Network Working Group J. Arkko
Internet-Draft Ericsson
Expires: September 18, 2003 V. Devarapalli
Nokia Research Center
F. Dupont
ENST Bretagne
March 20, 2003
Using IPsec to Protect Mobile IPv6 Signaling between Mobile Nodes and
Home Agents
draft-ietf-mobileip-mipv6-ha-ipsec-04.txt
Status of this Memo
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all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on September 18, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
Mobile IPv6 uses IPsec to protect signaling between the home agent
and the mobile node. Mobile IPv6 base document defines the main
requirements these nodes must follow. This document discusses these
requirements in more depth, illustrates the used packet formats,
describes suitable configuration procedures, and shows how
implementations can process the packets in the right order.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Binding Updates and Acknowledgements . . . . . . . . . 8
3.2 Return Routability Signaling . . . . . . . . . . . . . 9
3.3 Prefix Discovery . . . . . . . . . . . . . . . . . . . 10
3.4 Payload Packets . . . . . . . . . . . . . . . . . . . 10
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1 Mandatory Support . . . . . . . . . . . . . . . . . . 12
4.2 Policy Requirements . . . . . . . . . . . . . . . . . 12
4.3 IPsec Protocol Processing . . . . . . . . . . . . . . 14
4.4 Dynamic Keying . . . . . . . . . . . . . . . . . . . . 16
5. Example Configurations . . . . . . . . . . . . . . . . . . . 18
5.1 Format . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2 Manual Configuration . . . . . . . . . . . . . . . . . 19
5.2.1 Binding Updates and Acknowledgements . . . . . . 19
5.2.2 Return Routability Signaling . . . . . . . . . . 20
5.2.3 Prefix Discovery . . . . . . . . . . . . . . . . 21
5.2.4 Payload Packets . . . . . . . . . . . . . . . . 22
5.3 Dynamic Keying . . . . . . . . . . . . . . . . . . . . 24
5.3.1 Binding Updates and Acknowledgements . . . . . . 24
5.3.2 Return Routability Signaling . . . . . . . . . . 25
5.3.3 Prefix Discovery . . . . . . . . . . . . . . . . 26
5.3.4 Payload Packets . . . . . . . . . . . . . . . . 26
6. Processing Steps within a Node . . . . . . . . . . . . . . . 28
6.1 Binding Update to the Home Agent . . . . . . . . . . . 28
6.2 Binding Update from the Mobile Node . . . . . . . . . 29
6.3 Binding Acknowledgement to the Mobile Node . . . . . . 29
6.4 Binding Acknowledgement from the Home Agent . . . . . 30
6.5 Home Test Init to the Home Agent . . . . . . . . . . . 31
6.6 Home Test Init from the Mobile Node . . . . . . . . . 32
6.7 Home Test to the Mobile Node . . . . . . . . . . . . . 32
6.8 Home Test from the Home Agent . . . . . . . . . . . . 33
6.9 Prefix Solicitation Message to the Home Agent . . . . 33
6.10 Prefix Solicitation Message from the Mobile Node . . . 33
6.11 Prefix Advertisement Message to the Mobile Node . . . 33
6.12 Prefix Advertisement Message from the Home Agent . . . 34
6.13 Payload Packet to the Home Agent . . . . . . . . . . . 34
6.14 Payload Packet from the Mobile Node . . . . . . . . . 34
6.15 Payload Packet to the Mobile Node . . . . . . . . . . 34
6.16 Payload Packet from the Home Agent . . . . . . . . . . 34
6.17 Establishing New Security Associations . . . . . . . . 34
6.18 Rekeying Security Associations . . . . . . . . . . . . 35
6.19 Movements and Dynamic Keying . . . . . . . . . . . . . 36
7. Implementation Considerations . . . . . . . . . . . . . . . 38
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 40
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9. Security Considerations . . . . . . . . . . . . . . . . . . 41
Normative References . . . . . . . . . . . . . . . . . . . . 42
Informative References . . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 43
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44
B. Changes from Previous Version . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . 46
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1. Introduction
This document illustrates the use of IPsec in securing control
traffic relating to Mobile IPv6 [8]. In Mobile IPv6, a mobile node
is always expected to be addressable at its home address, whether it
is currently attached to its home link or is away from home. The
"home address" is an IP address assigned to the mobile node within
its home subnet prefix on its home link. While a mobile node is at
home, packets addressed to its home address are routed to the mobile
node's home link.
While a mobile node is attached to some foreign link away from home,
it is also addressable at a care-of addresses. A care-of address is
an IP address associated with a mobile node that has the subnet
prefix of a particular foreign link. The association between a
mobile node's home address and care-of address is known as a
"binding" for the mobile node. While away from home, a mobile node
registers its primary care-of address with a router on its home link,
requesting this router to function as the "home agent" for the mobile
node. The mobile node performs this binding registration by sending
a "Binding Update" message to the home agent. The home agent replies
to the mobile node by returning a "Binding Acknowledgement" message.
Any other nodes communicating with a mobile node are referred to as
"correspondent nodes". Mobile nodes can provide information about
their current location to correspondent nodes, again using Binding
Updates and Acknowledgements. Additionally, a return routability test
is performed between the mobile node, home agent, and the
correspondent node in order to authorize the establishment of the
binding. Packets between the mobile node and the correspondent node
are either tunneled via the home agent, or sent directly if a binding
exists in the correspondent node for the current location of the
mobile node.
Mobile IPv6 tunnels payload packets between the mobile node and the
home agent in both directions. This tunneling uses IPv6
encapsulation [7]. Where these tunnels need to be secured, they are
replaced by IPsec tunnels [2].
Mobile IPv6 also provides support for the reconfiguration of the home
network. Here the home subnet prefixes may change over time. Mobile
nodes can learn new information about home subnet prefixes through
the "prefix discovery" mechanism.
This document discusses security mechanisms for the control traffic
between the mobile node and the home agent. If this traffic is not
protected, mobile nodes and correspondent nodes are vulnerable to
Man-in-the-Middle, Hijacking, Confidentialitypassive
wiretapping, Impersonation, and
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Denial-of-Service attacks. Any third parties are also vulnerable to
Denial-of-Service attacks [explain further]. These threats attacks
are discussed in more
detail in Section 15.1 of the Mobile IPv6 base specification [8].
