are overloaded on a few central message types such as
the ICMPv6 Neighbor Discovery message. In this section we explain
some of these tasks and their effects in order to understand better
how the messages should be treated. Where this section and the
original Neighbor Discovery RFCs are in conflict, the original RFCs
take precedence.
In IPv6, many of the tasks traditionally done at lower layers such as
ARP have been moved to the IP layer. As a consequence, unified
mechanisms can be applied across link layers, security mechanisms or
other extensions can be adopted more easily, and a clear separation
of the roles between the IP and link layer can be achieved.
The main functions of IPv6 Neighbor Discovery are as follows:
o Neighbor Unreachability Detection (NUD) is used for tracking the
reachability of neighbors, both hosts and routers. NUD is defined
in Section 7.3 of RFC 2461 [6]. NUD is security-sensitive,
because no higher level traffic can proceed if this procedure
flushes out neighbor cache entries after (perhaps incorrectly)
determining that the peer is not reachable.
o Duplicate Address Detection (DAD) is used for preventing address
collisions [7]. A node that intends to assign a new address to
one of its interfaces runs first the DAD procedure to verify that
other nodes are not using the same address. Since the outlined
rules forbid the use of an address until it has been found unique,
no higher layer traffic is possible until this procedure has
completed. Thus, preventing attacks against DAD can help ensure
the availability of communications for the node in question.
o Address Resolution is similar to IPv4 ARP [20]. The Address
Resolution function resolves a node's IPv6 address to the
corresponding link-layer address for nodes on the link. Address
Resolution is defined in Section 7.2 of RFC 2461 [6] and it is
used for hosts and routers alike. Again, no higher level traffic
can proceed until the sender knows the hardware address of the
destination node or the next hop router. Note that like its
predecessor in ARP, IPv6 Neighbor Discovery does not check the
source link layer address 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.
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o Address Autoconfiguration is used for automatically assigning
addresses to a host [7]. This allows hosts to operate without
configuration related to IP connectivity. The Address
Autoconfiguration mechanism is stateless, where the hosts use
prefix information delivered to them during Router Discovery to
create addresses, and then test these addresses for uniqueness
using the DAD procedure. A stateful mechanism, DHCPv6 [25],
provides additional Autoconfiguration features. Router and Prefix
Discovery and Duplicate Address Detection have an effect to the
Address Autoconfiguration tasks.
o The Redirect function is used for automatically redirecting hosts
to an alternate router. Redirect is specified in Section 8 of RFC
2461 [6]. It is similar to the ICMPv4 Redirect message [19].
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 [6]. 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 to the destination node directly.
Typically, address autoconfiguration and other tasks can not
proceed until suitable routers and prefixes have been found.
The Neighbor Discovery messages follow the ICMPv6 message format and
ICMPv6 types from 133 to 137. The IPv6 Next Header value for ICMPv6
is 58. The actual Neighbor Discovery message includes an ND message
header consisting of ICMPv6 header and ND message-specific data, and
zero or more ND options:
<------------ND Message----------------->
*-------------------------------------------------------------*
| IPv6 Header | ICMPv6 | ND message- | ND Message |
| Next Header = 58 | Header | specific | Options |
| (ICMPv6) | | data | |
*-------------------------------------------------------------*
<--ND Message header--->
The ND message options are formatted in the Type-Length-Value format.
All IPv6 ND protocol functions are realized using the following
messages:
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ICMPv6 Type Message
------------------------------------
133 Router Solicitation (RS)
134 Router Advertisement (RA)
135 Neighbor Solicitation (NS)
136 Neighbor Advertisement (NA)
137 Redirect
The functions of the ND protocol are realized using these messages as
follows:
o Router Discovery uses the RS and RA messages.
o Duplicate Address Detection uses the NS and NA messages.
o Address Autoconfiguration uses the NS, NA, RS, and RA messages.
o Address Resolution uses the NS and NA messages.
o Neighbor Unreachability Detection uses the NS and NA messages.
o Redirect uses the Redirect message.
The destination addresses used in these messages are as follows:
o Neighbor Solicitation: The destination address is either the
solicited-node multicast address, unicast address, or an anycast
address.
o Neighbor Advertisement: The destination address is either a
unicast address or the All Nodes multicast address [1].
o Router Solicitation: The destination address is typically the All
Routers multicast address [1].
o Router Advertisement: The destination address can be either a
unicast or the All Nodes multicast address [1]. Like the
solicitation message, the advertisement is also local to the link
only.
o Redirect: This message is always sent from the router's link-local
address to the source address of the packet that triggered the
Redirect. Hosts verify that the IP source address of the Redirect
is the same as the current first-hop router for the specified ICMP
Destination Address. Rules in [1] dictate that unspecified,
anycast, or multicast addresses may not be used as source
addresses. Therefore, the destination address will always be a
unicast address.
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4. Secure Neighbor Discovery Overview
IPsec AH is used in to protect Neighbor and Router Discovery
messages. This specification introduces the use of a new transform
for IPsec AH, extensions to the current IPsec selectors, an
authorization delegation discovery process, and an address ownership
proof mechanism.
The components of the solution specified in this document are as
follows:
o Trusted roots are expected to certify the authority of routers. A
host and a router must have at least one common trusted root
before the host can adopt the router as its default router.
Optionally, an authorization certificate can specify the prefixes
for which the router is allowed to act as a router. Delegation
Chain Solicitation and Advertisement messages are used to discover
a certificate chain to the trusted root without requiring the
actual Router Discovery messages to carry lengthy certificate
chains.
o Cryptographically Generated Addresses are used to assure that the
sender of a Neighbor or Router Advertisement is the owner of an
the claimed address. A public-private key pair needs to be
generated by all nodes before they can claim an address.
o IPsec AH is used to protect all messages relating to Neighbor and
Router discovery.
o IPsec security policy database and security association database
are configured to require the protection as indicated above. Note
that such configuration may take place manually or the operating
system may perform it automatically upon enabling Secure Neighbor
Discovery.
This specification introduces extensions to the required selectors
used in security policy database entries. This is necessary in
order to enable the protection of specific ICMP message types,
while leaving other messages unprotected.
o A new transform for IPsec AH allows public keys to be used on a
security association directly without the involvement of a key
management protocol. Symmetric session keys are not used, public
key signatures are used instead. The trust to the public key is
established either with the authorization delegation process or
the address ownership proof mechanism, depending on configuration
and the type of the message protected.
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The new transform uses also a fixed, standardized SPI (Security
Parameters Index) number. This is necessary again in order to
avoid the involvement of a key management protocol.
Given that Neighbor and Router Discovery messages are in some
cases sent to multicast addresses, the new transform uses
timestamps as a replay protection mechanism instead of sequence
numbers. To provide additional replay protection for the cases
where required clock accuracy is not available, nonces are used in
the Neighbor Discovery protocol.
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5. Modifications to Neighbor Discovery
Support for the SEND protocol can be added to a Neighbor Discovery
implementation by providing the new Neighbor Discovery protocol
mechanisms described in Section 6, the IPsec mechanisms described in
Section 7, and using them together as specified in Section 9 and
Section 8. However, the following aspects of the Neighbor Discovery
protocol change with SEND:
o The use of the unspecified address as a source address is
discouraged.
o The solicited-node multicast address is replaced with the
securely-solicited-node multicast address.
o The Nonce option is required in all Neighbor Discovery
solicitations, and for all solicited advertisements.
o Proxy Neighbor Discovery is not supported in this specification
(it will be specified in a future document).
