1.4. The INFORMATIONAL Exchange

1.4. The INFORMATIONAL Exchange

At various points during the operation of an IKE SA, peers may desire to convey control messages to each other regarding errors or notifications of certain events. To accomplish this, IKE defines an INFORMATIONAL exchange. INFORMATIONAL exchanges MUST ONLY occur after the initial exchanges and are cryptographically protected with the negotiated keys. Note that some informational messages, not exchanges, can be sent outside the context of an IKE SA. Section 2.21 also covers error messages in great detail.

Control messages that pertain to an IKE SA MUST be sent under that IKE SA. Control messages that pertain to Child SAs MUST be sent under the protection of the IKE SA that generated them (or its successor if the IKE SA was rekeyed).

Messages in an INFORMATIONAL exchange contain zero or more Notification, Delete, and Configuration payloads. The recipient of an INFORMATIONAL exchange request MUST send some response; otherwise, the sender will assume the message was lost in the network and will retransmit it. That response MAY be an empty message. The request message in an INFORMATIONAL exchange MAY also contain no payloads. This is the expected way an endpoint can ask the other endpoint to verify that it is alive.

The INFORMATIONAL exchange is defined as:

Initiator Responder

HDR, SK {[N,] [D,] [CP,] ...} --> <-- HDR, SK {[N,] [D,] [CP], ...}

The processing of an INFORMATIONAL exchange is determined by its component payloads.