In order to avoid these attacks, the base specification uses IPsec
[2] to protect control traffic between the home agent and the mobile
node. This control traffic consists of various messages carried by
the Mobility Header protocol in IPv6 [6]. The traffic takes the
following forms:
o Binding Update and Acknowledgement messages exchanged between the
mobile node and the home agent, as described in Sections 10.3.1,
10.3.2, 11.7.1, and 11.7.3 of the base specification [8].
o Return routability messages Home Test Init and Home Test that pass
through the home agent on their way to a correspondent node, as
described in Section 10.4.6 of the base specification [8].
o ICMPv6 messages exchanged between the mobile node and the home
agent for the purposes of prefix discovery, as described in
Sections 10.6 and 11.4 of the base specification [8].
The nodes may also optionally protect payload traffic passing through
the home agent, as described in Section 5.3 of the base specification
[8]. If multicast group membership control protocols or stateful
address autoconfiguration protocols are supported, payload data
protection support is required.
The control traffic between the mobile node and the home agent
requires message authentication, integrity, correct ordering [IPsec does not ensure ordering of traffic; it permits out of order delivery] and
replay protection. [there is later discussion of a requirement to support manual configuration of SAs, but that is inconsistent with use of anti-replay protection, as noted in 2401, 2402, and 2406.] The mobile node and the home agent must have a
security association to protect this traffic. Furthermore, great
care is needed when using IKE [5] to establish security associations
to Mobile IPv6 home agents. The right kind of addresses must be used
for transporting IKE. This is necessary to avoid circular
dependencies in which the use of a Binding Update triggers the need
for an IKE exchange that cannot complete prior to the Binding Update
having been completed.
The mobile IPv6 base document defines the main requirements the
mobile nodes and home agents must follow when securing the above
traffic. This document discusses these requirements in more depth,
illustrates the used packet formats, describes suitable configuration
procedures, and shows how implementations can process the packets in
the right order.
We begin our description by showing the required wire formats for the
protected packets in Section 3. Section 4 describes rules which
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associated Mobile IPv6, IPsec, and IKE implementations must observe.
Section 5 discusses how IPsec can be configured to use either manual
or automatically established security associations. Section 6 shows
examples of how packets are processed within the nodes.
All implementations of Mobile IPv6 mobile node and home agent MUST
support at least the formats described in Section 3 and obey the
rules in Section 4. The configuration and processing sections are
informative, and should only be considered as one possible way of
providing the required functionality.
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2. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
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3. Packet Formats
3.1 Binding Updates and Acknowledgements
When the mobile node is away from its home, the BUs sent by it to the
home agent MUST support at least the following headers in the
following order:
IPv6 header (source = care-of address,
destination = home agent)
Destination Options header
Home Address option (home address)
ESP header [say here that this is transport mode, right?]
Mobility header
Binding Update
Alternate Care-of Address option (care-of address)
Note that the Alternate Care-of Address option is used to ensure that
the care-of address is protected by ESP. The home agent considers
the address within this option as the current care-of address for the
mobile node.
The Binding Acknowledgements sent back to the mobile node when it is
away from home MUST support at least the following headers in the
following order:
IPv6 header (source = home agent,
destination = care-of address)
Routing header (type 2)
home address
ESP header [say here that this is transport mode, right?]
Mobility header
Binding Acknowledgement
When the mobile node is at home, the above rules are different as the
mobile node can use its home address as a source address. This
typically happens for the de-registration Binding Update when the
mobile is returning home. In this situation, the Binding Updates
MUST support at least the following headers in the following order:
IPv6 header (source = home address,
destination = home agent)
ESP header [same questions as above]
Mobility header
Binding Update
The Binding Acknowledgement messages sent to the home address MUST
support at least the following headers in the following order:
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IPv6 header (source = home agent,
destination = home address)
ESP header [as above]
Mobility header
Binding Acknowledgement
3.2 Return Routability Signaling
When the Home Test Init messages tunneled to the home agent are
protected by IPsec, they MUST support at least the following headers
in the following order:
IPv6 header (source = care-of address,
destination = home agent)
ESP header [OK this looks like a legitimate tunnel mode use of ESP]
IPv6 header (source = home address,
destination = correspondent node)
Mobility Header
Home Test Init
This format assumes that the mobile node's current care-of address is
used as one of the gateway addresses in the security association. As
discussed in Section 4.3, this requires the home agent to update the
gateway address when the mobile node moves. Policy entries and
security association selectors stay the same, however, as the inner
packets do not change upon movements.
Similarly, when the Home Test messages tunneled from the home agent
are protected by IPsec, they MUST support at least the following
headers in the following order:
IPv6 header (source = home agent,
destination = care-of address)
ESP header [ibid]
IPv6 header (source = correspondent node,
destination = home address)
Mobility Header
Home Test
The format used to protect return routability packets relies on the
destination of the tunnel packets to change for the mobile node as it
moves. The home agent's address stays the same, but the mobile
node's address changes upon movements, as if the security
association's tunnel gateway address had changed. When the mobile
node adopts a new care-of address, its source address selection rules
will automatically adopt a new source address for outgoing tunnel
packets. (The home agent accepts packets sent like this, as the
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outer source address in tunnel packets is not checked.)
The process is more complicated in the home agent side, as the home
agent has stored the previous care-of address in its Security
Association Database as the gateway address. When IKE is being used,
the mobile node runs it on top of its then current care-of address,
and the resulting tunnel-mode security associations will use the same
addresses as IKE was transported on. In order for the home agent to
be able to tunnel a Home Test message to the mobile node, it uses the
current care-of address as the destination of the tunnel packets, as
if the home agent had modified the gateway address of the security
association used for this protection. This implies that the same
security association can be used in multiple locations, and no new
configuration or IKE rekeying is needed per movement. [some discussion is needed to explain what the SPD at the home agent looks like to accommodate these SAs]
3.3 Prefix Discovery
If IPsec is used to protect prefix discovery, requests for prefixes
from the mobile node to the home agent MUST support at least the
following headers in the following order.
IPv6 header (source = care-of address,
destination = home agent)
Destination Options header
Home Address option (home address)
ESP header
ICMPv6
Mobile Prefix Solicitation
Again if IPsec is used, solicited and unsolicited prefix information
advertisements from the home agent to the mobile node MUST support at
least the following headers in the following order.
IPv6 header (source = home agent,
destination = care-of address)
Routing header (type 2)
home address
ESP header
ICMPv6
Mobile Prefix Advertisement
3.4 Payload Packets
If IPsec is used to protect payload packets tunneled to the home
agent from the mobile node, a similar format is used as in the case
of tunneled Home Test Init messages. However, instead of the
Mobility Header these packets may contain any legal IPv6 protocol(s):
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IPv6 header (source = care-of address,
destination = home agent)
ESP header
IPv6 header (source = home address,
destination = correspondent node)
Any protocol
Similarly, when the payload packets are tunneled from the home agent
to the mobile node with IPsec protection, they MUST support at least
the following headers in the following order:
IPv6 header (source = home agent,
destination = care-of address)
ESP header
IPv6 header (source = correspondent node,
destination = home address)
Any protocol
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4. Requirements
This section describes mandatory rules for all Mobile IPv6 mobile
nodes and home agents. These rules are necessary in order for it to
be possible to enable IPsec communications despite movements,
guarantee sufficient security, and to ensure correct processing order
of packets.