5.1 Unspecified Source Address
In SEND, the unspecified address is not used as the source address in
Neighbor Solicitation, Neighbor Advertisement, Router Advertisement,
or Redirect messages. A Neighbor Solicitation sent as a part of
Duplicate Address Detection uses the tentative address for which the
Duplicate Address Detection is being run.
The use of the unspecified address is avoided in Router
Solicitations, if possible. RFC 2461 requires that Router
Solicitations sent from the unspecified address do not cause a
modification in the Neighbor Cache.
5.2 Secure-Solicited-Node Multicast Address
SEND defines the securely-solicited-node multicast addresses. These
addresses are of the form:
FF02:0:0:0:0:1:FEXX:XXXX
Like the solicited-node multicast address, this multicast address is
computed as a function of a node's unicast and anycast addresses.
The securely-solicited-node multicast address is formed by taking the
low-order 24 bits of the address (unicast or anycast) and appending
those bits to the prefix FF02:0:0:0:0:1:FE00::/104 resulting in a
multicast address in the range FF02:0:0:0:0:1:FE00:0000 to
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FF02:0:0:0:0:1:FEFF:FFFF.
As discussed in Section 8.1, SEND uses the securely-solicited-node
multicast address instead of the solicited-node multicast address
when sending secured Neighbor Solicitations. However, in order to
allow for co-existence of secure and insecure Neighbor Discovery on
the same link, SEND nodes will also send Duplicate Address Detection
probes to the solicited-node multicast address (see Section 10). The
use of two different addresses is necessary in order to distinguish
between these messages in the security policy database.
5.3 Nonce Option
The purpose of the Nonce option is to ensure that an advertisement is
a fresh response to a solicitation sent earlier by this same node.
The format of the Nonce option is as 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 | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
Type
TBD <To be assigned by IANA> for Nonce.
Length
The length of the option (including the Type, Length, and Nonce
fields) in units of 8 octets.
Nonce
This field contains a random number selected by the sender of the
solicitation message. The length of the number MUST be at least 6
bytes.
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5.4 Proxy Neighbor Discovery
The Target Address in Neighbor Advertisement is required to be equal
to the source address of the packet, except in the case of proxy
Neighbor Discovery. Proxy Neighbor Discovery is discussed in another
specification.
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6. Authorization Delegation Discovery
Several protocols, including IPv6 Neighbor Discovery, allow a node to
automatically configure itself based on information it learns shortly
after connecting to a new link. It is particularly easy for "rogue"
routers to be configured, and it is particularly difficult for a
network node to distinguish between valid and invalid sources of
information when the node needs this information before communicating
off-link.
Since the newly-connected node likely can not communicate off-link,
it can not be responsible for searching information to help validate
the router; 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.
Similarly, the router, which is already connected to the network, can
if necessary communicate off-link and construct the certificate
chain.
The Secure Neighbor Discovery protocol introduces two new ICMPv6
messages that are used between hosts and routers to allow the client
to learn the certificate chain with the assistance of the router.
Where hosts have certificates from a trusted root, these messages MAY
also optionally be used between hosts to acquire the peer's
certificate chain.
The Delegation Chain Solicitation message is sent by hosts when they
wish to request the certificate chain between a router and the one of
the hosts' trusted roots. The Delegation Chain Advertisement message
is sent as an answer to this message, or periodically to the All
Nodes multicast address. These messages are separate from the rest
of the Neighbor Discovery in order to reduce the effect of the
potentially voluminous certificate chain information to other
messages.
The Authorization Delegation Discovery process does not exclude other
forms of discovering the certificate chains. For instance, during
fast movements mobile nodes may learn information - including the
certificate chains - of the next router from the previous router.
6.1 Delegation Chain Solicitation Message Format
Hosts send Delegation Chain Solicitations in order to prompt routers
to generate Delegation Chain Advertisements quickly.
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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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
IP Fields:
Source Address
An IP address assigned to the sending interface, or the
unspecified address if no address is assigned to the sending
interface.
Destination Address
Typically the all-routers multicast address, the
securely-solicited-node multicast address (see Section 5.2, or
the address of the hosts' default router.
Hop Limit
255
ICMP Fields:
Type
TBD <To be assigned by IANA> for Delegation Chain Solicitation.
Code
0
Checksum
The ICMP checksum [8]..
Identifier
This 16 bit unsigned integer field acts as an identifier to
help match advertisements to solicitations. The Identifier
field MUST NOT be zero.
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Reserved
This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Valid Options:
Trusted Root
One or more trusted roots that the client is willing to accept.
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.
6.2 Delegation Chain Advertisement Message Format
Routers send out Delegation Chain Advertisement messages
periodically, or in response to a Delegation Chain Solicitation.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Component |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
IP Fields:
Source Address
MUST be a unicast address assigned to the interface from which
this message is sent.
Destination Address
Either the securely-solicited-node multicast address of the
receiver or the all-nodes multicast address.
Hop Limit
255
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ICMP Fields:
Type
TBD <To be assigned by IANA> for Delegation Chain
Advertisement.
Code
0
Checksum
The ICMP checksum [8]..
Identifier
This 16 bit unsigned integer field acts as an identifier to
help match advertisements to solicitations. The Identifier
field MUST be zero for unsolicited advertisements and MUST NOT
be zero for solicited advertisements.
Component
This is 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 taken in use before all the
components have arrived; this makes them slightly more reliable
and less prone to Denial-of-Service attacks. 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.
Reserved
This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Valid Options:
Certificate
One certificate is provided in Certificate option, to establish
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a (part of) certificate chain to a trusted root.
Trusted Root
Zero or more Trusted Root 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.
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.
6.3 Trusted Root Option
The format of the Trusted Root option is as 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 | Name Type | Name Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the fields are as follows:
Type
TBD <To be assigned by IANA> for Trusted Root.
Length
The length of the option (including the Type, Length, Name Type,
Name Length, and Name fields) in units of 8 octets.
Name Type
The type of the name included in the Name field. This
specification defines only one legal value for this field:
1 FQDN
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Name Length
The length of the Name field, in bytes. Octets beyond this length
but within the length specified by the Length field are padding
and 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 the
Fully Qualified Domain Name of the trusted root, for example
"trustroot.operator.com".
6.4 Certificate Option
The format of the certificate option is as 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> for Certificate.
Length
The length of the option (including the Type, Length, Cert Type,
Pad Length, and Certificate fields) in units of 8 octets.
Cert Type
The type of the certificate included in the Name field. This
specification defines only one legal value for this field:
1 X.509 Certificate
Pad Length
The amount of padding beyond the end of the Certificate field but
within the length specified by the Length field. Padding MUST be
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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.509 certificate [16].
6.5 Router Authorization Certificate Format
The certificate chain of a router terminates in a router
authorization certificate that authorizes a specific IPv6 node as a
router. Because authorization chains are not common practice in the
Internet at the time this specification is being written, the chain
MUST consist of standard Public Key Certificates (PKC, in the sense
of [11]) for identity from the trusted root shared with the host to
the router. This allows the host to anchor trust for the router's
public key in the trusted root. The last item in the chain is an
Authorization Certificate (AC, in the sense of [12]) authorizing the
router's right to route. Stronger certification is necessary here
than for CGAs because the right to route must be granted by an
authorizing agency. Future versions of this specification may
include provision for full authorization certificate chains, should
they become common practice.
