Network Working Group P. Eronen
Internet-Draft Nokia
Intended status: Standards Track J. Laganier
Expires: May 22, 2009 DOCOMO Euro-Labs
C. Madson
Cisco Systems
November 18, 2008
IPv6 Configuration in IKEv2
draft-ietf-ipsecme-ikev2-ipv6-config-00
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Abstract
When IKEv2 is used for remote VPN access (client to VPN gateway), the
gateway assigns the client an IP address from the internal network
using IKEv2 configuration payloads. The configuration payloads
specified in RFC 4306 work well for IPv4, but make it difficult to
use certain features of IPv6. This document describes the
limitations of current IKEv2 configuration payloads for IPv6, and
explores possible solutions that would allow IKEv2 to set up full-
featured virtual IPv6 interfaces.
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Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Current Limitations . . . . . . . . . . . . . . . . . . . . . 7
3.1. Multiple Prefixes . . . . . . . . . . . . . . . . . . . . 7
3.2. Link-Local Addresses . . . . . . . . . . . . . . . . . . . 7
3.3. Receiving Multicast Traffic . . . . . . . . . . . . . . . 7
3.4. Interface Identifier Selection . . . . . . . . . . . . . . 7
3.5. Sharing VPN Access . . . . . . . . . . . . . . . . . . . . 8
3.6. Additional Information . . . . . . . . . . . . . . . . . . 8
4. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Main Requirements . . . . . . . . . . . . . . . . . . . . 9
4.2. Desirable Non-Functional Properties . . . . . . . . . . . 10
4.3. Implementation Considerations . . . . . . . . . . . . . . 10
4.4. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Solution Discussion . . . . . . . . . . . . . . . . . . . . . 11
5.1. Link Model . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Distributing Prefix Information . . . . . . . . . . . . . 12
5.3. Unique Address Allocation . . . . . . . . . . . . . . . . 13
5.4. Layer 3 Access Control . . . . . . . . . . . . . . . . . . 13
5.5. Other Considerations . . . . . . . . . . . . . . . . . . . 14
6. Solution Sketch . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Initial Exchanges . . . . . . . . . . . . . . . . . . . . 16
6.2. Reauthentication . . . . . . . . . . . . . . . . . . . . . 18
6.3. Creating CHILD_SAs . . . . . . . . . . . . . . . . . . . . 18
6.4. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 18
6.5. Relationship to Neighbor Discovery . . . . . . . . . . . . 19
6.6. Relationship to Existing IKEv2 Payloads . . . . . . . . . 19
7. Payload Formats . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. INTERNAL_IP6_LINK Configuration Attribute . . . . . . . . 21
7.2. INTERNAL_IP6_PREFIX Configuration Attribute . . . . . . . 21
7.3. LINK_ID Notify Payload . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Alternative Solution Sketches . . . . . . . . . . . . 29
A.1. Version -00 Sketch . . . . . . . . . . . . . . . . . . . . 29
A.2. Router Aggregation Sketch #1 . . . . . . . . . . . . . . . 30
A.3. Router Aggregation Sketch #2 . . . . . . . . . . . . . . . 31
A.4. IPv4-like Sketch . . . . . . . . . . . . . . . . . . . . . 33
A.5. Sketch Based on RFC 3456 . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
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1. Introduction and Problem Statement
In typical remote access VPN use (client to VPN gateway), the client
needs an IP address in the network protected by the security gateway.
IKEv2 includes a feature called "configuration payloads" that allows
the gateway to dynamically assign a temporary address to the client
[IKEv2].
For IPv4, the message exchange would look as follows:
Client Gateway
-------- ---------
HDR(IKE_SA_INIT), SAi1, KEi, Ni -->
<-- HDR(IKE_SA_INIT), SAr1, KEr, Nr, [CERTREQ]
HDR(IKE_AUTH),
SK { IDi, CERT, [CERTREQ], AUTH, [IDr],
CP(CFG_REQUEST) =
{ INTERNAL_IP4_ADDRESS(),
INTERNAL_IP4_DNS() }, SAi2,
TSi = (0, 0-65535, 0.0.0.0-255.255.255.255),
TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) } -->
<-- HDR(IKE_AUTH),
SK { IDr, CERT, AUTH,
CP(CFG_REPLY) =
{ INTERNAL_IP4_ADDRESS(192.0.2.234),
INTERNAL_IP4_DNS(10.11.22.33) },
SAr2,
TSi = (0, 0-65535, 192.0.2.234-192.0.2.234),
TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) }
Figure 1: IPv4 configuration
The IPv4 case has been implemented by various vendors, and in general
works well. IKEv2 also defines almost identical configuration
payloads for IPv6:
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Client Gateway
-------- ---------
HDR(IKE_AUTH),
SK { IDi, CERT, [CERTREQ], AUTH, [IDr],
CP(CFG_REQUEST) =
{ INTERNAL_IP6_ADDRESS(),
INTERNAL_IP6_DNS() }, SAi2,
TSi = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF),
TSr = (0,
0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) } -->
<-- HDR(IKE_AUTH),
SK { IDr, CERT, AUTH,
CP(CFG_REPLY) =
{ INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5,
64),
INTERNAL_IP6_DNS(2001:DB8:9:8:7:6:5:4) },
SAr2,
TSi = (0, 0-65535,
2001:DB8:0:1:2:3:4:5 -
2001:DB8:0:1:2:3:4:5),
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0: -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) }
Figure 2: IPv6 configuration
In other words, IPv6 is basically treated as IPv4 with larger
addresses. As noted in [RFC4718], this does not fully follow the
"normal IPv6 way of doing things". The IPsec tunnels are not full-
featured "interfaces" in the IPv6 addressing architecture [IPv6Addr]
sense. For example, they do not necessarily have link-local
addresses, and this may complicate the use of protocols that assume
them.
