RFC 5739
IPv6 Configuration in Internet Key Exchange Protocol Version 2 (IKEv2)
Internet Engineering Task Force (IETF) P. Eronen Request for Comments: 5739 Nokia Category: Experimental J. Laganier ISSN: 2070-1721 QUALCOMM, Inc. C. Madson Cisco Systems February 2010 IPv6 Configuration in Internet Key Exchange Protocol Version 2 (IKEv2)Abstract
When Internet Key Exchange Protocol version 2 (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 specifies new configuration attributes for IKEv2 that allows the VPN gateway to assign IPv6 prefixes to clients, enabling all features of IPv6 to be used with the client-gateway "virtual link". Status of This Memo This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation. This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5739.
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Table of Contents
1. Introduction and Problem Statement ..............................4 2. Terminology .....................................................5 3. Current Limitations and Goals ...................................6 3.1. Multiple Prefixes ..........................................6 3.2. Link-Local Addresses .......................................6 3.3. Interface Identifier Selection .............................7 3.4. Sharing VPN Access .........................................7 3.5. General Goals ..............................................8 3.6. Non-Goals ..................................................8 3.7. Additional Information .....................................9 4. Solution Details ................................................9 4.1. Initial Exchanges ..........................................9 4.2. Reauthentication ..........................................11 4.3. Creating CHILD_SAs ........................................11 4.4. Relationship to Neighbor Discovery ........................12 4.5. Relationship to Existing IKEv2 Payloads ...................13 5. Payload Formats ................................................13 5.1. INTERNAL_IP6_LINK Configuration Attribute .................13 5.2. INTERNAL_IP6_PREFIX Configuration Attribute ...............14 5.3. LINK_ID Notify Payload ....................................14 6. IANA Considerations ............................................15 7. Security Considerations ........................................15 8. Acknowledgments ................................................15 9. References .....................................................16 9.1. Normative References ......................................16 9.2. Informative References ....................................16 Appendix A. Design Rationale (Non-Normative) .....................19 A.1. Link Model ................................................20 A.2. Distributing Prefix Information ...........................20 A.3. Unique Address Allocation .................................21 A.4. Layer 3 Access Control ....................................21 A.5. Other Considerations ......................................22 A.6. Alternative Solution Sketches .............................24 A.6.1. Version -00 Sketch ....................................24 A.6.2. Router Aggregation Sketch #1 ..........................25 A.6.3. Router Aggregation Sketch #2 ..........................27 A.6.4. IPv4-Like Sketch ......................................28 A.6.5. Sketch Based on RFC 3456 ..............................30 Appendix B. Evaluation (Non-Normative) ...........................31
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(198.51.100.33) }, 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:
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", and it complicates or prevents using certain features of IPv6. Section 3 describes the limitations in detail. This document specifies new configuration attributes for IKEv2 that allows the VPN gateway to assign IPv6 prefixes to clients, enabling all features of IPv6 to be used with the client-gateway "virtual link".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]"); 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 implementations call "interface".3. Current Limitations and Goals
This section describes the limitations of the current IPv6 configuration mechanism and requirements for the new solution.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. The solution should support assigning addresses from multiple prefixes, without requiring the client to know beforehand how many prefixes are needed.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 the requirements in [IPv6Addr] and prevents the use of protocols that require link-local addresses, such as [MLDv2] and [DHCPv6].
The solution should assign link-local addresses to the virtual interfaces and allow them to be used for protocols between the VPN client and gateway.3.3. 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. This approach complicates the use of Cryptographically Generated Addresses (CGAs) [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 provide 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]. The solution should allow the VPN client to easily obtain several addresses from a given prefix, where the interface IDs are selected by the client and may depend on the prefix.3.4. 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), if allowed by the security policy. 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 [AUTOCONF]. 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.