SEND nodes MUST support the RFC 3281 X.509 attribute certificate
format [12] as the default format for router authorization
certificates, and MAY support other formats. Router authorization
certificates MUST be signed by the network operator or other trusted
third party whose PKC is above the router's PKC in the delegation
chain. Routers MAY advertise multiple ACs if the trust delegation
obtains from different trust roots, and the authorized prefixes in
those certificates MAY be disjoint. A router SHOULD only advertise
one AC corresponding to one trust root and all interfaces and
prefixes covered by that trust root MUST be in the AC.
In the attribute certificate, the GeneralName type MUST be either a
dNSName or iPAddress for the router, unless otherwise specified by
RFC 3281. If the GeneralName attribute is a dNSName, it MUST be
resolvable to a global unicast address assigned to the router. If
the GeneralName attribute is an iPAddress, it MUST be a global
unicast address assigned to the router. For purposes of facilitating
renumbering, a dNSName SHOULD be used. However, hosts MUST NOT use a
dNSName or iPAddress for validating the certificate. The router's
public key hash, stored in the
acinfo.holder.objectDigestInfo.objectDigest field of the certificate
provides the definitive validation. As explained in Section 9.2, the
addresses from the certificate can be matched against the global
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addresses claimed in the Router Advertisement.
6.5.1 Field Values
acinfo.holder.entityName
This field MAY contain one or several entityNames, of type dNSName
or iPAddress, referring to global address(es) belonging to the
router.
acinfo.objectDigestInfo.digestedObjectType
This field MUST be present and of type (1), publicKey.
acinfo.holder.digestAlgorithm
This field MUST indicate id-sha1 as indicated in RFC 3279 [10].
acinfo.objectDigestInfo.objectDigest
This field MUST be a SHA-1 digest over either a PKCS#1 [17] (RSA)
or an RFC 3279 Section 2.3.2 representation [10] (DSA)
representation of the router's public key. If this digest does
not match the digest of the router's public key from its PKC, a
node MUST discard the certificate.
acinfo.issuer.v2form.issuerName
The field MUST contain the distinguished name from the PKC used to
sign the router AC.
acinfo.attrCertValidityPeriod
A node MUST NOT accept a certificate if the validity period has
ended or has not yet started.
acinfo.attributes
This field MUST contain a list of prefixes that the router is
authorized to route, or the unspecified prefix if the router
is allowed to route any prefix. The field has the following
type:
name: AuthorizedSubnetPrefix
OID: {id-rcert}
Syntax: iPAddress
values: Multiple allowed
Multiple prefix values are allowed.
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The details of the above syntax are specified in Section 2.2.3.8
of [14].
If the router is authorized only to route specific prefixes, the
ipAddress values consist of IPv6 addresses in standard RFC 3513
[13] prefix format. One iPAddress value appears for each prefix
routed by the router. If the router is authorized to route any
prefix, a single ipAddress value appears with the value of the
unspecified address.
6.6 Processing Rules for Routers
Routers SHOULD possess a key pair and certificate from at least one
certificate authority.
A router MUST silently discard any received Delegation Chain
Solicitation messages that do not satisfy all of the following
validity checks:
o The IP Hop Limit field has a value of 255, i.e., the packet could
not possibly have been forwarded by a router.
o If the message includes an IP Authentication Header, the message
authenticates correctly.
o ICMP Checksum is valid.
o ICMP Code is 0.
o ICMP length (derived from the IP length) is 8 or more octets.
o Identifier field is non-zero.
o All included options have a length that is greater than zero.
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 Trusted Root option. A solicitation that passes the
validity checks is called a "valid solicitation".
Routers MAY send unsolicited Delegation Chain Advertisements for
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their trusted root. When such advertisements are sent, their timing
MUST follow the rules given for Router Advertisements in RFC 2461
[6]. The only defined option that may appear is the Certificate
option. At least one such option MUST be present. Router SHOULD
also include at least one Trusted Root option to indicate the trusted
root on which the Certificate is based.
In addition to sending periodic, unsolicited advertisements, a router
sends advertisements in response to valid solicitations received on
an advertising interface. A router MUST send the response to the
all-nodes multicast address, if the source address in the
solicitation was the unspecified address. If the source address was
a unicast address, the router MUST send the response to the
securely-solicited-node multicast address corresponding to the source
address.
In a solicited advertisement, the router SHOULD include suitable
Certificate options so that a delegation chain to the solicited root
can be established. The root is identified by the FQDN from the
Trusted Root option being equal to an FQDN in the AltSubjectName
field of the root's certificate. The router SHOULD include the
Trusted Root option(s) in the advertisement for which the delegation
chain was found.
If the router is unable to find a chain to the requested root, it
SHOULD send an advertisement without any certificates. In this case
the router SHOULD include the Trusted Root options which were
solicited.
Rate limitation of Delegation Chain Advertisements is performed as
specified for Router Advertisements in RFC 2461 [6].
6.7 Processing Rules for Hosts
Hosts SHOULD possess the certificate of at least one certificate
authority, and MAY possess their own key pair and certificate from
this authority.
A host MUST silently discard any received Delegation Chain
Advertisement messages that do not satisfy all of the following
validity checks:
o IP Source Address is a unicast address. Note that routers may use
multiple addresses, so this address not sufficient for the unique
identification of routers.
o IP Destination Address is either the all-nodes multicast address
or the securely-solicited-node multicast address corresponding to
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one of the unicast addresses assigned to the host.
o The IP Hop Limit field has a value of 255, i.e., the packet could
not possibly have been forwarded by a router.
o If the message includes an IP Authentication Header, the message
authenticates correctly.
o ICMP Checksum is valid.
o ICMP Code is 0.
o ICMP length (derived from the IP length) is 16 or more octets.
o All included options have a length that is greater than zero.
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 Delegation Chain Advertisement messages MUST be ignored and the
packet processed in the normal manner. The only defined option that
may appear is the Certificate option. An advertisement that passes
the validity checks is called a "valid advertisement".
Hosts SHOULD store all certificates retrieved in Delegation Chain
Advertisements for use in subsequent verification of Neighbor
Discovery messages. Note that it may be useful to cache this
information and implied verification results for use over multiple
attachments to the network. In order to use an advertisement for the
verification of a specific Neighbor Discovery message, the host
matches the key hash in acinfo.Holder.objectDigestInfo to the public
key carried in the IPsec AH Authentication Data field.
When an interface becomes enabled, a host may be unwilling to wait
for the next unsolicited Delegation Chain Advertisement. To obtain
such advertisements quickly, a host SHOULD transmit up to
MAX_RTR_SOLICITATIONS Delegation Chain Solicitation messages each
separated by at least RTR_SOLICITATION_INTERVAL seconds. Delegation
Chain Solicitations SHOULD be sent after any of the following events:
o The interface is initialized at system startup time.
o The interface is reinitialized after a temporary interface failure
or after being temporarily disabled by system management.
o The system changes from being a router to being a host, by having
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its IP forwarding capability turned off by system management.
o The host attaches to a link for the first time.
o A movement has been indicated by lower layers or has been inferred
from changed information in a Router Advertisement.
o The host re-attaches to a link after being detached for some time.
o 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 trusted root.
Delegation Chain Solicitations MUST NOT be sent if the host has a
currently valid certificate chain for the router to a trusted root,
including the Attribute Certificate for the desired router (or host).
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 has already
been selected.
If two hosts communicate with the solicitations and advertisements,
the solicitations MUST be sent to the securely-solicited-node
multicast address of the receiver. The advertisements MUST be sent
as specified above for routers.
Delegation Chain Solicitations SHOULD be rate limited and timed
similarly with Router Solicitations, as specified in RFC 2461 [6].
