1.4.1. Deleting an SA with INFORMATIONAL Exchanges
1.4.1. Deleting an SA with INFORMATIONAL Exchanges
ESP and AH SAs always exist in pairs, with one SA in each direction. When an SA is closed, both members of the pair MUST be closed (that is, deleted). Each endpoint MUST close its incoming SAs and allow the other endpoint to close the other SA in each pair. To delete an SA, an INFORMATIONAL exchange with one or more Delete payloads is
Kaufman, et al. Standards Track [Page 17] RFC 5996 IKEv2bis September 2010
sent listing the SPIs (as they would be expected in the headers of inbound packets) of the SAs to be deleted. The recipient MUST close the designated SAs. Note that one never sends Delete payloads for the two sides of an SA in a single message. If there are many SAs to delete at the same time, one includes Delete payloads for the inbound half of each SA pair in the INFORMATIONAL exchange.
Normally, the response in the INFORMATIONAL exchange will contain Delete payloads for the paired SAs going in the other direction. There is one exception. If, by chance, both ends of a set of SAs independently decide to close them, each may send a Delete payload and the two requests may cross in the network. If a node receives a delete request for SAs for which it has already issued a delete request, it MUST delete the outgoing SAs while processing the request and the incoming SAs while processing the response. In that case, the responses MUST NOT include Delete payloads for the deleted SAs, since that would result in duplicate deletion and could in theory delete the wrong SA.
Similar to ESP and AH SAs, IKE SAs are also deleted by sending an Informational exchange. Deleting an IKE SA implicitly closes any remaining Child SAs negotiated under it. The response to a request that deletes the IKE SA is an empty INFORMATIONAL response.
Half-closed ESP or AH connections are anomalous, and a node with auditing capability should probably audit their existence if they persist. Note that this specification does not specify time periods, so it is up to individual endpoints to decide how long to wait. A node MAY refuse to accept incoming data on half-closed connections but MUST NOT unilaterally close them and reuse the SPIs. If connection state becomes sufficiently messed up, a node MAY close the IKE SA, as described above. It can then rebuild the SAs it needs on a clean base under a new IKE SA.