The rules in the following sections apply only to the communications
between home agents and mobile nodes. They should not be taken as
requirements on how IPsec in general is used by mobile nodes.
4.1 Mandatory Support
The following requirements apply to both home agents and mobile
nodes:
o Manual configuration of security associations MUST be supported.
The configuration of the keys is expected to take place
out-of-band, for instance at the time the mobile node is
configured to use its home agent.
o Automatic key management with IKE [5] MAY be supported. Only
IKEv1 is discussed in this document, even if it is expected that
the next version of IKE can also be used and that it offers
several improvements in this specific application.
o IPsec protection for Binding Updates and Acknowledgements between
the mobile node and home agent MUST be supported and MUST be used.
o IPsec protection for the Home Test Init and Home Test messages
tunneled between the mobile node and home agent MUST be supported
and SHOULD be used.
o IPsec protection for the ICMPv6 messages related to prefix
discovery MUST be supported and SHOULD be used.
o IPsec protection of the payload packets tunneled between the
mobile node and home agent MAY be supported and used.
o If multicast group membership control protocols or stateful
address autoconfiguration protocols are supported, payload data
protection MUST be supported for those protocols.
4.2 Policy Requirements
The following requirements apply to both home agents and mobile
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nodes:
o When a packet is matched against IPsec security policy or
selectors of a security association, an address appearing in a
Home Address destination option MUST be considered as the source
address of the packet. [this is not consistent with the processing specified in 2401.]
o Similarly, a home address within a Type 2 Routing header MUST be
considered as the destination address of the packet, when a packet
is matched against IPsec security policy or selectors of a
security association. [again, not consistent with 2401. explain why this does not create security problems re access control for inbound traffic. Will it be necessary for the SPD to somehow specify that this is how the matching should be performed, because the SA is for a mobile peer, or can a peer unilaterally change from where the destination address is selected for access control checks? Do we need a new entry in the SAD for this address value? Also, the earlier diagrams showed a routing header outside of the ESP boundary, which says that if this is a tunnel mode SA, that header would be ignored.]
o When IPsec is used to protect return routability signaling or
payload packets, the security policy database entries SHOULD be
defined specifically for the tunnel interface between the mobile
node and the home agent. That is, the policy entries are not
generally applied on all traffic on the physical interface(s) of
the nodes, but rather only on traffic that enters this tunnel. [not quite sure how to interpret this, but I am glad to see some explicit words about how to manage an SPD for mobility concerns.]
o The authentication of mobile nodes MAY be based either on machine
or user credentials. Note that multi-user operating systems
typically allow all users of a node to use any of the IP addresses
assigned to the node. This limits the capability of the home
agent to restrict the use of a home address to a particular user
in such environment. Where user credentials are applied in a
multi-user environment, the configuration should authorize all
users of the node to control all home addresses assigned to the
node.
o When the mobile node returns home and de-registers with the Home
Agent, the tunnel between the home agent and the mobile node's
care-of address is torn down. The SPD entries, which were used
for protecting tunneled traffic between the mobile node and the
home agent become inactive. [“inactive” is not a concept present in 2401] The corresponding security
associations could be stored [“stored?”]or deleted depending on how they were
created. If the security associations were created dynamically
using IKE, they are automatically deleted when they expire. If
the security associations were created through manual
configuration, they MUST be retained and used later when the
mobile node
moves aways from home again. [no anti-replay
available for manually configured SAs, but this was a requirement stated
earlier] The security
associations protecting Binding Updates and Acknowledgements, and
prefix discovery SHOULD not be deleted as they do not depend on
care-of addresses and can be used again.
The following rules apply to mobile nodes:
o The mobile node MUST use the Home Address destination option in
Binding Updates and Mobile Prefix Solicitations, sent to the home
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agent from a care-of address.
o When the mobile node receives a changed set of prefixes from the
home agent during prefix discovery, there is a need to configure
new security policy entries, and there may be a need to configure
new security associations. It is outside the scope of this
specification to discuss automatic methods for this. [Is it too hard to specify or is the means of specification not needed for interoperability?
The following rules apply to home agents:
o The home agent MUST use the Type 2 Routing header in Binding
Acknowledgements and Mobile Prefix Advertisements sent to the
mobile node, again due to the need to have the home address
visible when the policy checks are made. [see earlier comments re existing 2401 processing description.]
o It is necessary to avoid the possibility that a mobile node could
use its security association to send a Binding Update on behalf of
another mobile node using the same home agent. In order to do
this, the security policy database entries MUST unequivocally
identify a single security association for any given home address
and home agent when manual keying is used. When dynamic keying is
used, the security policy database entries MUST unequivocally
identify the IKE phase 1 credentials which can be used to
authorize the creation of security associations for a particular
home address. How these mappings are maintained is outside the
scope of this specification, but they may be maintained, for
instance, as a locally administered table in the home agent. If
the phase 1 identity is a FQDN, secure forms of DNS may also be
used. [this requires more explanation]
o When the set of prefixes advertised by the home agent changes,
there is a need to configure new security policy entries, and
there may be a need to configure new security associations. It is
outside the scope of this specification to discuss automatic
methods for this, if new home addresses are required. [sounds like too much magic is required here.]
4.3 IPsec Protocol Processing
The following requirements apply to both home agents and mobile
nodes:
o When securing Binding Updates, Binding Acknowledgements, and
prefix discovery, both the mobile nodes and the home agents SHOULD
use the Encapsulating Security Payload (ESP) [4] header in
transport mode and MUST use a non-null payload authentication
algorithm to provide data origin authentication, connectionless
integrity and optional anti-replay protection. Note that
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Authentication Header (AH) [3] is also possible but for brevity is
not discussed in this specification. [“is possible” is not a very useful phrase for s standard. If you want to ensure support for use of AH in this way, say so. At this stage, I would not encourage use of AH.]