When processing a possible advertisement sent as a response to a
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 13.3).
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7. IPsec Extensions
In order to use IPsec in securing Neighbor and Router Discovery some
extensions have been specified in this document. These include a new
transform suitable for the use of public keys and/or CGAs, a
timestamp mechanism suitable for replay protection in a multicast
environment, and some extensions to security association and security
policy databases.
These changes are related to the proposed new transform and the
reserved SPI number, and do not represent a fundamental change to the
IPsec architecture. Some of the changes, such as the treatment of
destination addresses, are also being proposed as a part of the
revision of the IPsec standards.
7.1 The AH_RSA_Sig Transform
The AH_RSA_Sig transform specifies how AH can be used without a
symmetric key. This transform introduces the use of a new reserved
SPI number and a new format for the Authentication Data field in AH.
AH_RSA_Sig MUST NOT be negotiated in IKE. For consistency it has an
IPsec DOI [4] Transform ID TBD <To Be Assigned by IANA>, however.
7.1.1 Reserved SPI Number
The AH_RSA_Sig MUST be only be used with the reserved SPI number TBD
<To Be Assigned by IANA>.
7.1.2 Authentication Data Format
The format of the Authentication Data field in AH depends on the
chosen transform. For the AH_RSA_Sig transform, the format is as
follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Key Information .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Digital Signature (remaining bytes) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The meaning of the fields is described below:
Timestamp
This 64 bit unsigned integer field contains a timestamp used for
replay protection (the Sequence Number field in AH is not used for
AH_RSA_Sig). The use of this field is discussed in Section 7.1.4.
Key Information
This variable length field contains the public key of the sender.
It also may contain some other additional information which is
necessary when CGA is used.
The contents of the Key Information field are represented as ASN.1
DER-encoded data item of the following type:
SendKeyInformation ::= SEQUENCE {
cgaParameters CGAParameters OPTIONAL,
signerInfo SubjectPublicKeyInfo OPTIONAL }
CGAParameters ::= SEQUENCE {
publicKey SubjectPublicKeyInfo,
auxParameters CGAAuxParameters OPTIONAL }
(The normative definition of the type CGAParameters is in in
[27]).
At least one or both fields in SendKeyInformation MUST be present.
The packet MUST be silently discarded if both are missing. The
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verification of the CGA is based on the contents of the
cgaParameters field. The verification of the Digital Signature
field is based on the contents of the signerInfo field if it is
present. Otherwise, the verification is based on the publicKey
field in the cgaParameters field.
This specification requires that if both cgaParameters and
signerInfo fields are present, then the public keys in them MUST
be the same, and 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.
Digital Signature
This variable length field contains the signature made using the
sender's private key, over the the whole packet as defined by the
usual AH rules [3]. The signature is made using the RSA algorithm
and MUST be encoded as private key encryption in PKCS #1 format
[17].
The length of this field is determined by the PKCS #1 encoding.
7.1.3 AH_RSA_Sig Security Associations
Incoming security associations that specify the use of AH_RSA_Sig
transform MUST record the following additional configuration
information:
CGA flag
A flag that indicates whether or not the CGA property must be
verified.
router authority
Whether or not router authority must be verified as described in
Section 6.5.
root
The public key of the trusted root, if authorization delegation is
in use.
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minbits
The minimum acceptable key length for peer public keys (and any
intermediaries between the trusted root and the peer). The
default SHOULD be 768 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.
minSec
The minimum acceptable Sec value, if CGA verification is required
(see Section 2 in [27].
Outgoing security associations MUST also record the following
additional information:
keypair
A public-private key pair. If authorization delegation is in use,
there must exist a delegation chain from a trusted root to this
key pair.
CGA flag
A flag that indicates whether or not the CGA is used.
CGA parameters
Optionally any information required to construct CGAs, including
the used Sec value and nonce, and the CGA itself.
7.1.4 Replay Protection
For AH_RSA_Sig, the Sequence Number field in AH MUST be set to zero
by the sender and ignored by receivers.
If anti-replay has been enabled in the security association, senders
MUST set the Timestamp field to the current time. The format is 64
bits, and the contents are the number of milliseconds since January
1, 1970 00:00 UTC.
If anti-replay has been enabled, receivers MUST be configured with an
allowed Delta value and maintain a cache of messages received within
this time period from each specific source address. Receivers MUST
then check the Timestamp field as follows:
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o A packet with a Timestamp field value beyond the current time plus
or minus the allowed Delta value MUST be silently discarded.
Recommended default value for the allowed Delta is 3,600 seconds.
o A packet accepted according to the above rule MUST be checked for
uniqueness within the cache of received messages from the given
source address. A packet that has already been seen from the same
source with the same Timestamp field value MUST be silently
discard.
o A packet that passes both of the above tests MUST be registered in
the cache for the given source address.
o If the cache becomes full, the receiver SHOULD temporarily reduce
the Delta value for that source address so that all messages
within that value can still be stored.
Note that timestamps are not necessary for replay protection in
solicited advertisements, but must be included in the messages.
7.1.5 Processing Rules for Senders
A node sending a packet using the AH_RSA_Sig transform MUST construct
the packet as follows:
o The Next Header, Payload Len, and Reserved fields are set as
described in RFC 2402.
o The Security Parameters Index is set to the value specified in
Section 7.1.1.
o The Sequence Number field is set to 0.
o The Timestamp field is set as described in Section 7.1.4.
o The Key Information field in the Authentication Data field is set
to the SendKeyInformation structure according to the rules in
Section 7.1.2 and [27]. The used public key is the one stored in
the security association.
o The packet, in the form defined for AH's coverage, is signed using
the private key in the security association, and the resulting
PCKS #1 signature is put to the Digital Signature field. One of
the keys from the Key Information field is used for this purpose,
as described in Section 7.1.2.
o Additionally, if the use of CGA has been specified for the
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security association, the source address of the packet MUST be
constructed as specified in [27].
7.1.6 Processing Rules for Receivers
A packet received on a security association employing AH_RSA_Sig
transform MUST be checked as follows:
o Next Header and Payload Len fields are valid as specified in RFC
2402.
o The SPI field is equal to the value defined in Section 7.1.1.
o The Timestamp field is verified as described in Section 7.1.4.
o The Key Information and Digital Signature fields have correct
encoding, and do not exceed the length of the Authentication Data
field.
o If the use of CGA has been specified in the security association,
we additionally require the receiving node to verify the source
address of the packet using the algorithm described in Section 5
of [27]. The inputs for the algorithm are the contents of the
CGAParameters structure from the Key Information field, the source
address of the packet, and the minimum acceptable Sec value from
the security association. If the CGA verification is successful,
the recipient proceeds with the cryptographically more time
consuming check of the AH signature.
Note that a receiver which does not support CGA or has not
specified its use in its security associations can still verify
packets using trusted roots, even if CGA had been used on a
packet. The CGA property of the address is simply left untested.
o The Digital Signature verification shows that it has been
calculated as specified in the previous sections.
o If the use of a trusted root has been configured for the security
association, a valid authorization delegation chain is known
between the receiver's trusted root and the sender's public key.
Note that the receiver may verify just the CGA property of a
packet, even if the sender has used a trusted root as well.
Packets that do not pass all the above tests MUST be silently
discarded.
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7.2 Other IPsec Extensions
7.2.1 Destination Agnostic Security Associations
In order to allow the same security association to be used when the
the node sends packets to different peers using the same addresses,
an extension must be provided to the RFC 2401 rules on how security
associations are identified. This change is particularly important,
for instance, when routers use the same keys and security association
to send Router Advertisements for up to number of prefixes x 2^64
hosts on an interface.