The solution should support sharing the VPN access over a local area network connection when the other hosts are using stateless address autoconfiguration.3.5. General Goals
o The solution should avoid periodic messages over the VPN tunnel. o Reauthentication should work, where the client can start a new IKE Security Association (SA) and continue using the same addresses as before. o There should be compatibility with other IPsec uses. Configuring a virtual IPv6 link (with addresses assigned in IKEv2) should not prevent the same peers from using IPsec/IKEv2 for other uses (with other addresses). In particular, the peers may have Security Policy Database (SPD) entries and Peer Authorization Database (PAD) Child SA Authorization Data entries that are not related to the virtual link; when a CHILD_SA is created, it should be unambiguous which entries are used. o There should be 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 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 IKEv2 implementor to re-implement parts of the IPv6 stack (e.g., to have access or control to functionality that is currently not exposed by interfaces of the IPv6 stack). o Re-use existing mechanisms as much as possible, as described in [IPConfig]. Appendix A describes the rationale of why this document nevertheless uses IKEv2 configuration payloads for configuring the addresses. However, Section 4.1 recommends using a DHCPv6 Information-Request message for obtaining other configuration information (such as DNS server addresses).3.6. 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.
3.7. Additional Information
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 be avoided. The original 3GPP specifications 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. Due to similar concerns, the IEEE 802.16 IPv6 Convergence Sublayer [RFC5121] and Proxy Mobile IPv6 [RFC5213] also assign unique prefixes.4. Solution Details
4.1. Initial Exchanges
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 the link-local address (other addresses may use other interface IDs). Typically, the client would also ask for the DHCPv6 server address; this is used only for configuration (such as DNS server addresses), not address assignment. CP(CFG_REQUEST) = { INTERNAL_IP6_LINK(Client's Link-Local Interface 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) --> 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 identifier different than the client's, 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.
The VPN gateway then replies with an INTERNAL_IP6_LINK configuration
attribute that contains the IKEv2 Link ID (an identifier selected by
the VPN gateway, treated as an opaque octet string by the client --
this will be used for reauthentication and CREATE_CHILD_SA messages),
the gateway's link-local interface identifier, 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 (FE80::<Client's Interface ID>)
identifier.
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK(Gateway'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 its link-local address
(FE80::<Client's Interface ID>) and other non-link-local unicast
addresses from the assigned prefixes (with 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
so with reauthentication (either starting reauthentication itself or
requesting the client to reauthenticate using [RFC4478]).
The client also contacts the DHCPv6 server. This is the RECOMMENDED
way to obtain additional configuration parameters (such as DNS server
addresses), as it allows easier extensibility and more options (such
as the domain search list for DNS).
4.2. 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) --> At this point, the gateway MUST verify that the client is indeed allowed to use the link identified by the IKEv2 Link ID. The same situation occurs in [IKEv2] when the client wants to continue using the same IPv4 address with the INTERNAL_IP4_ADDRESS configuration attribute. Typically, the gateway would use the Link ID to look up relevant local state and compare the authenticated peer identity of the IKE_SA with the local state. If the client is allowed to continue using this link, the gateway replies (see Section 4.1) with the same gateway's link-local interface ID and IKEv2 Link ID as used earlier and sends the IPv6 prefix(es) associated with this link. Usually, the IPv6 prefix(es) will also be the same as earlier, but this is not required. If the client is not allowed to continue using this link, the gateway treats it as a request for a new virtual link, selects a different IKEv2 Link ID value, and replies as in Section 4.1.4.3. Creating CHILD_SAs
When a CHILD_SA is created, the peers need to determine which SPD entries and PAD Child SA Authorization Data entries are used for this CHILD_SA. In the basic client-to-VPN-gateway uses, the situation is simple: all the matching SPD entries and Child SA Authorization Data entries are related to the "virtual link" between the VPN client and the VPN gateway. However, if the same peers are also using IPsec/ IKEv2 for other uses (with addresses not assigned inside IKEv2), they would also have SPD entries and PAD Child SA Authorization Data that is not related to the virtual link. If one of the peers requests a CHILD_SA and proposes traffic selectors covering everything (like in Figure 2), should those be narrowed to the prefixes configured with INTERNAL_IP6_PREFIX or to
the other SPD/PAD entries? While some kind of heuristics are possible (see Appendix A for discussion), this document specifies an explicit solution: 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.4.4. 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. Address Resolution, Next-hop Determination, and Redirect are not used, as the virtual link does not have link-layer 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 the link-local interface identifier is negotiated separately. Duplicate Address Detection is not needed for global unicast addresses formed from the global unicast prefix(es) configured as part of the IKEv2 exchange, because this is a point-to-point link, where the VPN gateway does not assign any addresses from the global unicast prefixes. Duplicate Address Detection may be needed for link-local addresses, e.g., when the client configures a link-local address as per [RFC4941]. Thus, Duplicate Address Detection MAY be skipped for global unicast addresses formed from the global unicast prefix(es) configured as part of the IKEv2 exchange. However, Duplicate Address Detection for link-local unicast addresses MUST be performed as required per some other specifications, e.g., [RFC4941].
