IETF RFC 5723 PDF

The Internet Key Exchange version 2 (IKEv2) protocol has a certain computational and communication overhead with respect to the number of round trips required and the cryptographic operations involved. In remote access situations, the Extensible Authentication Protocol (EAP) is used for authentication, which adds several more round trips and consequently latency.

To re-establish security associations (SAs) upon a failure recovery condition is time consuming especially when an IPsec peer (such as a VPN gateway) needs to re-establish a large number of SAs with various endpoints. A high number of concurrent sessions might cause additional problems for an IPsec peer during SA re-establishment.

In order to avoid the need to re-run the key exchange protocol from scratch, it would be useful to provide an efficient way to resume an IKE/IPsec session. This document proposes an extension to IKEv2 that allows a client to re-establish an IKE SA with a gateway in a highly efficient manner, utilizing a previously established IKE SA.

A client can reconnect to a gateway from which it was disconnected. The proposed approach encodes partial IKE state into an opaque ticket, which can be stored on the client or in a centralized store, and is later made available to the IKEv2 responder for reauthentication. We use the term ticket to refer to the opaque data that is created by the IKEv2 responder. This document does not specify the format of the ticket but examples are provided.