This extension is mandatory for all nodes that support the AH_RSA_Sig
transform. Security associations that use the SPI value specified in
Section 7.1.1 MUST be identified solely by the SPI and protocol
numbers, not by the destination IP address.
Note that this extension can be supported without implementation
modifications where the proposed revisions of the IPsec standards are
in use [26].
7.2.2 ICMP Type Specific Selectors
In order to allow finer granularity of protection for various ICMPv6
messages, it is necessary to extend the security policy database and
security association selectors with the capability to distinguish
between different messages.
All nodes that support the AH_RSA_Sig transform MUST be capable of
using ICMP and ICMPv6 Type field as a selector.
Note that this can be achieved in an implementation by using the port
number field to contain the ICMP type if the protocol field is ICMP.
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8. Securing Neighbor Discovery with SEND
This section describes how to use IPsec and the mechanisms from [27],
Section 6, Section 7 in order to provide security for Neighbor
Discovery.
8.1 Neighbor Solicitation Messages
All Neighbor Solicitation messages are protected with AH_RSA_Sig.
8.1.1 Sending Secure Neighbor Solicitations
Secure Neighbor Solicitation messages are sent as described in RFC
2461 and 2462, with the additional requirements listed in the
following.
All Neighbor Solicitation messages sent MUST be protected with IPsec,
using the AH_RSA_Sig transform. The security associations used for
this MUST be configured with the sender's key pair, optionally
setting the CGA flag and including additional CGA parameter
information.
The source address of the message MUST NOT be the unspecified
address. A Neighbor Solicitation sent as a part of Duplicate Address
Detection MUST use as a source address the tentative address for
which the Duplicate Address Detection is being run.
In SEND, Neighbor Solicitations MUST be sent either to the target
address or to the securely-solicited-node multicast address
corresponding to the target address. When an interface is
initialized, a node MUST join securely-solicited-node multicast
address corresponding to each of the IP addresses assigned to the
interface. The set of addresses assigned to an interface may change
over time. New addresses might be added and old addresses might be
removed [7]. In such cases the node MUST join and leave the
securely-solicited-node multicast address corresponding to the new
and old addresses, respectively. Note that multiple unicast
addresses may map into the same solicited-node multicast address; a
node MUST NOT leave the securely-solicited-node multicast group until
all assigned addresses corresponding to that multicast address have
been removed.
The Nonce option MUST be included in all messages.
8.1.2 Receiving Secure Neighbor Solicitations
Received Neighbor Solicitation messages are processed as described in
RFC 2461 and 2462, with the additional SEND-related requirements
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listed in the following.
Neighbor Solicitation messages received without an IPsec AH header
and the AH_RSA_Sig transform MUST be silently discarded. The
security associations used for this MUST be configured with the
expected authorization mechanism (CGA or trusted root), the minimum
allowable key size, and optionally with the information related to
the trusted root and the acceptable minSec value.
If source address of the Neighbor Solicitation message is the
unspecified address, the message MUST be silently discarded.
Neighbor Solicitations received without the Nonce option MUST be
silently discarded.
8.2 Neighbor Advertisement Messages
All Neighbor Advertisement messages are protected with AH_RSA_Sig.
8.2.1 Sending Secure Neighbor Advertisements
Secure Neighbor Advertisement messages are sent as described in RFC
2461 and 2462, with the additional requirements listed in the
following.
All Neighbor Advertisement messages sent MUST be protected with
IPsec, using the AH_RSA_Sig transform. The security associations
used for this MUST be configured with the sender's key pair,
optionally setting the CGA flag and including additional CGA
parameter information.
Neighbor Advertisements sent in response to a Neighbor Solicitation
MUST contain a copy of the Nonce option included in the solicitation.
The source address of the message MUST NOT be the unspecified
address.
8.2.2 Receiving Secure Neighbor Advertisements
Received Neighbor Advertisement messages are processed as described
in RFC 2461 and 2462, with the additional SEND-related requirements
listed in the following.
Neighbor Advertisement messages received without an IPsec AH header
and the AH_RSA_Sig transform MUST be silently discarded. The
security associations used for this MUST be configured with the
expected authorization mechanism (CGA or trusted root), the minimum
allowable key size, and optionally with the information related to
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the trusted root and the acceptable minSec value.
Received Neighbor Advertisements sent to a unicast destination
address without a Nonce option MUST be silently discarded.
If source address of the Neighbor Advertisement message is the
unspecified address, the message MUST be silently discarded.
8.3 Other Requirements
Upon receiving a message for which the receiver has no certificate
chain to a trusted root, the receiver MAY use Authorization
Delegation Discovery to learn the certificate chain of the peer.
Hosts that use stateless address autoconfiguration MUST generate a
new CGA as specified in Section 4 of [27] for each new
autoconfiguration run.
It is outside the scope of this specification to describe the use of
trusted root authorization between hosts 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 [9]. If the CGA method is not used, hosts would be required
to exchange certificate chains that terminate in a certificate
authorizing a host 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.
8.4 Configuration
This section shows example security policy and security associations
database entries for the protection of Neighbor Solicitation and
Advertisement messages. The following table summarizes the inbound
security policy data base along with the inbound security
associations:
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Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: NS | * | own | SA = NS_In |
+------------------------------------------------------------------+
| ICMPv6: NS | * | sec-sol-node MC | SA = NS_In |
+------------------------------------------------------------------+
| ICMPv6: NA | * | own | SA = NA_In |
+------------------------------------------------------------------+
| ICMPv6: NA | * | all-nodes MC | SA = NA_In |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| NS_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| NA_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
The following table summarizes outbound security policy database:
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Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: NS | own | * | SA = NS_Out |
+------------------------------------------------------------------+
| ICMPv6: NA | own | * | SA = NA_Out |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| NS_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| NA_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
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9. Securing Router Discovery with SEND
This section describes how to use IPsec and the mechanisms from [27],
Section 6, Section 7 in order to provide security for Router
Discovery.
9.1 Router Solicitation Messages
All Router Solicitation messages are protected with AH_RSA_Sig.
9.1.1 Sending Secure Router Solicitations
Secure Router Solicitation messages are sent as described in RFC
2461, with the additional requirements listed in the following.
All Router Solicitation messages sent MUST be protected with IPsec,
using the AH_RSA_Sig transform. The security associations used for
this MUST be configured with the sender's key pair, optionally
setting the CGA flag and including additional CGA parameter
information.
Hosts SHOULD avoid the use of the unspecified address as the source
address in a Router Solicitation message, if other addresses are
available.
The Nonce option MUST be included in all messages.
9.1.2 Receiving Secure Router Solicitations
Received Router Solicitation messages are processed as described in
RFC 2461, with the additional SEND-related requirements listed in the
following.
Router Solicitation messages received without an IPsec AH header and
the AH_RSA_Sig transform MUST be silently discarded. The security
associations used for this MUST be configured with the expected
authorization mechanism (CGA or trusted root), the minimum allowable
key size, and optionally with the information related to the trusted
root and the acceptable minSec value.
Router Solicitations received without the Nonce option MUST be
silently discarded.
9.2 Router Advertisement Messages
All Router Advertisement messages are protected with AH_RSA_Sig.
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9.2.1 Sending Secure Router Advertisements
Secure Router Advertisement messages are sent as described in RFC
2461, with the additional requirements listed in the following.