Mandatory support for encryption and integrity protection
algorithms is as defined in RFC 2401 [2], RFC 2402 [3], and RFC
2406 [4]. Care is needed when selecting suitable encryption
algorithms for ESP, however. Currently available integrity
protection algorithms are in general considered to be secure. The
encryption algorithm, DES, mandated by the current IPsec standards
is not, however. This is particularly problematic when security
associations are configured manually, as the same key is used for
a long time. [the algorithms are being moved out of these specifications, and being updated.
o Tunnel mode IPsec ESP MUST be supported and SHOULD be used for the
protection of packets belonging to the return routability
procedure. A non-null encryption transform and authentication
algorithm MUST be applied.[why is encryption needed?]
o IPsec AH [3] authenticator calculation MUST be performed as if a
packet with a Type 2 Routing header would have the home address in
the IPv6 destination address field and the care-of address in the
Routing header. Type 2 Routing header should be treated by IPsec
in the same manner as Type 0 Routing header. [I think this is not consistent with 2402.]
o Similarly, the authenticator calculation MUST be performed as if a
packet with a Home Address destination option would have the home
address in the IPv6 source address field and the care-of address
in the destination option. [not consistent with 2402.]
The following rules apply to mobile nodes:
o When ESP is used to protect Binding Updates, there is no
protection for the care-of address which appears in the IPv6
header outside the area protected by ESP. It is important for the
home agent to verify that the care-of address has not been
tampered. As a result, the attacker would have redirected the
mobile node's traffic to another address. In order to prevent
this, Mobile IPv6 implementations MUST use the Alternate Care-of
Address mobility option in registrations sent to the home agent.
(Note that AH protects also the IPv6 header, and some
implementations might avoid the option if they know AH is being
used.)
o When IPsec is used to protect return routability signaling or
payload packets, the mobile node MUST set the source address it
uses for the outgoing tunnel packets to the current primary
care-of address. The mobile node starts to use a new primary
care-of address immediately after sending a Binding Update to the
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home agent to register this new address.
The following rules apply to home agents:
o When IPsec is used to protect return routability signaling or
payload packets, IPsec security associations are needed to provide
this protection. When the care-of address for the mobile node
changes as a result of an accepted Binding Update, special
treatment is needed for the next packets sent using these security
associations. The home agent MUST set the new care-of address as
the destination address of these packets, as if the destination
gateway address in the security association had changed. [seems like this also requires processing not consistent with 2401.]
4.4 Dynamic Keying
The following requirements apply to both home agents and mobile
nodes:
o If replay protection is required, dynamic keying MUST be used.
IPsec can provide replay protection only if dynamic keying is
used. This may not always be possible, and manual keying would be
preferred in some cases. [not very clear direction here.] IPsec also does not guarantee correct
ordering of packets, only that they have not been replayed.
Because of this, sequence numbers within the Mobile IPv6 messages
ensure correct ordering. However, if a home agent reboots and
loses its state regarding the sequence numbers, replay attacks
become possible. [huh? If the home agent reboots, the SAs go away …] The use of a key management mechanism together
with IPsec can be used to prevent such replay attacks. [poor wording of these last two sentences.]
o If IKE version 1 is used with preshared secrets in main mode, it
determines the shared secret to use from the IP address of the
peer. With Mobile IPv6, however, this may be a care-of address
and does not indicate which mobile node attempts to contact the
home agent. Therefore, if preshared secret authentication is used
in IKEv1 between the mobile node and the home agent then
aggressive mode MUST be used. Note also that care needs to be
taken with phase 1 identity selection. Where the ID_IPV6_ADDR
Identity Payloads is used, unambiguous mapping of identities to
keys is not possible. (The next version of IKE may not have these
limitations.) [again, this text leaves me wondering just what the requirements are in the v1 context.]
The following rules apply to mobile nodes:
o Where dynamic keying is used, the key management protocol MUST use
the care-of address as the source address in the protocol
exchanges with the mobile node's home agent. [reconcile with the previous paragraph, and be more explicit re IKE v2]
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o Conversely, the IPsec security associations with the mobile node's
home agent MUST be requested from the key management protocol with
the home address as the mobile node's address. [ibid]
The security associations for protecting Binding Updates and
Acknowledgements are requested for the Mobility header protocol in
transport mode and for specific IP addresses as endpoints. [this does not seem to say anything about the other selectors; if the intent is to not use them for these SAs, say so.]
Similarly, the security associations for protecting prefix
discovery are requested for the ICMPv6 protocol. Security
associations for payload and return routability protection are
requested for a specific tunnel interface and either the payload
protocol or the Mobility header protocol, in tunnel mode. In this
case one
requested endpoint is an IP address and another the
other [?] one is a
wildcard.
o If the mobile node has used IKE v1 to establish security associations
with its home agent, it should follow the procedures discussed in
Section 11.7.1 and 11.7.3 of the (what spec? Why not cite the RFC?) base specification to determine
whether the IKE endpoints can be moved or if rekeying is needed.
The following rules apply to home agents:
o If the home agent has used IKE to establish security associations
with the mobile node, it should follow the procedures discussed in
Section 10.3.1 and 10.3.2 of the (what spec? Why not cite the RFC?) base specification to determine
whether the IKE endpoints can be moved or if rekeying is needed.
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5. Example Configurations
In the following we describe the Security Policy Database (SPD) and
Security Association Database (SAD) entries necessary to protect
Binding Updates and Binding Acknowledgements exchanged between the
mobile node and the home agent. Our examples assume the use of ESP,
but a similar configuration could also be used to protect the
messages with AH.
Section 5.1 introduces the format we use in the description of the
SPD and the SAD. Section 5.2 describes how to configure manually
keyed security associations, and Section 5.3 describes how to use
dynamic keying.
5.1 Format
The format used in the examples is as follows. The SPD description
has the format
<node> "SPD OUT:"
"-" <spdentry>
"-" <spdentry>
...
"-" <spdentry>
<node> "SPD IN:"
"-" <spdentry>
"-" <spdentry>
...
"-" <spdentry>
Where <node> represents the name of the node, and <spdentry> has the
following format:
"IF" <condition> "THEN USE" <sa> |
"IF" <condition> "THEN CREATE" <pattern> |
Where <condition> is an boolean expression about the fields of the
IPv6 packet, <sa> is the name of a security association, and
<pattern> is a specification for a security association to be
negotiated via IKE [5]. The SAD description has the format
<node> "SAD:"
"-" <sadentry>
"-" <sadentry>
...
"-" <sadentry>
[I don’t know where this syntax comes from? It does not seem to map directly to the SPD and SAD discussions in 2401.]