This document describes what exactly are the limitations of current
IKEv2 configuration payloads for IPv6, and explores possible
solutions that would allow IKEv2-based VPNs to set up full-featured
virtual IPv6 interfaces.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
When messages containing IKEv2 payloads are described, optional
payloads are shown in brackets (for instance, "[FOO]"), and a plus
sign indicates that a payload can be repeated one or more times (for
instance, "FOO+").
This document uses the term "virtual interface" when describing how
the client uses the IPv6 address(es) assigned by the gateway. While
existing IPsec documents do not use this term, it is not a new
concept. In order to use the address assigned by the VPN gateway,
current VPN clients already create a local "virtual interface" (as
only addresses assigned to interfaces can be used, e.g., as source
addresses for TCP connections). Note that this definition of
"interface" is not necessarily identical with what some particular
implementation calls "interface".
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3. Current Limitations
This section explores the limitations of the current IPv6
configuration mechanism.
The IKEv2 specification does not always fully describe the semantics
associated with configuration payloads, only their on-the-wire
format. This section assumes the semantics implied by Figure 2. It
is possible that many of the limitations described here could be
solved by specifying additional semantics for these configuration
payloads.
3.1. Multiple Prefixes
In Figure 2 only a single IPv6 address (from a single prefix) is
assigned. The specification does allow the client to include
multiple INTERNAL_IP6_ADDRESS attributes in its request, but the
gateway cannot assign more addresses than the client requested.
Multiple prefixes are useful for site renumbering, host-based site
multihoming [SHIM6], and unique local IPv6 addresses [RFC4193]. In
all of these cases, the gateway has better information on how many
different addresses (from different prefixes) the client should be
assigned.
3.2. Link-Local Addresses
The IPv6 addressing architecture [IPv6Addr] specifies that "IPv6
addresses of all types are assigned to interfaces, not nodes. [..]
All interfaces are required to have at least one Link-Local unicast
address".
Currently, the virtual interface created by IKEv2 configuration
payloads does not have link-local addresses. This violates
[IPv6Addr] and prevents the use of protocols that require link-local
addresses, such as [MLDv2] and [DHCPv6]
3.3. Receiving Multicast Traffic
Even if MLD would work, the traffic selectors negotiated in Figure 2
do not allow receiving multicast traffic.
3.4. Interface Identifier Selection
In the message exchange shown in Figure 2, the gateway chooses the
interface ID used by the client. It is also possible for the client
to request a specific interface ID; the gateway then chooses the
prefix part.
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This approach complicates the use of Cryptographically Generates
Addresses [CGA]. With CGAs, the interface ID cannot be calculated
before the prefix is known. The client could first obtain a non-CGA
address to determine the prefix, and then send a separate CFG_REQUEST
to obtain a CGA address with the same prefix. However, this approach
requires that the IKEv2 software component provides an interface to
the component managing CGAs; an ugly implementation dependency that
would be best avoided.
Similar concerns apply to other cases where the client has some
interest in what interface ID is being used, such as Hash-Based
Addresses [HBA] and privacy addresses [RFC4941].
Without CGAs and HBAs, VPN clients are not able to fully use IPv6
features such as [SHIM6] or enhanced Mobile IPv6 route optimization
[RFC4866].
3.5. Sharing VPN Access
Some VPN clients may want to share the VPN connection with other
devices (e.g., from a cell phone to a laptop, or vice versa) via some
local area network connection (such as Wireless LAN or Bluetooth).
It is to be determined how common this use case would actually be;
e.g., how likely it is that security policies would allow this.
Quite obviously sharing of VPN access requires more than one address
(unless NAT is used). However, the current model where each address
is requested separately is probably complex to integrate with a local
area network that uses stateless address autoconfiguration. Thus,
obtaining a whole prefix for the VPN client, and advertising that to
the local link (something resembling [NDProxy]) would be preferable.
With DHCPv6 prefix delegation [RFC3633], even [NDProxy] and
associated multi-link subnet issues would be avoided.
3.6. Additional Information
The original 3GPP standards for IPv6 assigned a single IPv6 address
to each mobile phone, resembling current IKEv2 payloads. [RFC3314]
describes the problems with this approach, and caused 3GPP to change
the specifications to assign unique /64 prefix(es) for each phone.
If the VPN client is assigned IPv6 address(es) from prefix(es) that
are shared with other VPN clients, this results in some kind of
multi-link subnet. [Multilink] describes issues associated with
multi-link subnets, and recommends that they should be avoided.
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4. Design Goals
4.1. Main Requirements
o A VPN client can obtain several addresses from a given prefix; the
interface IDs can be selected by the client, and may depend on the
prefix.
o A VPN client can be assigned multiple prefixes for use on the
client-gateway link. The client does not have to know beforehand
how many prefixes are needed.
o The solution should avoid periodic messages over the VPN tunnel.
o The solution should avoid Duplicate Address Detection (DAD) over
the VPN tunnel.
o Multicast works. That is, the client is able to send multicast
packets (tunneled to the gateway via unicast), join multicast
groups using [MLDv2], and receive multicast packets (tunneled from
the gateway to the client via unicast).
o It should be possible to share the VPN access over a local area
network connection, without requiring anything special from other
hosts in the local network (beyond minimal IPv6 node requirements
specified in [RFC4294]).
o Re-authentication works: the client can start a new IKE SA and
continue using the same "virtual link" (with same addresses,
etc.).
o Compatibility with other IPsec uses: Configuring a virtual IPv6
link should not prevent the peers from using IPsec/IKEv2 for other
uses.
o Compatibility with current IPv6 configuration: Although the
current IPv6 mechanism is not widely implemented, new solutions
should not preclude its use (e.g., by defining incompatible
semantics for the existing payloads).
o Compatibility with current IPv4 configuration: it should be
possible to use the existing IPv4 configuration mechanism within
the same IKE SA.
o (Optional/To be determined) When the client is also a router (to
some local network), it should be able to use DHCPv6 prefix
delegation [RFC3633] over the virtual link.
