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

Extensibility is good.  : )

On Mon, Oct 3, 2011 at 4:11 PM, Aron Rosenberg <arosenberg@xxxxxxxxxxxx> wrote:
What do you think about modifying the MarkListener class to give the App Writer control over inserts to black/gray list?


Aron Rosenberg
Sr. Director, Engineering,
LifeSize, a division of Logitech




On Mon, Oct 3, 2011 at 11:50 AM, Scott Godin <sgodin@xxxxxxxxxxxxxxx> wrote:
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]). 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

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@xxxxxxxxxxxx> 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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