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
or something.
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:
----------------------------------------------------------------------
2.21. Error Handling
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:
o UNSUPPORTED_CRITICAL_PAYLOAD
o INVALID_SYNTAX
o AUTHENTICATION_FAILED
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.
--
kivi...@iki.fi
_______________________________________________
IPsec mailing list
IPsec@ietf.org
https://www.ietf.org/mailman/listinfo/ipsec