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4.2. Desirable Non-Functional Properties
Note that the following desirable properties may be somewhat
conflicting.
o Re-use existing mechanisms, such as [AUTOCONF] and [DHCPv6] as
much as possible; as explained in [IPConfig], creating IKEv2-
specific mechanisms should be avoided.
o Avoid the Not Invented Here (NIH) syndrome: There were several
proposals how to do IP address configuration in IKEv2, and the
IPsec WG chose one of them. Any significant changes should be
motivated by real technical needs, not by dislike of the proposal
that was chosen.
4.3. Implementation Considerations
The solution should have clean implementation dependencies. In
particular, it should not require significant modifications to the
core IPv6 stack (typically part of the operating system), or require
the IKE implementor to re-implement parts of the IPv6 stack (to,
e.g., have access or control to functionality that is currently not
exposed by public interfaces of the IPv6 stack).
4.4. Non-Goals
Mobile IPv6 already defines how it interacts with IPsec/IKEv2
[RFC4877], and the intent of this document is not to change that
interaction in any way.
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5. Solution Discussion
Assigning a new IPv6 address to the client creates a new "virtual
IPv6 interface", and "virtual link" between the client and the
gateway. We will assume that the virtual link has the following
properties:
o The link and its interfaces are created and destroyed by the IKEv2
process.
o The IPv6 addresses and prefixes are assigned to the link and its
interfaces by IKEv2 messages, and are removed once they are no
longer used by any IKE SA. An IKEv2 implementation may delay
removal of the IPv6 addresses and prefixes for a period of time to
allow upper layer protocol communications (e.g., a TCP connection)
to survive an IKE SA re-authentication that would use the same
addresses and prefixes.
o The link is not an IPsec SA; at any time, there can be zero or
more IPsec SAs covering traffic on this link.
o The link is not a single IKE SA; to support reauthentication, it
must be possible to identify the same link in another IKE SA.
o It is TBD whether a single IKE SA needs to support multiple
virtual links. (Possibly not; if multiple virtual links are
needed, multiple IKE_SAs could be used.)
o Not all IPsec-protected traffic between the peers is necessarily
related to the virtual link (although in the simplest VPN client-
to-gateway scenario it will be).
Given these assumptions and the goals described in the previous
section, it seems that the most important design choices to be made
are the following:
o What link/subnet model is used: in other words, the relationships
between VPN clients, IPv6 subnet prefixes, and link-local traffic
(especially link-local multicast).
o How information about the IPv6 prefix(es) is distributed from the
gateway to the clients.
o How to ensure unique IPv6 addresses for each client, and keep
forwarding state up-to-date accordingly..
o How layer 3 access control is done; in other words, where the
mechanisms for preventing address spoofing by clients are placed
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architecturally.
Each of these is discussed next in turn.
5.1. Link Model
There are at least three main choices how to organize the
relationships between VPN clients, IPv6 subnet prefixes, and link-
local traffic:
o Point-to-point link model: each VPN client is assigned one or more
IPv6 prefixes; these prefixes are not shared with other clients,
and there is no link-local traffic between different VPN clients
connected to the same gateway.
o Multi-access link model: multiple VPN clients share the same IPv6
prefix. Link-local multicast packets sent by one VPN client will
be received by other VPN clients (VPN gateway will forward the
packets, possibly with MLD snooping to remove unnecessary
packets).
o "Router aggregation" link model: one form of "multi-link" subnet
[Multilink] where multiple VPN clients share the same IPv6 prefix.
Link-local multicast will not be received by other VPN clients.
In the multi-access link model, VPN clients who are idle (i.e., not
currently sending or receiving application traffic) could receive
significant amounts of multicast packets from other clients
(depending on how many other clients are connected). This is
especially undesirable when the clients are battery-powered; for
example, a PDA which keeps the VPN connection to corporate intranet
active 24/7. For this reason, we will not consider the multi-access
link model in the rest of this document.
5.2. Distributing Prefix Information
Some types of addresses, such as CGAs, require knowledge about the
prefix before an address can be generated. The prefix information
could be distributed to clients in the following ways:
o IKEv2 messages (Configuration Payloads).
o Router Advertisement messages (sent over the IPsec tunnel).
o DHCPv6 messages (sent over the IPsec tunnel).
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5.3. Unique Address Allocation
In the "multi-access" and "router aggregation" link models (where a
single IPv6 prefix is shared between multiple VPN clients) mechanisms
are needed to ensure that one VPN client does not use an address
already used by some other client. Also, the VPN gateway has to know
which client is using which addresses in order to correctly forward
traffic.