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Where <node> represents the name of the node, and <sadentry> has the
following format:
<sa> "(" <dir> ","
<spi> ","
<destination> ","
<ahesp> ","
<mode> ")" ":"
<selectors>
Where <dir> is "IN" or "OUT", <spi> is the SPI of the security
association, <destination> is its destination, <ahesp> is normally
"ESP" in our case but could also be "AH", <mode> is either "TUNNEL"
or "TRANSPORT", and <selectors> is a boolean expression about the
fields of the IPv6 packet. [this does not match the description of the SAD in 2401; SAD selectors are fields with values, not Booleans indicating whether a given selector is to be examined.,
We will be using an example mobile node in this section with the home
address "home_address_1". The user's identity in this mobile node is
"user_1". The home agent's address is "home_agent_1".
5.2 Manual Configuration
5.2.1 Binding Updates and Acknowledgements
Here are the contents of the SPD and SAD for protecting Binding
Updates and Acknowledgements:
[as noted above, this notation does not match what 2401 says about SPD entries, so it’s not easy (possible?) to determine whether this is consistent with what might be achieved using an implementation that adheres to 2401.]
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mobile node SPD OUT:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH
THEN USE SA1
mobile node SPD IN:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH
THEN USE SA2
mobile node SAD:
- SA1(OUT, spi_a, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = MH
- SA2(IN, spi_b, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = MH
home agent SPD OUT:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH
THEN USE SA2
home agent SPD IN:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH
THEN USE SA1
home agent SAD:
- SA2(OUT, spi_b, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = MH
- SA1(IN, spi_a, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = MH
In the above, "MH" refers to the protocol number for the Mobility
Header [8].
5.2.2 Return Routability Signaling
In the following we describe the necessary SPD and SAD entries to
protect return routability signaling between the mobile node and the
home agent. Note that the rules in the SPD are ordered, and the ones
in the previous section must take precedence over these ones: [ibid]
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mobile node SPD OUT:
- IF interface = tunnel to home_agent_1 &
source = home_address_1 & destination = any &
proto = MH
THEN USE SA3
mobile node SPD IN:
- IF interface = tunnel from home_agent_1 &
source = any & destination = home_address_1 &
proto = MH
THEN USE SA4
mobile node SAD:
- SA3(OUT, spi_c, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = MH
- SA4(IN, spi_d, home_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = MH
home agent SPD OUT:
- IF interface = tunnel to home_address_1 &
source = any & destination = home_address_1 &
proto = MH
THEN USE SA4
home agent SPD IN:
- IF interface = tunnel from home_address_1 &
source = home_address_1 & destination = any &
proto = MH
THEN USE SA3
home agent SAD:
- SA4(OUT, spi_d, home_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = MH
- SA3(IN, spi_c, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = MH
5.2.3 Prefix Discovery
In the following we describe some additional SPD and SAD entries to
protect prefix discovery.[ibid]
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mobile node SPD OUT:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
THEN USE SA5.
mobile node SPD IN:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
THEN USE SA6
mobile node SAD:
- SA5(OUT, spi_e, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
- SA6(IN, spi_f, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
home agent SPD OUT:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
THEN USE SA6
home agent SPD IN:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
THEN USE SA5
home agent SAD:
- SA6(OUT, spi_f, home_address_1, ESP, TRANSPORT):
source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
- SA5(IN, spi_e, home_agent_1, ESP, TRANSPORT):
source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
Note that the SPDs described above protect all ICMPv6 traffic between
the mobile node and the home agent.
5.2.4 Payload Packets
It is also possible to perform some additional, optional, protection
of tunneled payload packets. This protection takes place in a
similar manner to the return routability protection above, but
requires a different value for the protocol field. The necessary SPD
and SAD entries are shown below. It is assumed that the entries for
protecting Binding Updates and Acknowledgements, and the entries to
protect Home Test Init and Home Test messages take precedence over
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these entries. [by “precedence,” do you mean “occur earlier in the SPD? That is the only form of precedence allowed in 2401.]
mobile node SPD OUT:
- IF interface = tunnel to home_agent_1 &
source = home_address_1 & destination = any &
proto = X
THEN USE SA7
mobile node SPD IN:
- IF interface = tunnel from home_agent_1 &
source = any & destination = home_address_1 &
proto = X
THEN USE SA8
mobile node SAD:
- SA7(OUT, spi_g, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = X
- SA8(IN, spi_h, home_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = X
home agent SPD OUT:
- IF interface = tunnel to home_address_1 &
source = any & destination = home_address_1 &
proto = X
THEN USE SA8
home agent SPD IN:
- IF interface = tunnel from home_address_1 &
source = home_address_1 & destination = any &
proto = X
THEN USE SA7
home agent SAD:
- SA8(OUT, spi_h, home_address_1, ESP, TUNNEL):
source = any & destination = home_address_1 & proto = X
- SA7(IN, spi_g, home_agent_1, ESP, TUNNEL):
source = home_address_1 & destination = any & proto = X
If multicast group membership control protocols such as MLDv1 [9] or
MLDv2 [12] need to be protected, these packets may use a link-local
address rather than the home address of the mobile node. In this
case the source and destination can be left as a wildcard and the SPD
entries will work solely based on the used interface and the
protocol, which is ICMPv6 for both MLDv1 and MLDv2. [is this consistent with the new text on multicast SAs in the latest version of AH and ESP?]
Similar problems are encountered when stateful address
autoconfiguration protocols such as DHCPv6 [10] are used. The same
approach is applicable for DHCPv6 as well. DHCPv6 uses the UDP
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protocol.
Support for multiple layers of encapsulation (such as ESP
encapsulated in ESP) is not required by RFC 2401 [2] and is also
otherwise often problematic. It is therefore useful to avoid setting
the protocol X in the above entries to either AH or ESP. [I don’t think 2401 allows wildcard values for SAD entries for the security protocol field, i.e., when an SA is created one must say which security protocol is being used.]
5.3 Dynamic Keying
In this section we show an example configuration that uses IKE to
negotiate security associations.
5.3.1 Binding Updates and Acknowledgements
Here are the contents of the SPD for protecting Binding Updates and
Acknowledgements: [see prior comments re SPD entry notation variance]
mobile node SPD OUT:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH
THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1
mobile node SPD IN:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH
THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1
home agent SPD OUT:
- IF source = home_agent_1 & destination = home_address_1 &
proto = MH
THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1
home agent SPD IN:
- IF source = home_address_1 & destination = home_agent_1 &
proto = MH
THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1
We have omitted details of the proposed transforms in the above, and
all details related to the particular authentication method such as
certificates beyond listing a specific identity that must be used.
We require IKE v1 to be run using the care-of addresses but still
negotiate IPsec SAs that use home addresses. The extra conditions
set by the home agent SPD for the peer phase 1 identity to be
"user_1" must be verified by the home agent. The purpose of the
condition is to ensure that the IKE phase 2 negotiation for a given
user's home address can't be requested by another user. In the
mobile node, we simply set our local identity to be "user_1".
