| IPSECME | D. Migault (Ed) |
| Internet-Draft | Ericsson |
| Intended status: Standards Track | D. Palomares |
| Expires: August 20, 2015 | Orange/LIP6 |
| February 16, 2015 |
MOBIKEv2: MOBIKE extension for Transport mode
draft-mglt-ipsecme-mobikev2-01.txt
MOBIKE, the IKEv2 Mobility and Multihoming Protocol is defined only for CHILD_SA using the tunnel mode. This document describes MOBIKEv2 that extends MOBIKE for CHILD_SA using also transport mode.
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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 [RFC2119].
This document uses the following terminology:
Currently, MOBIKE [RFC4555] provides mobility and multihoming capabilities only for CHILD_SA using the tunnel mode. On the other hand, a large set of VPN solutions rely on GRE/IP tunnels and IPsec protection of these tunnels uses the transport mode. Similarly, for example when traffic is offloaded from Radio Access Network to public WLAN, IPsec may also be used to secure application. Some applications, like the DNS, may prefer the transport mode instead of the tunnel mode. In any case, the use of the transport mode prevents these connection to benefit from mobility and multihoming otherwise provided by MOBIKE.
This document specifies MOBIKEv2 that extends MOBIKE [RFC4555] to the transport mode. By doing so, communication protected with IPsec transport mode can also benefit from multihoming and mobility capabilities.
The remaining of the document is as follows. Section 5 specifies how to negotiate the support of MOBIKEv2 with the creation of an CHILD_SA using the transport mode. Section 6 describes how updates and additional IP addresses are handled with the transport mode. Section 7 details how IP updates on CHILD_SA impact the databases.
We assume the reader is familiar with IPsec [RFC4301], IKEv2 [RFC7296] and with MOBIKE [RFC4555].
[RFC4555] section 3.2 states that the use of MOBIKE is indicated with the MOBIKE_SUPPORTED Notify Payload in the IKE_AUTH exchange. [RFC7296] section 1.3.1 states that the use of the transport mode is indicated by the USE_TRANSPORT_MODE Notify Payload in a Create Child exchange.
MOBIKE [RFC4555] section 1.2 considers outside its scope the use of mobility and multihoming with a CHILD_SA using the transport mode. As result, an Initiator is not supposed to send both an MOBIKE_SUPPORTED and a USE_TRANSPORT_MODE Notify Payload in its IKE_AUTH, and this case is left undefined. In case the Initiator sends these two payloads, possible Responder's behaviors may be:
As a result, the use MOBIKEv2 with CHILD_SA using the transport mode requires to clarify the combination of the MOBIKE_SUPPORTED and the USE_TRANSPORT_MODE Notify Payload in an IKE_AUTH exchange. This is the purpose of Section 5
MOBIKE updates the IP addresses using an UPDATE_SA_ADDRESSES Notify Payload. At the reception of the UPDATE_SA_ADDRESSES Notify Payload, the Responder identifies the concerned IKE_SA and associated CHILD_SA(s). The IP addresses of the Initiator is replaced in both the IKE_SA and the CHILD_SA(s) with the IP address of the IP header used to carry UPDATE_SA_ADDRESSES Notify Payload. The IKE_SA is actually stored in the IKEv2 application, whereas CHILD_SAs are in the SAD.
When MOBIKE is activated, the CHILD_SAs are using the tunnel mode of IPsec. Thus, updating the IP address requires the tunnel to be updated within the CHILD_SA as well as the Selectors (SPI, IP addresses) of the CHILD_SA in the SAD. MOBIKEv2 supports CHILD_SA with transport mode. In this case, updating the IP address requires updating the SPD Traffic Selectors within the CHILD_SA as well as the Selectors of the SAD. In addition, the Traffic Selectors of the SPD cache also need to be updated. This is the major change of MOBIKEv2 versus MOBIKE. Section 6 specifies the protocol details of MOBIKEv2 and Section 7 clarifies the impact on the various IPsec databases.