All Router Advertisement messages sent MUST be protected with IPsec,
using the AH_RSA_Sig transform. The security associations used for
this MUST be configured with the sender's key pair, optionally
setting the CGA flag and including additional CGA parameter
information.
Router Advertisements sent in response to a Router Solicitation MUST
contain a copy of the Nonce option included in the solicitation.
The source address of the message MUST NOT be the unspecified
address.
9.2.2 Receiving Secure Router Advertisements
Received Router Advertisement messages are processed as described in
RFC 2461, with the additional SEND-related requirements listed in the
following.
Router Advertisement messages received without an IPsec AH header and
the AH_RSA_Sig transform MUST be silently discarded. The security
associations used for this MUST be configured with the expected
authorization mechanism (CGA or trusted root), the minimum allowable
key size, and optionally with the information related to the trusted
root and the acceptable minSec value.
Received Router Advertisements sent to a unicast destination address
without a Nonce option MUST be silently discarded.
If source address of the Router Advertisement message is the
unspecified address, the message MUST be silently discarded.
9.3 Redirect Messages
All Redirect messages are protected with AH_RSA_Sig.
9.3.1 Sending Redirects
Secure Redirect messages are sent as described in RFC 2461, with the
additional requirements listed in the following.
All Redirect messages sent MUST be protected with IPsec, using the
AH_RSA_Sig transform. The security associations used for this MUST
be configured with the sender's key pair, optionally setting the CGA
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flag and including additional CGA parameter information.
The source address of the Redirect message MUST NOT be the
unspecified address.
9.3.2 Receiving Redirects
Received Redirect messages are processed as described in RFC 2461,
with the additional SEND-related requirements listed in the
following.
Redirect messages received without an IPsec AH header and the
AH_RSA_Sig transform MUST be silently discarded. The security
associations used for this MUST be configured with the expected
authorization mechanism (CGA or trusted root), the minimum allowable
key size, and optionally with the information related to the trusted
root and the acceptable minSec value.
If only CGA-based security associations are used, hosts MUST follow
the rules defined below when receiving Redirect messages:
1. The Redirect message MUST be protected as discussed above.
2. The receiver MUST verify that the Redirect message comes from an
IP address to which the host may have earlier sent the packet
that the Redirect message now partially returns. That is, the
source address of the Redirect message must be the default router
for traffic sent to the destination of the returned packet. If
this is not the case, the message MUST be silently discarded.
This step prevents a bogus router from sending a Redirect message
when the host is not using the bogus router as a default router.
If source address of the Redirect message is the unspecified address,
the message MUST be silently discarded.
9.4 Other Requirements
The certificate for a router MAY specify the global IP address(es) of
the router. If so, only these addresses can appear in advertisements
where the Router Address (R) bit [15] is set. All hosts MUST have
the certificate of a trusted root.
Hosts SHOULD use Authorization Delegation Discovery to learn the
certificate chain of their default router or peer host, as explained
in Section 6. The receipt of a protected Router Advertisement
message for which no router Authorization Certificate and certificate
chain is available triggers Authorization Delegation Discovery.
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9.5 Configuration
This section shows example security policy and security associations
database entries for the protection of Redirect, Router Solicitation
and Advertisement messages. The following table summarizes the
inbound security policy data base along with the inbound security
associations:
Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: RS | * | own | SA = RS_In |
+------------------------------------------------------------------+
| ICMPv6: RS | * | all-routers MC | SA = RS_In |
+------------------------------------------------------------------+
| ICMPv6: RA | * | own | SA = RA_In |
+------------------------------------------------------------------+
| ICMPv6: RA | * | all-nodes MC | SA = RA_In |
+------------------------------------------------------------------+
| ICMPv6: REDIRECT | * | own | SA = RE_In |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| RS_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| RA_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| RE_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
The following table summarizes outbound security policy database.
The Router Advertisement and Redirect entries are only present in
routers.
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Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: RS | own | * | SA = RS_Out |
+------------------------------------------------------------------+
| ICMPv6: RA | own | * | SA = RA_Out |
+------------------------------------------------------------------+
| ICMPv6: REDIRECT | own | * | SA = RE_Out |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| RS_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| RA_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| RE_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
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10. Co-Existence of SEND and ND
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. In such a case, the link is required to
operate as two separate logical links, and packets between a secure
and insecure node always go through the router.
Routers configured for SEND advertise two sets of globally routable
prefixes: one set for SEND nodes and one set for nodes that implement
insecure Neighbor Discovery. The insecure nodes will ignore the
advertisements sent using SEND, as the original Neighbor Discovery
specifications require silently discarding packets if they contain an
AH header that they can not verify.
10.1 Behavior Rules
The following considerations apply to all nodes:
o Nodes configured for SEND MUST listen to the solicited-node
multicast address in addition to the securely-solicited-node
multicast address. The messages received on the solicited-node
multicast address are unprotected, but the SEND node MUST respond
to them as follows.
Upon seeing a Neighbor Solicitation for an address which is
currently assigned to its own interface, the SEND node sends as a
response a Neighbor Solicitation with the following contents:
* Source address is the unspecified address.
* Destination address is the solicited-node multicast address of
the target address.
* Target address is copied from the original Neighbor
Solicitation.
* No AH header is included.
* The Nonce option is included in the Neighbor Solicitation.
As a result of seeing this Neighbor Solicitation, the sender of
the original Neighbor Solicitation concludes that it is attempting
to use an address which another node is also attempting to use.
This prevents the non-SEND node from using an address already in
use by a SEND node.
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On some interface types, multicast messages can loop back to the
sending node. In order to prevent the SEND node from responding
to itself, the above solicitations MUST NOT be sent when the
original Neighbor Solicitation included the Nonce option.
Note that while SEND nodes attempt to ensure that non-SEND nodes
use addresses not assigned to the SEND nodes, the reverse is not
true: SEND nodes do not avoid the use of an address which is
already claimed to be in use by a non-SEND node. This is
necessary in order to prevent a denial-of-service attack on secure
Duplicate Address Detection.
o Similarly, when performing Duplicate Address Detection, nodes
configured for SEND MUST send the Neighbor Solicitations both to
the securely-solicited-node multicast address with protection, and
to the solicited-node multicast address without protection.
The following considerations apply to hosts:
o Hosts configured for SEND MUST use SEND for all of their
addresses, including link local addresses.
o Hosts configured for SEND MUST validate all Router Advertisements
with the protocol described in Section 8. Note that this includes
discarding advertisements received without a valid IPsec AH
header, thus making insecure prefixes invisible to them.
o Hosts configured for SEND MUST secure and validate all Neighbor
Advertisements with the protocol described in Section 8. Note
that this includes discarding advertisements received without a
valid IPsec AH header.
The following considerations apply to routers:
o Routers MUST send two sets of Router Advertisements. The
advertisements containing the secure prefixes MUST be secured with
the protocol described in Section 9. The advertisements
containing the insecure prefixes MUST be sent without AH header.
o Routers MUST assign different addresses for their secure and
insecure communications, including their link-local addresses.
Secure Router and Neighbor Advertisements MUST use a source
address that satisfies the security properties outlined in Section
9. Unless this address is link-local, it MUST belong to one of
the advertised secure prefixes. Similarly, source addresses for
insecure advertisements MUST belong to one of the advertised
insecure prefixes, unless the address is link-local.
