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Yoav Nir writes:
> OK. One more try:
I think this is still bit confusing. How about splitting it to few subsections, i.e. 2.21. Error Handling 2.21.1 Error Handling in IKE_SA_INIT 2.21.2 Error Handling in IKE_AUTH 2.21.3 Error Handling after IKE SA is Authenticated 2.21.4 Error Handling Outside IKE SA
Now you need to be very careful when reading the text to understand when it is taking about IKE_AUTH or some other exchange and whether it is talking about errors in request and replies.
For example the text could look something like this:
There are many kinds of errors that can occur during IKE processing. The general rule is that if a request is received that is badly formatted, or unacceptable for reasons of policy (e.g., no matching cryptographic algorithms), the response contains a Notify payload indicating the error. Whether to send such response depends whether the there is authenticated IKE SA or not.
If there is an error parsing or processing response packet, then generic rule is not to send any error back, as responses should not generate new requests (which would be the only way to send error message back). Such errors in parsing or processing response packets should still take care to clean up the state (for example, by sending DELETEs for bad SAs).
Only authentication failures (AUTHENTICATION_FAILED) and malformed messages (INVALID_SYNTAX) lead to a deletion of the IKE SA without requiring an explicit INFORMATIONAL exchange carrying a DELETE payload. Other error conditions require such an exchange, if policy dictates that this is needed.
2.21.1 Error Handling in IKE_SA_INIT
Errors that occur before a cryptographically protected IKE SA is established must be handled very carefully. There is a trade-off between wanting to be helpful in diagnosing a problem and responding to it and wanting to avoid being a dupe in a denial of service attack based on forged messages.
In an IKE_SA_INIT exchange, any error notification causes the exchange to fail, although some, like COOKIE, INVALID_KE_PAYLOAD or INVALID_MAJOR_VERSION may lead to a subsequent successful exchange. Note, as all error notifications are completely unauthenticated, the recipient should not immediately act based on them (unless corrective actions are known like COOKIE, INVALID_KE_PAYLOAD etc), but continue trying for some time before giving up.
2.21.2 Error Handling in IKE_AUTH
All errors that occur in an IKE_AUTH exchange, causing the authentication to fail for whatever reason (invalid shared secret, invalid ID, untrusted certificate issuer, revoked or expired certificate, etc.) SHOULD result in an AUTHENTICATION_FAILED notification. If the error occurred on the responder, the notification is returned in the protected response, and is usually the only payload in that response. Note, that although the IKE_AUTH messages are encrypted and integrity protected, if the peer receiving this notification has not authenticated the other end yet, the information needs to be treated with caution.
If the error occurs on the initiator, the notification MAY be returned in a separate INFORMATIONAL exchange, usually with no other payloads. This is exception for the general rule of not starting new exchanges based on errors in responses.
Note, however, that request messages that contain an unsupported critical payload, or where the whole message is malformed (rather than just bad payload contents), MUST be rejected in their entirety, and only lead to an UNSUPPORTED_CRITICAL_PAYLOAD or INVALID_SYNTAX Notification sent as response. The receiver should not verify the payloads related to authentication in this case.
If authentication has succeeded in the IKE_AUTH exchange, the IKE SA is established, but establishing the child SA, or requesting configuration information may still fail. This failure does not automatically cause the IKE SA to be deleted. Specifically, a responder may include all the payloads associated with authentication (IDr, Cert and AUTH) while sending error notifications for the piggybacked exchanges (FAILED_CP_REQUIRED, INVALID_SELECTORS, NO_PROPOSAL_CHOSEN, etc.), and the initiator MUST NOT fail the authentication because of this. The initiator MAY, of course, for reasons of policy later delete such an IKE SA.
In an IKE_AUTH exchange, or in the INFORMATIONAL exchange immediately following it (in case error happened in when processing response to IKE_AUTH), only the following notifications cause the IKE SA to be deleted or not created, without a DELETE payload:
Extension documents may define new error notifications with these semantics, but MUST NOT use them unless the peer is known to understand them.
2.21.3 Error Handling after IKE SA is Authenticated
After the IKE SA is authenticated all requests having errors MUST result in response notifying about the error.
In normal situation there should not be cases where valid response from other end results in error situation in the initiator, so there should not be any reason for initiator to send error messages to the other end. Because sending such error messages as INFORMATIONAL exchange might lead to further errors causing loops such errors SHOULD NOT be sent. If such errors are seen that might mean that the peers do not have same state, thus it might be good to delete the IKE SA to clean up state and start over from the beginning.
Similarly if the responder parsing the request notices it is badly formatted (after it has passed the message authentication code checks and window checks) and it sends INVALID_SYNTAX notification back, then this error notification is considered fatal in both ends meaning that IKE SA is deleted without explicit delete payload.
2.21.4 Error Handling Outside IKE SA
A node MUST limit the rate at which it will send messages in response to unprotected messages.
If a node receives a message on UDP port 500 or 4500 outside the context of an IKE SA known to it (and not a request to start one), it may be the result of a recent crash of the node. If the message is marked as a response, the node MAY audit the suspicious event but MUST NOT respond. If the message is marked as a request, the node MAY audit the suspicious event and MAY send a response. If a response is sent, the response MUST be sent to the IP address and port from whence it came with the same IKE SPIs and the Message ID copied. The response MUST NOT be cryptographically protected and MUST contain a Notify payload indicating INVALID_IKE_SPI. The INVALID_IKE_SPI notification indicates an IKE message was received with an unrecognized destination SPI; this usually indicates that the recipient has rebooted and forgotten the existence of an IKE SA.
A node receiving such an unprotected Notify payload MUST NOT respond and MUST NOT change the state of any existing SAs. The message might be a forgery or might be a response, the genuine correspondent was tricked into sending. A node should treat such a message (and also a network message like ICMP destination unreachable) as a hint that there might be problems with SAs to that IP address and should initiate a liveness check for any such IKE SA. An implementation SHOULD limit the frequency of such tests to avoid being tricked into participating in a denial of service attack.
If an error occurs outside the context of an IKE request (e.g., the node is getting ESP messages on a nonexistent SPI), the node SHOULD initiate an INFORMATIONAL exchange with a Notify payload describing the problem.
A node receiving a suspicious message from an IP address (and port, if NAT traversal is used) with which it has an IKE SA SHOULD send an IKE Notify payload in an IKE INFORMATIONAL exchange over that SA. The recipient MUST NOT change the state of any SAs as a result, but may wish to audit the event to aid in diagnosing malfunctions. -- email@example.com _______________________________________________ IPsec mailing list IPsec@ietf.org https://www.ietf.org/mailman/listinfo/ipsec