The main choices seem to be the following:
o Clients receive the address(es) they are allowed to use in IKEv2
messages (Configuration Payloads). In this case, keeping track of
which client is using which address is trivial.
o Clients receive the address(es) they are allowed to use in DHCPv6
messages sent over the IPsec tunnel. In case the DHCPv6 server is
not integrated with the VPN gateway, the gateway may need to work
as a relay agent to keep track of which client is using which
address (and update its forwarding state accordingly).
o Clients can use stateless address autoconfiguration to configure
addresses and perform Duplicate Address Detection (DAD). This is
easy to do in multi-access link model, and can be made to work
with router aggretation link model if the VPN gateway traps NS
messages and spoofs NA replies. The gateway keeps track of which
client is using which address (and updates its forwarding state
accordingly) by trapping these NS/NA messages.
In the point-to-point link model, the client can simply use any
address from the prefix, and the VPN gateway only needs to know which
client is using which prefix in order to forward packets correctly.
5.4. Layer 3 Access Control
It is almost always desirable to prevent one VPN client from sending
packets with a source address that is used by another VPN client. In
order to correctly forward packets destined to clients, the VPN
gateway obviously has to know which client is using which address;
the question is therefore where, architecturally, the mechanisms for
ingress filtering are placed.
o Layer 3 access control enforced by IPsec SAD/SPD: the addresses/
prefixes assigned to a VPN client are reflected in the traffic
selectors used in IPsec Security Association and Security Policy
Database entries, as negotiated in IKEv2.
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o The ingress filtering capability could be placed outside IPsec;
the traffic selectors in SAD/SPD entries would cover traffic that
would be dropped later by ingress filtering.
The former approach is used by the current IPv4 solution.
5.5. Other Considerations
VPN gateway state
In some combinations of design choices, the amount of state
information required in the VPN gateway depends not only on the
number of clients, but also on the number of addresses used by one
client. With privacy addresses and potentially some uses of
Cryptographically Generated Addresses (CGAs), a single client
could have a large number of different addresses (especially if
different privacy addresses are used with different destinations).
Virtual link identifier
Reauthentication requires a way to uniquely identify the virtual
link when a second IKE SA is created. Some possible alternatives
are the IKE SPIs of the IKE SA where the virtual link was
"created" (assuming we can't have multiple virtual links within
the same IKE SA), a new identifier assigned when the link is
created, or any unique prefix or address that remains assigned to
the link for its entire lifetime. Currently, Section 6 proposes
that the gateway assigns a new IKEv2 Link ID when the link is
created. The client treats the Link ID as an opaque octet string;
the gateway uses it to identify relevant local state when
reauthentication is done.
Note that the link is not uniquely identified by the IKE peer
identities (because IDi is often a user identity that can be used
on multiple hosts at the same time), or the outer IP addresses of
the peers (due to NAT Traversal and [MOBIKE]).
Prefix lifetime
Prefixes could remain valid either for the lifetime of the IKE SA,
until explicitly cancelled, or for an explicitly specified time.
Currently, Section 6 proposes that prefixes remain valid for the
lifetime of the IKE SA (and its continuations via rekeying, but
not reauthentication). If necessary, the VPN gateway can thus add
or remove prefixes by triggering reauthentication. It is assumed
that adding or removing prefixes is a relatively rare situation,
and thus this draft does not currently specify more complex
solutions (such as explicit prefix lifetimes, or use of CFG_SET/
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CFG_ACK).
Compatibility with other IPsec uses
Compatibility with other IPsec uses probably requires that when a
CHILD_SA is created, both peers can determine whether the CHILD_SA
applies to the virtual interface (at the end of the virtual link),
or the real interfaces IKEv2 messages are being sent over. This
is required to select the correct SPD to be used for traffic
selector narrowing and SA authorization in general.
One straight-forward solution would be to add an extra payload to
CREATE_CHILD_SA requests, containing the virtual link identifier.
Requests not containing this payload would refer to the real link
(over which IKEv2 messages are being sent).
Another solution is to require that the peer requesting a CHILD_SA
proposes traffic selectors that identify the link. For example,
if TSi includes the peer's "outer" IP address, it's probably
related to the real interface, not the virtual one. Or if TSi
includes any of the prefixes assigned by the gateway (or the link-
local or multicast prefix), it is probably related to the virtual
interface.
These heuristics can work in many situations, but have proved
inadequate in the context of IPv6-in-IPv4 tunnels [RFC4891] and
Provider Provisioned VPNs [VLINK] [RFC3884], and Mobile IPv6
[RFC4877]. Thus, currently Section 6 proposes including the
virtual link identifier in all CREATE_CHILD_SA requests that apply
to the virtual interface.
Example about other IPsec uses:
If a VPN gateway receives a CREATE_CHILD_SA request associated
with a physical Ethernet interface, requesting SA for (TSi=FE80::
something, dst=*), it would typically reject the request (or in
other words, narrow it to an empty set) because it doesn't have
SPD/PAD entries that would allow joe.user@example.com to request
such CHILD_SAs.
(However, it might have SPD/PAD entries that would allow
"neighboring-router.example.com" to create such SAs, for
protecting e.g. some routing protocol that uses link-local
addresses.)
However, the virtual interface created when joe.user@example.com
authenticated and sent INTERNAL_IP6_LINK would have a different
SPD/PAD, which would allow joe.user@example.com to create this SA.
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6. Solution Sketch
This solution is basically a combination of (1) point-to-point link
model, (2) prefix information distributed in IKEv2 messages, and (3)
access control enforced by IPsec SAD/SPD.
(Second preliminary version, based on discussions with Tero Kivinen.)
6.1. Initial Exchanges
1) During IKE_AUTH, the client sends a new configuration attribute,
INTERNAL_IP6_LINK, which requests a virtual link to be configured.
The attribute contains the client's interface ID for link-local
address (other addresses may use other interface IDs). Typically,
the client would also ask for DHCPv6 server address; this is used
only for configuration, not address assignment.