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o Routers MUST refrain from sending Redirects to a SEND-secured node
with the Destination Address field set to an address for an
insecure node. Similarly, routers MUST refrain from sending
Redirects to a insecure node with the Destination Address field
set to an address for a SEND-secured node
The above rules require secure nodes to ignore all insecure Neighbor
and Router Discovery messages, and all insecure nodes to ignore all
SEND-secured messages. This implies that the secure and insecure
nodes will not be able to discover each other, or even realize that
the other prefixes are on-link. Thus, these hosts will request the
router to route packets destined to a host in the other group. The
rules regarding Redirect messages above have been provided to ensure
that the router performs its routing task and does not instruct the
hosts to communicate directly.
One effect of this is that secure hosts can not communicate with
insecure hosts using link-local addresses, and vice versa.
The security policy or security association database entries are
needed for insecure nodes as far as Neighbor Discovery is concerned.
SEND-secured nodes have the usual entries required by SEND.
10.2 Configuration
This section presents the security policy and security association
data base configuration required for the co-existence of SEND and
non-SEND hosts. The following table summarizes the inbound
configuration on a SEND node:
Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: NS | * | own | SA = NS_In |
+------------------------------------------------------------------+
| ICMPv6: NS | unspecified | solicited-node MC| pass |
+------------------------------------------------------------------+
| ICMPv6: NS | * | sec.sol-node MC | SA = NS_In |
+------------------------------------------------------------------+
| ICMPv6: NA | * | own | SA = NA_In |
+------------------------------------------------------------------+
| ICMPv6: NA | * | all-nodes MC | SA = NA_In |
+------------------------------------------------------------------+
| ICMPv6: RS | * | own | SA = RS_In |
+------------------------------------------------------------------+
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| ICMPv6: RS | * | all-routers MC | SA = RS_In |
+------------------------------------------------------------------+
| ICMPv6: RA | * | own | SA = RA_In |
+------------------------------------------------------------------+
| ICMPv6: RA | * | all-nodes MC | SA = RA_In |
+------------------------------------------------------------------+
| ICMPv6: REDIRECT | * | own | SA = RE_In |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| NS_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| NA_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| RS_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| RA_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
| RE_In | Inbound | To be | AH | AH_RSA_Sig |
| | | assigned | |CGA flag = yes/no|
| | | by IANA | | root = ... (opt)|
+------------------------------------------------------------------+
The second table summarizes the outbound configuration:
Policy entries:
+------------------------------------------------------------------+
| Proto: Type | Source | Destination | Treatment |
+------------------------------------------------------------------+
| ICMPv6: NS | unspecified | solicited-node MC| pass |
+------------------------------------------------------------------+
| ICMPv6: NS | own | * | SA = NS_Out |
+------------------------------------------------------------------+
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| ICMPv6: NA | own | * | SA = NA_Out |
+------------------------------------------------------------------+
| ICMPv6: RS | own | * | SA = RS_Out |
+------------------------------------------------------------------+
| ICMPv6: RA | own | * | SA = RA_Out |
+------------------------------------------------------------------+
| ICMPv6: REDIRECT | own | * | SA = RE_Out |
+------------------------------------------------------------------+
Security associations:
+------------------------------------------------------------------+
| Name | Direction | SPI | Proto | Transform |
+------------------------------------------------------------------+
| NS_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| NA_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| RS_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| RA_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
| RE_Out | Outbound | To be | AH | AH_RSA_Sig |
| | | assigned | | key pair = ... |
| | | by IANA | | CGA = yes/no |
| | | | | CGA params = ...|
| | | | | root = ... (opt)|
+------------------------------------------------------------------+
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11. Performance Considerations
The computations related to AH_RSA_Sig transform are substantially
more expensive than those with traditional symmetric transforms.
While computational power is increasing, it appears still impractical
to use asymmetric transforms for a significant number of packets.
In the application for which AH_RSA_Sig has been designed, however,
hosts typically have the need to perform only a few 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 operations on a
router is on the order of a few dozen operations per second, some of
which can be precomputed as discussed below. A large number of
router solicitations may cause higher demand for performing
asymmetric operations, although RFC 2461 limits the rate at which
responses to solicitations can be sent.
Signatures related to the use of the AH_RSA_Sig transform MAY be
precomputed for Multicast Neighbor and Router Advertisements.
Typically, solicited advertisements are sent to the unicast address
from which the solicitation was sent. Given that the IPv6 header is
covered by the AH integrity protection, it is typically not possible
to precompute solicited advertisements.
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12. Implementation Considerations
In addition to the IPsec extensions discussed in this specification,
it becomes necessary for the IPsec AH implementation and the Neighbor
Discovery implementation to exchange some information. Because IPsec
security associations are typically set up either manually or using
IKE, keys are shared and traditional IPsec does not have to deal with
certificates. SEND uses public key cryptography, however, and
therefore the keys included in the AH header must be certified,
except in the case where simple proof of IP address ownership using
CGAs is being determined. This requires an API between the
AH_RSA_Sig transform processing code and the host's certificate
store, so that the received keys can be checked. Furthermore, if the
necessary certificate chain is not in the certificate store, a
Delegation Chain Solicitation message must be triggered to fetch the
chain. This may require an additional API, although, depending on
how the certificate store is implemented, the API may or may not
involve the code for the AH_RSA_Sig transform.
Both the extensions and the API are required for all types of IPsec
implementations, including Bump-in-the-Stack (BITS) implementations.
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13. Security Considerations
13.1 Threats to the Local Link Not Covered by SEND
SEND does not compensate for an insecure link layer. In particular,
there is 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 with valid AH 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. To protect against such attacks,
link layer security MUST be used. An example of such for 802 type
networks is port-based access control [34].
Prior to participating in Neighbor Discovery and Duplicate Address
Detection, nodes must subscribe to the All Nodes Multicast Group and
Solicited Node Multicast Group for the address that they are claiming
RFC 2461 [6]. Subscribing to a multicast group requires that the
nodes use MLD [22]. 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.
13.2 How SEND Counters Threats to Neighbor Discovery
The SEND protocol is designed to counter the threats to IPv6 Neighbor
Discovery outlined in [28]. The following subsections contain a
regression of the SEND protocol against the threats, to illustrate
what aspects of the protocol counter each threat.
13.2.1 Neighbor Solicitation/Advertisement Spoofing
This threat is defined in Section 4.1.1 of [28]. The threat is that
a spoofed Neighbor Solicitation or Neighbor Advertisement causes 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. There are two cases:
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1. A router receiving a Router Solicitation with a firm IPv6
source address and a Target Link-Layer Address extension
inserts an entry for the IPv6 address into its Neighbor
Cache.
2. A node doing 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.
2. Entries made as a result of a Neighbor Advertisement sent as a
response to a Neighbor Solicitation for purposes of on-link
address resolution.
13.2.1.1 Solicitations with Effect
SEND counters the threat of solicitations with effect in the
following ways:
1. As discussed in Section 5, SEND nodes preferably send Router
Solicitations with a firm IPv6 address and AH header, 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. When SEND nodes are performing DAD, they use the tentative
address as the source address on the Neighbor Solicitation
packet, and include an IPv6 AH header. This allows the receiving
SEND node to verify the solicitation.
See Section 13.2.5, below, for discussion about replay protection and
timestamps.
13.2.1.2 Address Resolution
SEND counters attacks on address resolution by requiring that the
responding node include an AH header with a signature on the packet,
and that the node's interface identifier either be a CGA or that the
node be able to produce a certificate authorizing that node to use
the interface identifier.
The Neighbor Solicitation and Advertisement pairs implement a
challenge-response protocol, as explained in Section 8 and discussed
in Section 13.2.5 below.