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These checks also imply that the configuration of the home agent is
user-specific: every user or home address requires a specific
configuration entry. It would be possible to alleviate the
configuration tasks by using certificates that have home addresses in
the Subject AltName field. However, it isn't clear if all IKE
implementations allow one address to be used for carrying the IKE
negotiations when another address is mentioned in the used
certificates. In any case, even this approach would have required
user-specific
tasks in the certificate certification authority.
5.3.2 Return Routability Signaling
Protection for the return routability signaling can be configured in
a similar manner as above. [see prior comments re SPD entry notation variance]
mobile node SPD OUT:
- IF interface = tunnel to home_agent_1 &
source = home_address_1 & destination = any &
proto = MH
THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
local phase 1 identity = user_1
mobile node SPD IN:
- IF interface = tunnel from home_agent_1 &
source = any & destination = home_address_1 &
proto = MH
THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
local phase 1 identity = user_1
home agent SPD OUT:
- IF interface = tunnel to home_address_1 &
source = any & destination = home_address_1 &
proto = MH
THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
peer phase 1 identity = user_1
home agent SPD IN:
- IF interface = tunnel from home_address_1 &
source = home_address_1 & destination = any &
proto = MH
THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
peer phase 1 identity = user_1
Here we specified the gateway address for the security association as
the home address for the mobile node. However, as required by
Section 4.3 the packets will actually be sent to the current care-of
address. In order to avoid writing dynamically changing information
to the SPD entries, the above has been written with the home address
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as the gateway.
5.3.3 Prefix Discovery
In the following we describe some additional SPD entries to protect
prefix discovery with IKE. (Note that when actual new prefixes are
discovered, there may be a need to enter new manually configured SPD
entries to specify the authorization policy for the resulting new
home addresses.) [see prior comments re SPD entry notation variance]
mobile node SPD OUT:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1
mobile node SPD IN:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1
home agent SPD OUT:
- IF source = home_agent_1 & destination = home_address_1 &
proto = ICMPv6
THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1
home agent SPD IN:
- IF source = home_address_1 & destination = home_agent_1 &
proto = ICMPv6
THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1
5.3.4 Payload Packets
Protection for the payload packets happens similarly to the
protection of return routability signaling. As in the manually keyed
case, these SPD entries have lower priority [see prior comment about entry precedence in the SPD] than the above ones. [see prior comments re SPD entry notation variance]
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mobile node SPD OUT:
- IF interface = tunnel to home_agent_1 &
source = home_address_1 & destination = any &
proto = X
THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
local phase 1 identity = user_1
mobile node SPD IN:
- IF interface = tunnel from home_agent_1 &
source = any & destination = home_address_1 &
proto = X
THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
local phase 1 identity = user_1
home agent SPD OUT:
- IF interface = tunnel to home_address_1 &
source = any & destination = home_address_1 &
proto = X
THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
peer phase 1 identity = user_1
home agent SPD IN:
- IF interface = tunnel from home_address_1 &
source = home_address_1 & destination = any &
proto = X
THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
peer phase 1 identity = user_1
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6. Processing Steps within a Node
6.1 Binding Update to the Home Agent
Step 1. At the mobile node, Mobile IPv6 module first produces the
following packet:
IPv6 header (source = home address,
destination = home agent)
Mobility header
Binding Update
Step 2. This packet is matched against the IPsec policy
data baseSPD on
the mobile node and we make a note that IPsec must be applied.
Step 3. Then, we add the necessary Mobile IPv6 options but do not
change the addresses yet, as described in Section 11.2.2 of the base
specification [8]. This results in:
IPv6 header (source = home address,
destination = home agent)
Destination Options header
Home Address option (care-of address)
Mobility header
Binding Update
Step 4. Finally, IPsec headers are added and the necessary
authenticator values are calculated:
IPv6 header (source = home address,
destination = home agent)
Destination Options header
Home Address option (care-of address)
ESP header (SPI = spi_a) [what was the SA created that yielded this SPI?]
Mobility header
Binding Update
Step 5. Before sending the packet, the addresses in the IPv6 header
and the Destination Options header are changed:
IPv6 header (source = care-of address,
destination = home agent)
Destination Options header
Home Address option (home address)
ESP header (SPI = spi_a) [ibid]
Mobility header
Binding Update
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6.2 Binding Update from the Mobile Node
Step 1. The following packet is received at the home agent:
IPv6 header (source = care-of address,
destination = home agent)
Destination Options header
Home Address option (home address)
ESP header (SPI = spi_a) [ibid]
Mobility header
Binding Update
Step 2. The home address option is processed first, which results in
IPv6 header (source = home address,
destination = home agent)
Destination Options header
Home Address option (care-of address)
ESP header (SPI = spi_a) [ibid]
Mobility header
Binding Update
Step 3. ESP header is processed next, resulting in
IPv6 header (source = home address,
destination = home agent)
Destination Options header
Home Address option (care-of address)
Mobility header
Binding Update
Step 4. This packet matches the security association selectors
(source = home address, destination = home agent, proto = MH).
Step 5. Mobile IPv6 processes the Binding Update. The Binding
Update is delivered to the Mobile IPv6 module.
6.3 Binding Acknowledgement to the Mobile Node
Step 1. Mobile IPv6 produces the following packet:
IPv6 header (source = home agent,
destination = home address)
Mobility header
Binding Acknowledgement
Step 2. This packet matches the IPsec policy entries, and we
remember that IPsec has to be applied.
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Step 3. Then, we add the necessary Route Headers but do not change
the addresses yet, as described in Section 9.6 of the base
specification [8]. This results in:
IPv6 header (source = home agent,
destination = home address)
Routing header (type 2)
care-of address
Mobility header
Binding Acknowledgement
Step 4. We apply IPsec:
IPv6 header (source = home agent,
destination = home address)
Routing header (type 2)
care-of address
ESP header (SPI = spi_b)
Mobility header
Binding Acknowledgement
Step 5. Finally, before sending the packet out we change the
addresses in the IPv6 header and the Route header:
IPv6 header (source = home agent,
destination = care-of address)
Routing header (type 2)
home address
ESP header (SPI = spi_b)
Mobility header
Binding Acknowledgement
6.4 Binding Acknowledgement from the Home Agent
Step 1. The following packet is received at the mobile node
IPv6 header (source = home agent,
destination = care-of address)
Routing header (type 2)
home address
ESP header (SPI = spi_b)
Mobility header
Binding Acknowledgement
Step 2. After the routing header is processed the packet becomes
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IPv6 header (source = home agent,
destination = home address)
Routing header (type 2)
care-of address
ESP header (SPI = spi_b)
Mobility header
Binding Acknowledgement
Step 3. ESP header is processed next, resulting in:
IPv6 header (source = home agent,
destination = home address)
Routing header (type 2)
care-of address
Mobility header
Binding Acknowledgement
Step 4. This packet matches the security association selectors
(source = home agent, destination = home address, proto = MH).
