[reSIProcate] DNS graylist issue with non-INVITE transaction failures

[Scott Godin]

This problem is discussed in the following RFC's:
http://tools.ietf.org/html/rfc4320, http://tools.ietf.org/html/rfc4321

RFC Statements:

Without a provisional, a late final response is the same as no response at
all and will likely result in blacklisting the late- responding
element ([3<http://tools.ietf.org/html/rfc4320#ref-3>]).
If an element is delaying its final response at all, sending a 100 Trying
after Timer E reaches T2 prevents this blacklisting without damaging
recovery from unreliable transport failure.

4. Normative Updates to RFC 3261 <http://tools.ietf.org/html/rfc3261> 4.1.
Action 1 An SIP element MUST NOT send any provisional response with a
Status- Code other than 100 to a non-INVITE request. An SIP element MUST NOT
respond to a non-INVITE request with a Status-Code of 100 over any
unreliable transport, such as UDP, before the amount of time it takes a
client transaction's Timer E to be reset to T2. An SIP element MAY respond
to a non-INVITE request with a Status-Code of 100 over a reliable transport
at any time. Without regard to transport, an SIP element MUST respond to a
non- INVITE request with a Status-Code of 100 if it has not otherwise
responded after the amount of time it takes a client transaction's Timer E
to be reset to T2.



I believe the correct solution is for the proxy to send a 100 trying using
the guidelines above.

Scott

On Mon, Oct 3, 2011 at 1:45 PM, Aron Rosenberg <arosenberg at logitech.com>wrote:

> I have the following topology setup.
>
> Focus A  <--> Proxy A <--> Proxy B <--> User B
>
> User B does a SUBSCRIBE and INVITE to Focus A
>
> At some point, User B loses connectivity due to a WiFi dropout or other
> such network interface change that is transient.
> If Focus A sends a NOTIFY to User B, the NOTIFY to User B will fail with a
> *locally* generated 408 before Proxy B sends back a 503 or 504 message.
> Also because this is a non-INVITE transaction, no 100 Trying is sent by
> Proxy A or Proxy B.
>
> Now because this was a locally generated 408 error a DNS graylist entry is
> added for the IP Address of Proxy A since it was an in-dialog message that
> was sent based on a numerical IP Route header.
>
> This then causes all of Focus A's other traffic which is Routed through
> Proxy A to temporarily fail including new transactions.
>
> Another interesting side effect is that even though the original Route
> header did not include a transport= value (Route: x.x.x.x:port), resip will
> try to contact that IP:Port with TCP even though TCP was never part of the
> original DNS lookup (not in the SRV records).
>
> I can see a few possible ways to fix this issue:
>
> - Change Proxy A to send 100 Trying for non-INVITE transactions. This will
> change the TransactionState from "Trying" to "Connecting" which then won't
> trigger a graylist (requires Proxy changes)
> - Change TransactionState class to only graylist entries for INVITE
> transactions based on "mMachine==ClientInvite" since those are the only ones
> which seem to send 100 Trying messages.
> - Allow Application writer control over black/gray list.
>    - If we don't want to break source compatibility, we could modify the
> MarkListener class to add a new virtual function "before" insertion which
> could return true/false or allow modifying the Mark or Expirery.
>    - If we wanted to break source compatibility, we could modify the
> current onMark callback to have a new signature and be called before
> insertion allowing changing of the values.
>
> If anybody is interested, I have a full resip debug log showing this issue
> from Focus A's perspective.
>
> Aron Rosenberg
> Sr. Director, Engineering,
> LifeSize, a division of Logitech
>
>
>
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>
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