4.5. 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 somewhat confusingly named INTERNAL_IP6_SUBNET (see Section 6.3 of [RFC4718] for discussion).5. Payload Formats
5.1. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link-Local | | Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ IKEv2 Link ID ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Reserved (1 bit) - See [IKEv2]. o Attribute Type (15 bits) - INTERNAL_IP6_LINK (17). o Length (2 octets) - Length in octets of the Value field (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). The Link ID is selected by the VPN gateway and is treated as an opaque octet string by the client.
5.2. INTERNAL_IP6_PREFIX Configuration Attribute
The INTERNAL_IP6_PREFIX 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Prefix | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | +-+-+-+-+-+-+-+-+ o Reserved (1 bit) - See [IKEv2]. o Attribute Type (15 bits) - INTERNAL_IP6_PREFIX (18). 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 that 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 octet) - The length of the prefix in bits; usually 64.5.3. 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 are related to the real interface. The Notify Message Type for LINK_ID is 16414. 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 configuration attribute.
6. IANA Considerations
This document defines two new IKEv2 configuration attributes, whose values have been allocated from the "IKEv2 Configuration Payload Attribute Types" namespace [IKEv2]: Multi- Value Attribute Type Valued Length Reference ------ ---------------------- ------ ------------- --------- 17 INTERNAL_IP6_LINK NO 8 or more [RFC5739] 18 INTERNAL_IP6_PREFIX YES 17 octets [RFC5739] This document also defines one new IKEv2 notification, whose value has been allocated from the "IKEv2 Notify Message Types - Status Types" namespace [IKEv2]: Value Notify Messages - Status Types Reference ------ ------------------------------- --------- 16414 LINK_ID [RFC5739] This document does not create any new namespaces to be maintained by IANA.7. Security Considerations
Since this document is an extension to IKEv2, the security considerations in [IKEv2] apply here as well. The mechanism described in this document assigns each client a unique prefix, which makes using randomized interface identifiers [RFC4941] ineffective from a 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 prefix 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.)8. Acknowledgments
The authors would like to thank Patrick Irwin, Tero Kivinen, 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].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", BCP 14, RFC 2119, March 1997.9.2. 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)", RFC 5535, June 2009. [IPConfig] Aboba, B., Thaler, D., Andersson, L., and S. Cheshire, "Principles of Internet Host Configuration", RFC 5505, May 2009. [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.
[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. [RFC4478] Nir, Y., "Repeated Authentication in Internet Key Exchange (IKEv2) Protocol", RFC 4478, 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.
[RFC5121] Patil, B., Xia, F., Sarikaya, B., Choi, JH., and S. Madanapalli, "Transmission of IPv6 via the IPv6 Convergence Sublayer over IEEE 802.16 Networks", RFC 5121, February 2008. [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. [SHIM6] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming Shim Protocol for IPv6", RFC 5533, June 2009. [VLINK] Duffy, M., "Framework for IPsec Protected Virtual Links for PPVPNs", Work in Progress, October 2002.