With MOBIKEv2 support of mobility and multihoming for a CHILD_SA using the transport mode results from the combination of the USE_TRANSPORT_MODE and MOBIKE_SUPPORTED Notify Payload within the IKE_AUTH exchange in the message containing the SA Payload. Outside of this scope MOBIKE_SUPPORTED Notify Payload is not expected as defined in [RFC4555] section 3.2.
With MOBIKEv2 the Initiator may initiate an IKE_AUTH exchange with the following combinations of the USE_TRANSPORT_MODE and MOBIKE_SUPPORTED Notify Payload.
As specified by IKEv2 [RFC7296] in section 1.3.1 and in MOBIKE [RFC4555] section 3.2, the Responder can respond with a USE_TRANSPORT_MODE or MOBIKE_SUPPORTED Notify Payload only if such payload has been previously provided by the Initiator while initiating a CHILD_SA negotiation during the IKE_AUTH exchange. Given these restrictions, with MOBIKEv2 the Responder may respond with the following combination of the USE_TRANSPORT_MODE and MOBIKE_SUPPORTED Notify Payload.
In case the response does not satisfy the Initiator, it MUST delete the CHILD_SA as specified in [RFC7296] section 1.3.1.
CHILD_SAs may be updated when a UPDATE_SA_ADDRESSES Notify Payload is received or when the other peer become unreachable, in which case, the newly assigned IP address has been provided by an ADDITIONAL_*_ADDRESS Notify Payload. This section details how CHILD_SA MUST be updated when the CHILD_SA uses the transport mode.
Updating the IP address of the CHILD_SA using the transport mode impacts the SPD cache. As a result, IP address MUST be checked against the SPD and the PAD before performing any update of the CHILD_SA, or before communication the IP address as an alternate IP address. More specifically:
Similarly to MOBIKE, the appropriated IP address is the newly acquired IP address considered by the Initiator (either when a mobility occurs or when an additional IP address is used). This IP address is provided by the Initiator to the Responder via the IP header of the UPDATE_SA_ADDRESSES Notify Payload.
Updating a CHILD_SA using the transport mode with a new IP address involves updating:
This section discusses the impact of MOBIKEv2 on the IPsec databases. Since implementation vary widely, we do not discuss how these updates MUST be performed.
The SPD MUST NOT be modified. Only the SPD cache needs to be modified. MOBIKE did not necessarily require update on the SDP cache, mostly because the Traffic Selectors are left unchanged with the tunnel mode. In fact, SPD Cache also have the outer IP addresses in its processing information (cf. section 4.1.2 of [RFC4301]). This information MAY be also defined in conjunction of the PAD, and eventually MAY be derived from the IP header of the IKE_INIT. However, this information is mostly used to negotiate the corresponding CHILD_SA, and for this reason, does not necessarily require to be updated. On the other hand as discussed in Appendix A.1 of [RFC4555], if this information is used to link the SPD cache entry to the CHILD_SA, then this information MUST be updated properly.
With MOBIKEv2 for CHILD_SA using the transport mode, the SPD Traffic Selectors MUST be updated, and as such, the SPD MUST be updated. For this reason the IP address MUST match the SPD and PAD before performing the update.
MOBIKE requires to update the Selector of the CHILD_SA as well as the content of the CHILD_SA (the Tunnel outer IP addresses). With MOBIKEv2 for CHILD_SA using the transport mode, there is no tunnel outer IP addresses to update. Instead the SDP Selectors in the CHILD_SA as well as the Selector of the CHILD_SA MUST be updated.
The PAD MUST NOT be updated.
Security Considerations regarding mobility and multihoming have already been expressed in [RFC4555].
The use of the transport mode makes visible and unprotected the IP header of the carried IP packet. This. This discloses privacy related information as the IP header indicates the end points communicating. This could be avoided with the tunnel mode as the end point was the Security Gateway.
They is no IANA consideration. The signaling provided by MOBIKE is sufficient.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4301] | Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. |
| [RFC4555] | Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555, June 2006. |
| [RFC7296] | Kaufman, C., Hoffman, P., Nir, Y., Eronen, P. and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, October 2014. |