To handle backward compatibility between a client that supports the
extended address configuration mechanism hereby specified and a VPN
gateway that does not, this specification RECOMMENDS that the VPN
client includes as well the INTERNAL_IP6_ADDRESS configuration
attribute to allow graceful fallback to the existing address
configuration mechanism specified in the IKEv2 specification [IKEv2],
unless it knows for sure that the VPN gateway supports the extended
mechanism hereby specified (e.g., via configuration.)
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(Client's Link-Local Interface ID)
INTERNAL_IP6_ADDRESS()
INTERNAL_IP6_DHCP() }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
To handle backward compatibility between a VPN gateway that supports
the extended address configuration mechanism hereby specified and a
client that does not, if the client has not sent the
INTERNAL_IP6_LINK configuration attribute the VPN gateway MUST NOT
include the INTERNAL_IP6_LINK configuration attribute in its reply
and should fallback to the address configuration mechanism specified
in the IKEv2 specification [IKEv2].
If the client has sent the INTERNAL_IP6_LINK configuration attribute,
the VPN gateway SHOULD ignore any INTERNAL_IP6_ADDRESS configuration
attribute present in the request.
The VPN gateway MUST choose for itself a link-local interface
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identifier different than the client's one, i.e., accept the link-
local interface identifier proposed by the client. In case the VPN
gateway cannot accept the link-local interface identifier the client
proposed, the VPN gateway MUST fail the IPv6 address assignment by
including a NOTIFY payload with the INTERNAL_ADDRESS_FAILURE message,
i.e., the IKE_SA can be created but no CHILD_SA will be created.
The VPN Gateway then replies with an INTERNAL_IP6_LINK configuration
attribute that contains the IKEv2 Link ID (which will be used for
reauthentication and CREATE_CHILD_SA messages), the client's link
local interface identier, and zero or more INTERNAL_IP6_PREFIX
attributes. The traffic selectors proposed by the initiator are also
narrowed to contain only the assigned prefixes, and the client link-
local address formed from the well-known link-local subnet prefix and
the client link-local interface identifier.
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK(Client's Link-Local Interface ID,
IKEv2 Link ID)
INTERNAL_IP6_PREFIX(Prefix1/64),
[INTERNAL_IP6_PREFIX(Prefix2/64),...],
[INTERNAL_IP6_DHCP(Address) ]
TSi = ((0, 0-65535,
FE80::<Client's Interface ID> -
FE80::<Client's Interface ID>)
(0, 0-65535,
Prefix1::0 -
Prefix1::FFFF:FFFF:FFFF:FFFF),
[(0, 0-65535,
Prefix2::0 -
Prefix2::FFFF:FFFF:FFFF:FFFF), ...])
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
At this point, the client can configure 1) its link-local address
from the well-known link-local subnet prefix (FE80::/64) and the
assigned client's link-local interface identifier, and 2) other non-
link-local unicast addresses from the assigned prefixes and any
proper interface identifier [IPv6Addr]. The VPN gateway MUST NOT
simultaneously assign the same prefixes to any other client, and MUST
NOT itself configure addresses from these prefixes. Thus, the client
does not have to perform Duplicate Address Detection (DAD). (This
approach is based on [IPv6PPP].)
The prefixes remain valid through the lifetime of the IKE SA (and its
continuations via rekeying). If the VPN gateway needs to remove a
prefix it has previously assigned, or assign a new prefix, it can do
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so by triggering reauthentication.
2) The client also contacts the DHCPv6 server. This is the
RECOMMENDED way to obtain additional configuration parameters (such
as the DNS server), as it allows easier extensibility and more
options (such as the domain search list for DNS).
6.2. Reauthentication
When the client performs reauthentication (and wants to continue
using the same "virtual link"), it includes the IKEv2 Link ID given
by the gateway in the INTERNAL_IP6_LINK attribute.
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(Client's Link Local Interface ID,
IKEv2 Link ID)
INTERNAL_IP6_DHCP() }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
The gateway uses the Link ID to look up relevant local state,
verifies that the authenticated peer identity associated with the
link is correct, and continues the handshake as usual.
6.3. Creating CHILD_SAs
As described in the previous section, both peers need to be able to
determine whether a CHILD_SA applies to the virtual interfaces, or
the real interfaces IKEv2 messages are being sent over.
Currently, this document proposes using an explicit indication
instead of relying on heuristics: the peers MUST include a LINK_ID
notification, containing the IKEv2 Link ID, in all CREATE_CHILD_SA
requests, including rekeys, that are related to the virtual link.
The LINK_ID notification is not included in the CREATE_CHILD_SA
response, or when doing IKE_SA rekeying.
6.4. Multicast
(The details of multicast use are to-be-determined.)
One way would be to create an SA for receiving multicast packets:
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TSi = (0, 0-65535,
FF00:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
<--
TSi = (0, 0-65535,
FF00:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
...and then use MLD as usual.
6.5. Relationship to Neighbor Discovery
Neighbor Discovery [IPv6ND] specifies the following mechanisms:
Router Discovery, Prefix Discovery, Parameter Discovery,and Address
Autoconfiguration are not used, as the necessary functionality is
implemented in IKEv2 layer.
Address Resolution, Next-hop Determination, and Redirect are not
used, as the virtual link does not have link-local addresses, and is
a point-to-point link.
Neighbor Unreachability Detection could be used, but is a bit
redundant given IKEv2 Dead Peer Detection.
Duplicate Address Detection is not needed, because this is a point-
to-point link, where the VPN gateway does not assign any addresses
from the global unicast prefixes, and link-local interface identifier
is negotiated separately.