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13.2.2 Neighbor Unreachability Detection Failure
This attack is described in Section 4.1.2 of [28]. SEND counters
this attack by requiring a node responding to Neighbor Solicitations
sent as NUD probes to include an AH header 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.
13.2.3 Duplicate Address Detection DoS Attack
This attack is described in Section 4.1.3 of [28]. SEND counters
this attack by requiring the Neighbor Advertisements sent as
responses to DAD to include an AH header 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.
When a SEND node is used on a link that also connects to non-SEND
nodes, the SEND node defends its addresses by sending unprotected
Neighbor Solicitations with an unspecified address, as explained in
Section 10. However, the SEND node ignores any unprotected Neighbor
Solicitations or Advertisements that may be send by the non-SEND
nodes. This protects the SEND node from DAD DoS attacks by non-SEND
nodes or attackers 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 [27].
13.2.4 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 [28]. SEND counters these attacks by requiring Router
Advertisements to contain an AH header, and that the signature in the
header be calculated using the public key of a host that can prove
its authorization to route the subnet prefixes contained in any
Prefix Information Options. The router proves it authorization by
showing an attribute certificate containing the specific prefix or
the indication that the router is allowed to route any prefix. A
Router Advertisement without these protections is dropped as part of
the IPsec processing.
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 [28].
13.2.5 Replay Attacks
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This attack is described in Section 4.3.1 of [28]. 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 into the AH header. 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 7.1.4, this may affect some
nodes.
13.2.6 Neighbor Discovery DoS Attack
This attack is described in Section 4.3.2 of [28]. 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.
13.3 Attacks against SEND Itself
The CGAs have a 59-bit hash value. The security of the CGA mechanism
has been discussed in [27].
Some Denial-of-Service attacks against ND 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.
Security associations based on the use of asymmetric cryptography can
be vulnerable to Denial-of-Service attacks, particularly when the
attacker can guess the SPIs and destination addresses used in the
security associations. In SEND this is easy, as both the SPIs and
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the addresses (such as all nodes multicast address) are standardized.
Due to the use of multicast, one packet sent by the attacker will be
processed by multiple receivers.
When CGA protection is used, SEND deals with these attacks using the
verification process described in Section 7.1.6. In this process a
simple hash verification of the CGA property of the address is
performed first before performing the more expensive signature
verification.
When trusted roots 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 AH_RSA_Sig transform, and start selectively
dropping packets if too many resources are spent. Implementations
MAY also drop first 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
request a large number of delegation chains to be discovered for
different roots. 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
and verification resources for them. Hosts defend against such
attacks by limiting the amount of resources devoted to the
certificate chains and their verification. Hosts SHOULD also
prioritize advertisements sent as a response to their requests above
multicast advertisements.
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14. 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
6.1.
o The Delegation Chain Advertisement message, described in Section
6.2.
This document defines two new Neighbor Discovery [6] options, which
must be assigned Option Type values within the option numbering space
for Neighbor Discovery messages:
o The Trusted Root option, described in Section 6.3.
o The Certificate option, described in Section 6.4.
o The Nonce option, described in Section 5.3.
This document defines a new reserved SPI number in the Reserved SPI
range 1-255 [3].
This document defines a new IPSEC AH Transform Identifier for the
IPsec DOI [4]. This identifier represents the AH_RSA_Sig transform
from Section 7.1.
This document defines a new name space for the Name Type field in the
Trusted Root option. Future values of this field can be allocated
using standards action [5].
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 [5].
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Normative References
[1] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[2] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[3] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[4] Piper, D., "The Internet IP Security Domain of Interpretation
for ISAKMP", RFC 2407, November 1998.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[6] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[7] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[8] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.
[9] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[10] Bassham, L., Polk, W. and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", RFC
3279, April 2002.
[11] 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.
[12] Farrell, S. and R. Housley, "An Internet Attribute Certificate
Profile for Authorization", RFC 3281, April 2002.
[13] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[14] Lynn, C., "X.509 Extensions for IP Addresses and AS
Identifiers", Internet-Draft (expired)
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draft-ietf-pkix-x509-ipaddr-as-extn-00, February 2002.
[15] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in
IPv6", draft-ietf-mobileip-ipv6-22 (work in progress), May
2003.
[16] International Organization for Standardization, "The Directory
- Authentication Framework", ISO Standard X.509, 2000.
[17] RSA Laboratories, "RSA Encryption Standard, Version 1.5", PKCS
1, November 1993.
[18] National Institute of Standards and Technology, "Secure Hash
Standard", FIPS PUB 180-1, April 1995, <http://
www.itl.nist.gov/fipspubs/fip180-1.htm>.
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Informative References
[19] Postel, J., "Internet Control Message Protocol", STD 5, RFC
792, September 1981.
[20] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, RFC
826, November 1982.
[21] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[22] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.
[23] Arkko, J., "Effects of ICMPv6 on IKE and IPsec Policies",
draft-arkko-icmpv6-ike-effects-01 (work in progress), June
2002.
[24] Arkko, J., "Manual SA Configuration for IPv6 Link Local
Messages", draft-arkko-manual-icmpv6-sas-01 (work in progress),
June 2002.
[25] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002.
[26] Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-04 (work in progress), March 2003.
[27] Aura, T., "Cryptographically Generated Addresses (CGA)",
draft-ietf-send-cga-00.txt (work in progress), May 2003.
[28] Nikander, P., "IPv6 Neighbor Discovery trust models and
threats", draft-ietf-send-psreq-00 (work in progress), October
2002.
[29] Montenegro, G. and C. Castelluccia, "SUCV Identifiers and
Addresses", draft-montenegro-sucv-03 (work in progress), July
2002.
[30] O'Shea, G. and M. Roe, "Child-proof Authentication for MIPv6",
Computer Communications Review, April 2001.
[31] Nikander, P., "Denial-of-Service, Address Ownership, and Early
Authentication in the IPv6 World", Proceedings of the Cambridge
Security Protocols Workshop, April 2001.
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[32] Arkko, J., Aura, T., Kempf, J., Mantyla, V., Nikander, P. and
M. Roe, "Securing IPv6 Neighbor Discovery", Wireless Security
Workshop, September 2002.
[33] Montenegro, G. and C. Castelluccia, "Statistically Unique and
Cryptographically Verifiable (SUCV) Identifiers and Addresses",
NDSS, February 2002.
[34] Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access Control",
IEEE Standard 802.1X, September 2001.
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 01803
USA
EMail: sommerfeld@east.sun.com
Brian Zill
Microsoft
USA
EMail: bzill@microsoft.com
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Pekka Nikander
Ericsson
Jorvas 02420
Finland
EMail: Pekka.Nikander@nomadiclab.com
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Appendix A. Contributors
Steven Bellovin was the first to suggest the use of IPsec in this
manner for the protection of Neighbor Discovery. Ran Atkinson and
Brian Weis have in the past experimented with public-key based
variants of AH for other purposes. Vesa-Matti Mantyla was a
co-author of an unpublished draft from which many of the details of
this document have been inherited. The theoretical foundations of
protecting Neighbor Discovery were laid out in a paper [32] where
Tuomas Aura, Vesa-Matti Mantyla, Pekka Nikander, and Mike Roe were
co-authors.
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Appendix B. Acknowledgements
The authors would like to thank Erik Nordmark, Gabriel Montenegro,
Tuomas Aura, Pekka Savola, and Alper Yegin for interesting
discussions in this problem space.
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Appendix C. IPR Considerations
The optional CGA part of SEND uses public keys and hashes to prove
address ownership. Several IPR claims have been made about such
methods.
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