Network Working Group P. Eronen
Internet-Draft Nokia
Expires: December 7, 2007 June 5, 2007
IPv6 Configuration in IKEv2
draft-eronen-ipsec-ikev2-ipv6-config-00.txt
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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.
Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Current Limitations . . . . . . . . . . . . . . . . . . . . . 6
3.1. Multiple Prefixes . . . . . . . . . . . . . . . . . . . . 6
3.2. Link-Local Addresses . . . . . . . . . . . . . . . . . . . 6
3.3. Receiving Multicast Traffic . . . . . . . . . . . . . . . 6
3.4. Interface Identifier Selection . . . . . . . . . . . . . . 6
3.5. Sharing VPN Access . . . . . . . . . . . . . . . . . . . . 7
4. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Main Requirements . . . . . . . . . . . . . . . . . . . . 8
4.2. Desirable Non-Functional Properties . . . . . . . . . . . 8
4.3. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Solution Sketches . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Link Model . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Virtual Link Properties . . . . . . . . . . . . . . . . . 10
5.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4. First Sketch . . . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20
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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(192.0.1.234),
INTERNAL_IP4_DNS(10.11.22.33) },
SAr2,
TSi = (0, 0-65535, 192.0.1.234-192.0.1.234),
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:DB8:99:88:77:66:55:44) },
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+").
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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].
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 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 [RFC3041].
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.
If sharing of VPN access is done, it is quite obviously easier if you
get more than one address (which avoids NAT), and with DHCPv6 prefix
delegation [RFC3633] you could even avoid [NDProxy].
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4. Design Goals
4.1. Main Requirements
o Client can obtain a whole prefix, and use arbitrary Interface IDs
without requiring IKEv2 signaling for each Interface ID.
o 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 (Optional/To be determined) Client can be assigned multiple
prefixes for use on other links; e.g. the client could advertise
these prefixes on a local WLAN link. Gateway routes traffic to
these prefixes to the client.
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 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.
4.2. Desirable Non-Functional Properties
o Clean implementation dependencies.
o Re-use existing mechanisms, such as [AUTOCONF] and [DHCPv6] as
much as possible; as explained in [IPConfig], creating IKEv2-
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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. Non-Goals
Mobile IPv6 already defines how it interacts with IPsec/IKEv2
[RFC4877], and this document is not changing any of that.
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5. Solution Sketches
5.1. Link Model
Currently, the rest of this section assumes the point-to-point link
model [Multilink]. In other words, the connection between the client
and the VPN gateway is treated as a virtual point-to-point link, and
prefixes assigned to this link are not shared with any other link
(other VPN clients connected to the same gateway).
Other possibilites (multi-access or NBMA) may need to be considered
as well...
5.2. Virtual Link Properties
Assigning a new IPv6 address to the client creates a new "virtual"
IPv6 interface, and "virtual link" between the client and the
gateway. The interface/link is created by some IKEv2 signaling, and
it is destroyed once it is no longer used by any IKE_SA. However:
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.
o The link is not uniquely identified by the IKE peer identities
(IDi and IDr) because IDi is often a user identity that can be
used on multiple hosts at the same time.
o The link is not uniquely identified by the outer IP addresses of
the peers (due to NAT Traversal and MOBIKE).
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).
5.3. Discussion
Reauthentication / virtual link identifier
For reauthentication to work, we need an identifier that uniquely
identifies the virtual link when the 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
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virtual links within the same IKE_SA), a new identifier given at
that time, or any unique prefix assigned to that link.
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.
Otherwise, things like traffic selector narrowing get tricky. The
simplest solution would be to add an extra payload to some
CREATE_CHILD_SA requests, containing e.g. the virtual link
identifier.
Prefix assignment
Prefixes could be assigned in IKEv2 messages or Router
Advertisements sent inside the tunnel. Both would work; both have
some advantages.
Duplicate Address Detection
DAD can be avoided if the prefixes are not shared with any other
link, and the VPN gateway does not configure any addresses from
those prefixes (similar as in [IPv6PPP]). But how does the client
know this is the case? We could specify that using some
particular IKE payload always means this; or we could add a flag
to some payload.
Ingress filtering
As with any other link (physical or virtual), the gateway would
use ingress filtering to prevent address spoofing. However, if
the peer is also a router, the filters can allow other prefixes
than those assigned to the virtual link. Should these filters be
visible in the traffic selectors negotiated inside IKE?
5.4. First Sketch
NOTE: this is still very preliminary, and may change completely!
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1) During IKE_AUTH, client sends a new Configuration Payload,
INTERNAL_IP6_LINK that contains the Interface ID it will use
for the link-local address (other addresses may use other
Interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(client_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 gateway replies with its own Interface ID for link-local address,
and a new identifier for the virtual link.
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK(link_id, gateway_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)
At this point, both peers configure the virtual interface with the
link-local addresses. (This step is pretty much based on [IPv6PPP])
2) The next step is unicast prefix configuration; this is
simply RS/RA sent over the IPsec SA (possibly followed by DHCPv6
if RA had the M flag set).
3) Creating and rekeying IPsec SAs: exchange initiator includes
N(LINK_ID) notification in the CREATE_CHILD_SA request.
The notification data contains the link_id.
4) Reauthentication: when creating a new IKE_SA, client includes
the link_id in INTERNAL_IP6_LINK CFG_REQUEST.
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6. IANA Considerations
This document has no IANA actions. (This may change in future
versions of this document.)
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7. Security Considerations
To be written. (The security consideration should be pretty much the
same as for current configuration payloads.)
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8. Acknowledgments
The author would like to thank Mohan Parthasarathy and Yaron Sheffer
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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9. References
9.1. 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.
9.2. Informative References
[AUTOCONF]
Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[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-03 (work in progress), June 2007.
[IPConfig]
Aboba, B. and D. Thaler, "Principles of Internet Host
Configuration", draft-aboba-ip-config-01 (work in
progress), May 2007.
[IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[IPv6ND] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[IPv6PPP] Varada, S., Haskins, D., and E. Allen, "IP Version 6 over
PPP", draft-ietf-ipv6-over-ppp-v2-03 (work in progress),
May 2007.
[MLDv2] Vida, R. and L. Costa, "Multicast Listener Discovery
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Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[Multilink]
Thaler, D., "Multilink Subnet Issues",
draft-iab-multilink-subnet-issues-03 (work in progress),
January 2007.
[NDProxy] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[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.
[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 4193, 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.
[SHIM6] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
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Shim Protocol for IPv6", draft-ietf-shim6-proto-08 (work
in progress), May 2007.
[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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Author's Address
Pasi Eronen
Nokia Research Center
P.O. Box 407
FIN-00045 Nokia Group
Finland
Email: pasi.eronen@nokia.com
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