6.6. Relationship to Existing IKEv2 Payloads
The mechanism described in this document is not intended to be used
at the same time as the existing INTERNAL_IP6_ADDRESS attribute. For
compatibility with gateways implementing only INTERNAL_IP6_ADDRESS,
the VPN client MAY include attributes for both mechanisms in
CFG_REQUEST. The capabilities and preferences of the VPN gateway
will then determine which is used.
All other attributes except INTERNAL_IP6_ADDRESS (and
INTENAL_ADDRESS_EXPIRY) from [IKEv2] remain valid, including the
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somewhat confusingly named INTERNAL_IP6_SUBNET (see Section 6.3 of
[RFC4718] for discussion).
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7. Payload Formats
7.1. INTERNAL_IP6_LINK Configuration Attribute
The INTERNAL_IP6_LINK configuration attribute is formatted as
follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!R| Attribute Type ! Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client's Link-Local |
| Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ IKEv2 Link ID ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Reserved (1 bit) - See [IKEv2].
o Attribute Type (15 bits) - INTERNAL_IP6_LINK (TBD1).
o Length (2 octets) - Length in octets of the Value field (Client's
Link-Local Interface ID and IKEv2 Link ID); 8 or more.
o Link-Local Interface ID (8 octets) - The Interface ID used for
link-local address (by the party that sent this attribute).
o IKEv2 Link ID (variable length) - The link ID (may be empty when
the client does not yet know the link ID).
7.2. INTERNAL_IP6_PREFIX Configuration Attribute
The INTERNAL_IP6_PREFIX configuration attribute is formatted as
follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!R| Attribute Type ! Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length |
+-+-+-+-+-+-+-+-+
o Reserved (1 bit) - See [IKEv2].
o Attribute Type (15 bits) - INTERNAL_IP6_PREFIX (TBD2).
o Length (2 octets) - Length in octets of the Value field; in this
case, 17.
o Prefix (16 octets) - An IPv6 prefix assigned to the virtual link.
The low order bits of the prefix field which are not part of the
prefix MUST be set to zero by the sender and MUST be ignored by
the receiver.
o Prefix Length (1 octets) - The length of the prefix in bits;
usually 64.
7.3. LINK_ID Notify Payload
The LINK_ID notification is included in CREATE_CHILD_SA requests to
indicate that the SA being created is related to the virtual link.
If this notification is not included, the CREATE_CHILD_SA requests is
related to the physical interface.
The Notify Message Type for LINK_ID is TBD3. The Protocol ID and SPI
Size fields are set to zero. The data associated with this
notification is the IKEv2 Link ID returned in the
INTERNAL_IP6_LINK_ID configuration attribute.
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8. IANA Considerations
This document defines two new IKEv2 configuration attributes, whose
values are to be allocated (have been allocated) from the "IKEv2
Configuration Payload Attribute Types" namespace [IKEv2]:
Multi-
Value Attribute Type Valued Length Reference
------ ---------------------- ------ ------------- ---------
TBD1 INTERNAL_IP6_LINK NO 8 or more [this doc]
TBD2 INTERNAL_IP6_PREFIX YES 17 octets [this doc]
This document also defines one new IKEv2 notification, whose value is
to be allocated (has been allocated) from the "IKEv2 Notify Message
Types - Status Types" namespace [IKEv2]:
Value Notify Messages - Status Types Reference
------ ------------------------------- ---------
TBD3 LINK_ID [this doc]
This document does not create any new namespaces to be maintained by
IANA.
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9. Security Considerations
To be written. (The security consideration should be pretty much the
same as for current configuration payloads.)
Assigning each client a unique prefix makes using randomized
interface identifiers [RFC4941] ineffective from privacy point of
view: the client is still uniquely identified by the prefix. In some
environments, it may be preferable to assign a VPN client the same
prefixes each time a VPN connection is established; other
environments may prefer assigning a different prefix every time for
privacy reasons. (This is basically a similar trade-off as in Mobile
IPv6 -- using the same Home Address forever is simpler than changing
it often, but has privacy implications.)
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10. Acknowledgments
The author would like to thank Patrick Irwin, Tero Kivinen, Julien
Laganier, Chinh Nguyen, Mohan Parthasarathy, Yaron Sheffer, Hemant
Singh, Dave Thaler, Yinghzhe Wu, and Fan Zhao for their valuable
comments.
Many of the challenges associated with IPsec-protected "virtual
interfaces" have been identified before: for example, in the context
of protecting IPv6-in-IPv4 tunnels with IPsec [RFC4891], Provider
Provisioned VPNs [VLINK] [RFC3884], and Mobile IPv6 [RFC4877]. Some
of the limitations of assigning a single IPv6 address were identified
in [RFC3314].
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11. References
11.1. Normative References
[IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[IPv6Addr]
Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
11.2. Informative References
[AUTOCONF]
Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[CGA] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2006.
[DHCPv6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[HBA] Bagnulo, M., "Hash Based Addresses (HBA)",
draft-ietf-shim6-hba-05 (work in progress), December 2007.
[IPConfig]
Aboba, B., Thaler, D., and L. Andersson, "Principles of
Internet Host Configuration", draft-iab-ip-config-04 (work
in progress), May 2008.
[IPv6ND] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[IPv6PPP] Varada, S., Haskins, D., and E. Allen, "IP Version 6 over
PPP", RFC 5072, September 2007.
[MLDv2] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[MOBIKE] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
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[Multilink]
Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
[NDProxy] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC3314] Wasserman, M., "Recommendations for IPv6 in Third
Generation Partnership Project 3GPP) Standards", RFC 3314,
September 2002.