Appendix A. Design Rationale (Non-Normative)
This appendix describes some of the reasons why the solution in Section 4 was selected and lists some alternative designs that were considered but were ultimately rejected. 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 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 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 Section 3, it seems that the most important design choices to be made are the following: o What link/subnet model is used; in other words, how relationships between VPN clients, IPv6 subnet prefixes, and link-local traffic (especially link-local multicast) are organized. 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 architecturally. Each of these is discussed next in turn.
A.1. Link Model
There are at least three main choices for 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 Multicast Listener Discovery (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 such as a PDA that keeps the VPN connection to corporate intranet active 24/7. For this reason, using the multi-access link model was rejected. The configuration attributes specified in Section 4 use the point-to- point link model.A.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) In Section 4, the prefix information is distributed in IKEv2 messages.
A.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 a multi-access link model and can be made to work with a router aggregation link model if the VPN gateway traps Neighbor Solicitation (NS) messages and spoofs Neighbor Advertisement (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.A.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 could be enforced by IPsec Security Association Database (SAD) / SPD; the addresses/prefixes assigned to a VPN client would be reflected in the traffic selectors used in IPsec Security Association and Security Policy Database entries, as negotiated in IKEv2.
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 and the
mechanism specified in Section 4.
A.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 Security Parameter Indexes (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. Section 4
specifies 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.
In Section 4, the prefixes remain valid for the lifetime of the
IKE SA (and its continuations via rekeying but not via
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 document does not specify more complex solutions
(such as explicit prefix lifetimes or use of CFG_SET/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 over which IKEv2 messages are being sent.
This is required to select the correct SPD to be used for traffic-
selector narrowing and SA authorization in general.
One straight-forward solution is 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],
Provider Provisioned VPNs ([VLINK], [RFC3884]), and Mobile IPv6
[RFC4877]. Thus, Section 4 includes the virtual link identifier
in all CREATE_CHILD_SA requests that apply to the virtual
interface.
Example of other IPsec uses:
If a VPN gateway receives a CREATE_CHILD_SA request associated
with a physical Ethernet interface, requesting an 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 to protect,
for example, 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.
A.6. Alternative Solution Sketches
A.6.1. Version -00 Sketch
The -00 version of this document contained the following solution
sketch, which is basically a combination of (1) a point-to-point link
model, (2) prefix information distributed in Neighbor Advertisements,
and (3) access control enforced outside IPsec.
1. During IKE_AUTH, the client sends a new configuration attribute,
INTERNAL_IP6_LINK, which requests a virtual link to be created.
The attribute contains the client's interface ID for the link-
local address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(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
has to be different from the client's) and an IKEv2 Link ID (which
will be used for reauthentication).
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK(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...])
After receiving the Router Advertisement, the client can configure
unicast addresses from the advertised prefixes, using any proper
interface ID. The VPN gateway does not simultaneously assign the
same prefixes to any other client and does 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 4;
the client includes the IKEv2 Link ID in the INTERNAL_IP6_LINK
attribute.
4. Creating and rekeying IPsec SAs works basically the same way as
in Section 4.3; the client includes the IKEv2 Link ID in those
CHILD_SA requests that are related to the virtual link.
Comments: This was changed in the -01 version of this document based
on feedback from VPN vendors; while the solution looks nice on paper,
it is claimed to be unnecessarily 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.6.2. Router Aggregation Sketch #1
Hemant Singh helped sketch the following solution during the IETF 70
meeting in Vancouver. It combines (1) the 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, which requests a virtual link to be created.
The attribute contains the client's interface ID for the link-
local address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(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
has to 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 prefixes (and the link-local prefix).