Step 5. The Binding Acknowledgement is delivered to the Mobile IPv6
module.
6.5 Home Test Init to the Home Agent
Step 1. The mobile node constructs a Home Test Init message:
IPv6 header (source = home address,
destination = correspondent node)
Mobility header
Home Test Init
Step 2. Mobile IPv6 determines that this packet should go to the
tunnel to the home agent.
Step 3. The packet is matched against IPsec policy entries for the
interface, and we find that IPsec needs to be applied.
Step 4. IPsec tunnel mode headers are added. Note that we use a
care-of address as a source address for the tunnel packet.
IPv6 header (source = care-of address,
destination = home agent)
ESP header (SPI = spi_c)
IPv6 header (source = home address,
destination = correspondent node)
Mobility header
Home Test Init
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Step 5. The packet no longer satisfies the criteria that made it
enter the tunnel, and it is sent directly to the home agent.
6.6 Home Test Init from the Mobile Node
Step 1. The home agent receives the following packet:
IPv6 header (source = care-of address,
destination = home agent)
ESP header (SPI = spi_c)
IPv6 header (source = home address,
destination = correspondent node)
Mobility Header
Home Test Init
Step 2. IPsec processing is performed, resulting in:
IPv6 header (source = home address,
destination = correspondent node)
Mobility Header
Home Test Init
Step 3. The resulting packet matches the selectors and the packet
can be processed further.
Step 4. The packet is then forwarded to the correspondent node.
6.7 Home Test to the Mobile Node
Step 1. The home agent receives a Home Test packet from the
correspondent node:
IPv6 header (source = correspondent node,
destination = home address)
Mobility Header
Home Test Init
Step 2. The home agent determines that this packet is destined to a
mobile node that is away from home, and decides to tunnel it.
Step 3. The packet matches the IPsec policy entries for the tunnel
interface, and we note that IPsec needs to be applied.
Step 4. IPsec is applied, resulting in a new packet. Note that the
home agent must keep track of the location of the mobile node, and
update the tunnel gateway address in the security association(s)
accordingly.
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IPv6 header (source = home agent,
destination = care-of address)
ESP header (SPI = spi_d)
IPv6 header (source = correspondent node,
destination = home address)
Mobility Header
Home Test Init
Step 5. The packet no longer satisfies the criteria that made it
enter the tunnel, and it is sent directly to the care-of address.
6.8 Home Test from the Home Agent
Step 1. The mobile node receives the following packet:
IPv6 header (source = home agent,
destination = care-of address)
ESP header (SPI = spi_d)
IPv6 header (source = correspondent node,
destination = home address)
Mobility Header
Home Test Init
Step 2. IPsec is processed, resulting in:
IPv6 header (source = correspondent node,
destination = home address)
Mobility Header
Home Test Init
Step 3. This matches the security association selectors (source =
any, destination = home address).
Step 4. The packet is given to Mobile IPv6 processing.
6.9 Prefix Solicitation Message to the Home Agent
This procedure is similar to the one presented in Section 6.1.
6.10 Prefix Solicitation Message from the Mobile Node
This procedure is similar to the one presented in Section 6.2.
6.11 Prefix Advertisement Message to the Mobile Node
This procedure is similar to the one presented in Section 6.3.
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6.12 Prefix Advertisement Message from the Home Agent
This procedure is similar to the one presented in Section 6.4.
6.13 Payload Packet to the Home Agent
This procedure is similar to the one presented in Section 6.5.
6.14 Payload Packet from the Mobile Node
This procedure is similar to the one presented in Section 6.6.
6.15 Payload Packet to the Mobile Node
This procedure is similar to the one presented in Section 6.7.
6.16 Payload Packet from the Home Agent
This procedure is similar to the one presented in Section 6.8.
6.17 Establishing New Security Associations
Step 1. The mobile node wishes to send a Binding Update to the home
agent.
IPv6 header (source = home address,
destination = home agent)
Mobility header
Binding Update
Step 2. There is no existing security association to protect the
Binding Update, so IKE is initiated. The IKE packets are sent as
shown in the following examples. The first packet is an example of
an IKE packet sent from the mobile node, and the second one is from
the home agent. The examples shows also that the phase 1 identity
used for the mobile node is a FQDN.
IPv6 header (source = care-of address,
destination = home agent)
UDP
IKE
... IDii = ID_FQDN mn123.ha.net ...
IPv6 header (source = home agent
destination = care-of address)
UDP
IKE
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... IDir = ID_FQDN ha.net ...
Step 3. IKE phase 1 completes, and phase 2 is initiated to request
security associations for protecting traffic between the mobile
node's home address and the home agent. This involves sending and
receiving additional IKE packets. The below example shows again one
packet sent by the mobile node and another sent by the home agent.
The example shows also that the phase 2 identity used for the mobile
node is the mobile node's home address.
IPv6 header (source = care-of address,
destination = home agent)
UDP
IKE
... IDci = ID_IPV6_ADDR home address ...
IPv6 header (source = home agent,
destination = care-of address)
UDP
IKE
... IDcr = ID_IPV6_ADDR home agent ...
Step 4. The remaining steps are as shown in Section 6.1.
6.18 Rekeying Security Associations
Step 1. The mobile node and the home agent have existing security
associations. Either side may decide at any time that the security
associations need to be rekeyed, for instance, because the specified
lifetime is approaching.
Step 2. Mobility header packets sent during rekey may be protected
by the existing security associations.
Step 3. When the rekeying is finished, new security associations are
established. In practice there is a time interval during which an
old, about-to-expire security association and newly established
security association will both exist. The new ones should be used as
soon as they become available.
Step 4. A notification of the deletion of the old security
associations is received. After this, only the new security
associations can be used.
Note that there is no requirement that the existence of the IPsec and
IKE security associations is tied to the existence of bindings. It
is not necessary to delete a security association if a binding is
removed, as a new binding may soon be established after this.
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Since cryptographic acceleration hardware may only be able to handle
a limited number of active security associations, security
associations may be deleted via IKE in order to keep the number of
active cryptographic contexts to a minimum. Such deletions should
not be interpreted as a sign of losing a contact to the peer or as a
reason to remove a binding. Rather, if additional traffic needs to
be sent, it is preferable to bring up another security association to
protect it.