[RFC3456] Patel, B., Aboba, B., Kelly, S., and V. Gupta, "Dynamic
Host Configuration Protocol (DHCPv4) Configuration of
IPsec Tunnel Mode", RFC 3456, January 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3884] Touch, J., Eggert, L., and Y. Wang, "Use of IPsec
Transport Mode for Dynamic Routing", RFC 3884,
September 2004.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4294] Loughney, J., Ed., "IPv6 Node Requirements", RFC 4294,
April 2006.
[RFC4718] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and
Implementation Guidelines", RFC 4718, October 2006.
[RFC4866] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
Optimization for Mobile IPv6", RFC 4866, May 2007.
[RFC4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
IKEv2 and the Revised IPsec Architecture", RFC 4877,
April 2007.
[RFC4891] Graveman, R., Parthasarathy, M., Savola, P., and H.
Tschofenig, "Using IPsec to Secure IPv6-in-IPv4 Tunnels",
RFC 4891, May 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[SHIM6] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
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Shim Protocol for IPv6", draft-ietf-shim6-proto-10 (work
in progress), February 2008.
[VLINK] Duffy, M., "Framework for IPsec Protected Virtual Links
for PPVPNs", draft-duffy-ppvpn-ipsec-vlink-00 (work in
progress), October 2002.
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Appendix A. Alternative Solution Sketches
A.1. Version -00 Sketch
The -00 version of this draft contained the following solution
sketch, which is basically a combination of (1) point-to-point link
model, (2) prefix information distributed in Neighbor Advertisements,
and (3) access control enforced outside IPsec.
1) During IKE_AUTH, client sends a new configuration attribute,
INTERNAL_IP6_LINK_ID, which requests a virtual link to be created.
The attribute contains the client's interface ID for link-local
address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID) }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
The VPN gateway replies with its own link-local interface ID (which
MUST be different from the client's) and an IKEv2 Link ID (which will
be used for reauthentication).
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID, IKEv2 Link ID) }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
At this point, both peers configure the virtual interface with the
link-local addresses.
2) The next step is IPv6 stateless address autoconfiguration; that
is, Router Solicitation and Router Advertisement messages sent over
the IPsec SA.
ESP(Router Solicitation:
src=:
dst=FF02:0:0:0:0:0:0:2) -->
<-- ESP(Router Advertisement:
src=FE80::<Gateway's Interface ID>
dst=FF02:0:0:0:0:0:0:1,
Prefix1, [Prefix2...])
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After receiving the Router Advertisement, the client can configure
unicast addresses from the advertised prefixes, using any interface
ID. The VPN gateway MUST NOT simultaneously assign the same prefixes
to any other client, and MUST NOT itself configure addresses from
these prefixes. Thus, the client does not have to perform Duplicate
Address Detection (DAD).
3) Reauthentication works basically the same way as in Section 6.2;
the client includes the IKEv2 Link ID in the INTERNAL_IP6_LINK_ID
attribute.
4) Creating and rekeying IPsec SAs works basically the same way as in
Section 6.3; the client includes the IKEv2 Link ID in those CHILD_SA
requests that are related to the virtual link.
Comments: This was changed in -01 draft based on feedback from VPN
vendors: while the solution looks nice on paper, it is claimed to be
unneccessarily complex to implement when the IKE implementation and
IPv6 stack are from different companies. Furthermore, enforcing
access control outside IPsec is a significant architectural change
compared to current IPv4 solutions.
A.2. Router Aggregation Sketch #1
The following solution was sketched during the IETF 70 meeting in
Vancouver together with Hemant Singh. It combines the (1) router
aggregation link model, (2) prefix information distributed in IKEv2
messages, (3) unique address allocation with stateless address
autoconfiguration (with VPN gateway trapping NS messages and spoofing
NA replies), and (4) access control enforced (partly) outside IPsec.
1) During IKE_AUTH, the client sends a new configuration attribute,
INTERNAL_IP6_LINK_ID, which requests a virtual link to be created.
The attribute contains the client's interface ID for link-local
address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID) }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
The VPN gateway replies with its own link-local interface ID (which
MUST be different from the client's), an IKEv2 Link ID (which will be
used for reauthentication and CREATE_CHILD_SA messages), and zero or
more INTERNAL_IP6_PREFIX attributes. The traffic selectors proposed
by the initiator are also narrowed to contain only the assigned
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prefixes (and the link-local prefix).
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID, IKEv2 Link ID),
INTERNAL_IP6_PREFIX(Prefix1/64),
[INTERNAL_IP6_PREFIX(Prefix2/64),...],
INTERNAL_IP6_DHCP(Address) ]
TSi = ((0, 0-65535,
FE80::<Client's Interface ID> -
FE80::<Client's Interface ID>)
(0, 0-65535,
Prefix1::0 -
Prefix1::FFFF:FFFF:FFFF:FFFF),
[(0, 0-65535,
Prefix2::0 -
Prefix2::FFFF:FFFF:FFFF:FFFF), ...])
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
2) The client now configures tentative unicast addresses from the
prefixes given by the gateway, and performs Duplicate Address
Detection (DAD) for them.
The Neighbor Solicitation messages are processed by the VPN gateway:
if the target address is already in use by some other VPN client, the
gateway replies with a Neighbor Advertisement. If the target address
is not already in use, the VPN gateway notes that it is now being
used by this client, and updates its forwarding state accordingly.
Comments: The main disadvantages of this solution are non-standard
processing of NS messages (which are used to update the gateway's
forwarding state), and performing access control partly outside
IPsec.