CP(CFG_REPLY) =
{ INTERNAL_IP6_LINK(Link-Local Interface ID, IKEv2 Link ID),
INTERNAL_IP6_PREFIX(Prefix1/64),
[INTERNAL_IP6_PREFIX(Prefix2/64),...] }
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.6.3. Router Aggregation Sketch #2
This is basically similar to the version -00 sketch described above but uses the router aggregation link model. In other words, it combines (1) the router aggregation link model, (2) prefix information distributed in Neighbor Advertisements, (3) unique address allocation with stateless address autoconfiguration (with the VPN gateway trapping NS messages and spoofing NA replies), and (4) access control enforced outside IPsec. 1. During IKE_AUTH, the client sends a new configuration attribute, INTERNAL_IP6_LINK, which requests a virtual link to be created. The attribute contains the client's interface ID for the link- local address (other addresses may use other interface IDs). CP(CFG_REQUEST) = { INTERNAL_IP6_LINK(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 has to be different from the client's) and an IKEv2 Link ID (which will be used for reauthentication). CP(CFG_REPLY) = { INTERNAL_IP6_LINK(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
forwarding state) and performing access control outside IPsec.
A.6.4. IPv4-Like Sketch
This sketch resembles the current IPv4 configuration payloads and
combines (1) the 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, which requests a virtual link to be created.
The attribute contains the client's interface ID for the link-
local address (other addresses may use other interface IDs).
CP(CFG_REQUEST) =
{ INTERNAL_IP6_LINK(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
has to 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(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.
2. If the client wants additional addresses later (for example, with
a 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 the
appropriately narrowed traffic selectors.
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 the INTERNAL_IP6_ADDRESS attribute (which 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 3.3) and the multi-link subnet model.
A.6.5. Sketch Based on RFC 3456
For completeness: a solution modeled after [RFC3456] would combine
(1) the router aggregation link model, (2) prefix information
distribution and unique address allocation with DHCPv6, and (3)
access control enforced by IPsec SAD/SPD.
Appendix B. Evaluation (Non-Normative)
Section 3 describes the goals and requirements for IPv6 configuration in IKEv2. This appendix briefly summarizes how the solution specified in Sections 4 and 5 meets these goals. o (3.1) Assigning addresses from multiple prefixes is supported, without requiring the client to know beforehand how many prefixes are needed. o (3.2) Link-local addresses are assigned and can be used for protocols between the VPN client and gateway. o (3.3) The entire prefix is assigned to a single client, so the client can freely select any number of interface IDs (which may depend on the prefix). o (3.4) This document does not specify how the VPN client would share the VPN connection with other devices. However, since the entire prefix is assigned to a single client, the client could further assign addresses from it without requiring coordination with the VPN gateway. o (3.5) The solution does not add any new periodic messages over the VPN tunnel. o (3.5) Reauthentication works (see Section 4.2). o (3.5) The solution is compatible with other IPsec uses since the LINK_ID notification makes it unambiguous which CHILD_SAs are related to the virtual link and which are not (see Sections 4.3 and 5.3). o (3.5) The new mechanisms do not prevent the VPN client and/or gateway from implementing the INTERNAL_IP6_ADDRESS configuration attribute as well; however, the two mechanisms are not intended to be used simultaneously (see Section 4.5). o (3.5) Implementation dependencies are, obviously, implementation dependent (and their cleanliness somewhat subjective). Possible drawbacks of some alternative solutions are discussed in Appendix A.6. o (3.5) The mechanism for configuring the prefixes (configuration payloads) is specific to IKEv2, for reasons described in Appendix A. However, Section 4.1 recommends using DHCPv6 Information-Request message for obtaining other configuration information (such as DNS server addresses).
Authors' Addresses
Pasi Eronen Nokia Research Center P.O. Box 407 FIN-00045 Nokia Group Finland EMail: pasi.eronen@nokia.com Julien Laganier QUALCOMM Incorporated 5775 Morehouse Drive San Diego, CA 92121 USA Phone: +1 858 658 3538 EMail: julienl@qualcomm.com Cheryl Madson Cisco Systems, Inc. 510 MacCarthy Drive Milpitas, CA USA EMail: cmadson@cisco.com