6.19 Movements and Dynamic Keying
In this section we describe the sequence of events that relate to
movement with IKE-based security associations. In the initial state,
the mobile node is not registered in any location and has no security
associations with the home agent. Depending on whether the peers
will be able to move IKE endpoints to new care-of addresses, the
actions taken in Step 9 and 10 are different.
Step 1. Mobile node with the home address A moves to care-of address
B.
Step 2. Mobile node runs IKE from care-of address B to the home
agent, establishing a phase 1.
Step 3. Protected by this phase 1, mobile node establishes a pair of
security associations for protecting Mobility Header traffic to and
from the home address A.
Step 4. Mobile node sends a Binding Update and receives a Binding
Acknowledgement using the security associations created in Step 3.
Step 5. Mobile node establishes a pair of security associations for
protecting return routability packets. These security associations
are in tunnel mode and their endpoint in the mobile node side is
care-of address B. For the purposes of our example, this step uses
the phase 1 connection established in Step 2. Multiple phase 1
connections are also possible.
Step 6. The mobile node uses the security associations created in
Step 5 to run return routability.
Step 7. The mobile node moves to a new location and adopts a new
care-of address C.
Step 8. Mobile node sends a Binding Update and receives a Binding
Acknowledgement using the security associations created in Step 3.
The home agent ensures that the next packets sent using the security
associations created in Step 5 will have the new care-of address as
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their destination address, as if the destination gateway address in
the security association had changed.
Step 9. If the mobile node and the HA have the capability to change
the IKE endpoints, they change the address to C. If they dont have
the capability, both nodes remove their phase 1 connections created
on top of the care-of address B and establish a new IKE phase 1 on
top of the care-of address C. This capability to change the IKE
phase 1 end points is indicated through setting the Key Management
Mobility Capability (K) flag [8] in the Binding Update and Binding
Acknowledgement messages.
Step 10. If a new IKE phase 1 connection was setup after movement,
the MN will not be able to receive any notifications delivered on top
of the old IKE phase 1 security association. Notifications delivered
on top of the new security association are received and processed
normally. If the mobile node and HA were able to update the IKE
endpoints, they can continue using the same IKE phase 1 connection.
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7. Implementation Considerations
We have chosen to require an encapsulation format for return
routability and payload packet protection which can only be realized
if the destination of the IPsec packets sent from the home agent can
be changed as the mobile node moves. One of the main reasons for
choosing such a format is that it removes the overhead of twenty four
bytes when a home address option or routing header is added to the
tunneled packet. What is needed is that the home agent must act as
if the gateway address of a security association to the mobile node
would have changed. Implementations are free to choose any
particular method to make this change, such as using an API to the
IPsec implementation to change the parameters of the security
association, removing the security association and installing a new
one, or modification of the packet after it has gone through IPsec
processing. The only requirement is that after registering a new
binding at the home agent, the next IPsec packets sent on this
security association will be addressed to the new care-of address.
We have also chosen to require that a dynamic key management protocol
must be able to make an authorization decision for IPsec security
association creation with different addresses than with what the key
management protocol is run. We expect this to be done typically by
configuring the allowed combinations of phase 1 user identities and
home addresses.
The base Mobile IPv6 specification sets high requirements for a
so-called Bump-In-The-Stack (BITS) implementation model of IPsec. As
Mobile IPv6 specific modifications of the packets are required after
IPsec processing, the BITS implementation has to perform also some
tasks related to mobility. This may increase the complexity of the
implementation, even if it already performs some tasks of the IP
layer (such as fragmentation).
We have chosen to require policy entries that are specific to a
tunnel interface. This means that implementations have to regard the
Home Agent - Mobile Node tunnel as a separate interface on which
IPsec SPDs can be based.
A further complication of the IPsec processing on a tunnel interface
is that this requires access to the BITS implementation before the
packet actually goes out.
When certificate authentication is used, IKE fragmentation can be
encountered. This can occur when certificate chains are used, or
even with single certificates if they are large. Many firewalls do
not handle fragments properly, and may drop them. Routers in the
path may also discard fragments after the initial one, since they
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typically will not contain full IP headers that can be compared
against an access list. Where fragmentation occurs, the endpoints
will not always be able to establish a security association.
Fortunately, typical Mobile IPv6 deployment uses short certificate
chains, as the mobile node is communicating directly with its home
network. Nevertheless, where the problem appears, one solution is to
replace the firewalls or routers with equipment that can properly
support fragments. If this cannot be done, it may help to store the
peer certificates locally, or to obtain them through other means.
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8. IANA Considerations
No IANA actions are necessary based on this document. IANA actions
for the Mobile IPv6 protocol itself have been covered in [8].
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9. Security Considerations
The Mobile IPv6 base specification [8] requires strong security
between the mobile node and the home agent. This memo discusses how
that security can be arranged in practice, using IPsec.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[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] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[5] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[7] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6
Specification", RFC 2473, December 1998.
[8] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in
IPv6", draft-ietf-mobileip-ipv6-21 (work in progress), February
2003.
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Informative References
[9] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.
[10] Droms, R., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
November 2002.
[11] Kivinen, T., Huttunen, A., Swander, B. and V. Volpe,
"Negotiation of NAT-Traversal in the IKE",
draft-ietf-ipsec-nat-t-ike-04 (work in progress), November
2002.
[12] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
(MLDv2) for IPv6", draft-vida-mld-v2-06 (work in progress),
December 2002.
Authors' Addresses
Jari Arkko
Ericsson
Jorvas 02420
Finland
EMail: jari.arkko@ericsson.com
Vijay Devarapalli
Nokia Research Center
313 Fairchild Drive
Mountain View CA 94043
USA
EMail: vijayd@iprg.nokia.com
Francis Dupont
ENST Bretagne
Campus de Rennes 2, rue de la Chataigneraie
BP 78
Cesson-Sevigne Cedex 35512
France
EMail: Francis.Dupont@enst-bretagne.fr
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Appendix A. Acknowledgements
The authors would like to thank Greg O'Shea, Michael Thomas, Kevin
Miles, Cheryl Madson, Bernard Aboba, Erik Nordmark, and Gabriel
Montenegro for interesting discussions in this problem space.
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Appendix B. Changes from Previous Version
The following changes have been made to this document from version
02:
o The wire format for de-registration when returning home has been
updated. The Alternate Care-of Address option is no longer used
in this situation (tracked issue 270).
o An IANA considerations section has been added (tracked issue 265).
o IPsec protocol and mode requirements have now been stated as
minimal requirements and no longer prevent the use of other
protocols (AH) and modes (tracked issue 228).
o Some editorial modifications have been performed.
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