A.3. Router Aggregation Sketch #2
This is basically similar to the version -00 sketch described with
above, but uses router aggregation link model. In other words, it
combines (1) router aggregation link model, (2) prefix information
distributed in Neighbor Advertisements, (3) unique address allocation
with stateless address autoconfiguration (with VPN gateway trapping
NS messages and spoofing NA replies), and (4) access control enforced
outside IPsec.
1) During IKE_AUTH, client sends a new configuration attribute,
INTERNAL_IP6_LINK_ID, which requests a virtual link to be created.
The attribute contains the client's interface ID for link-local
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address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID) }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
The VPN gateway replies with its own link-local interface ID (which
MUST be different from the client's) and an IKEv2 Link ID (which will
be used for reauthentication).
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID, IKEv2 Link ID) }
TSi = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, 0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
At this point, both peers configure the virtual interface with the
link-local addresses.
2) The next step is IPv6 stateless address autoconfiguration; that
is, Router Solicitation and Router Advertisement messages sent over
the IPsec SA.
ESP(Router Solicitation:
src=:
dst=FF02:0:0:0:0:0:0:2) -->
<-- ESP(Router Advertisement:
src=FE80::<Gateway's Interface ID>
dst=FF02:0:0:0:0:0:0:1,
Prefix1, [Prefix2...])
3) The client now configures tentative unicast addresses from the
prefixes given by the gateway, and performs Duplicate Address
Detection (DAD) for them.
The Neighbor Solicitation messages are processed by the VPN gateway:
if the target address is already in use by some other VPN client, the
gateway replies with a Neighbor Advertisement. If the target address
is not already in use, the VPN gateway notes that it is now being
used by this client, and updates its forwarding state accordingly.
Comments: The main disadvantages of this solution are non-standard
processing of NS messages (which are used to update the gateway's
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forwarding state), and performing access control outside IPsec.
A.4. IPv4-like Sketch
This sketch resembles the current IPv4 configuration payloads, and it
combines (1) router aggregation link model, (2) prefix information
distributed in IKEv2 messages, (3) unique address allocation with
IKEv2 messages, and (4) access control enforced by IPsec SAD/SPD.
1) During IKE_AUTH, the client sends a new configuration attribute,
INTERNAL_IP6_LINK_ID, which requests a virtual link to be created.
The attribute contains the client's interface ID for link-local
address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID) }
TSi = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
The VPN gateway replies with its own link-local interface ID (which
MUST be different from the client's), an IKEv2 Link ID (which will be
used for reauthentication and CREATE_CHILD_SA messages), and zero or
more INTERNAL_IP6_ADDRESS2 attributes. Each attribute contains one
address from a particular prefix.
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK_ID(Link-Local Interface ID, IKEv2 Link ID),
INTERNAL_IP6_ADDRESS2(Prefix1+Client's Interface ID1),
[INTERNAL_IP6_ADDRESS2(Prefix2+Client's Interface ID2),...],
TSi = ((0, 0-65535,
FE80::<Client's Link-Local Interface ID> -
FE80::<Client's Link-Local Interface ID>)
(0, 0-65535,
Prefix1::<Client's Interface ID1> -
Prefix1::<Client's Interface ID1>),
[(0, 0-65535,
Prefix2::<Client's Interface ID2> -
Prefix2::<Client's Interface ID2>), ...])
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
Since the VPN gateway keeps track of address uniqueness, there is no
need to perform Duplicate Address Detection.
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2) If the client wants additional addresses later (for example, with
specific interface ID), it requests them in a separate
CREATE_CHILD_SA exchange. For example:
CP(CFG_REQUEST) =
{ INTERNAL_IP6_ADDRESS2(Prefix1+Client's Interface ID3) }
TSi = (0, 0-65535,
Prefix1::0 -
Prefix1::FFFF:FFFF:FFFF:FFFF>),
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) -->
If the requested address is not currently in use by some other
client, the VPN gateway simply returns the same address, and traffic
selectors narrowed appropriately.
CP(CFG_REQUEST) =
{ INTERNAL_IP6_ADDRESS2(Prefix1+Client's Interface ID3) }
TSi = ((0, 0-65535,
Prefix1::<Client's Interface ID3> -
Prefix1::<Client's Interface ID3>),
TSr = (0, 0-65535,
0:0:0:0:0:0:0:0 -
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
Comments: The main advantage of this solution is that it's quite
close to the current IPv4 way of doing things. By adding explicit
link creation (with Link ID for reauthentication/SPD selection, and
link-local addresses), and slightly changing the semantics (and also
name) of INTERNAL_IP6_ADDRESS attribute (can return more attributes
than was asked), we get much of the needed functionality.
The biggest disadvantages are probably potentially complex
implementation dependency for interface ID selection (see
Section 3.4), and the multi-link subnet model.
A.5. Sketch Based on RFC 3456
For completeness: a solution modeled after [RFC3456] would combine
(1) router aggregation link model, (2) prefix information
distribution and unique address allocation with DHCPv6, and (3)
access control enforced by IPsec SAD/SPD.
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Authors' Addresses
Pasi Eronen
Nokia Research Center
P.O. Box 407
FIN-00045 Nokia Group
Finland
Email: pasi.eronen@nokia.com
Julien Laganier
DOCOMO Communications Laboratories Europe GmbH
Landsberger Strasse 312
Munich D-80687
Germany
Phone: +49 89 56824 231
Email: julien.laganier.IETF@googlemail.com
Cheryl Madson
Cisco Systems, Inc.
510 MacCarthy Drive
Milpitas, CA
USA
Email: cmadson@cisco.com
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Eronen, et al. Expires May 22, 2009 [Page 36]
