[asterisk-users] SIP OPTIONS response from the peer is ignored - peer becomes UNREACHABLE

[Asterisk]

Hi guys,

I have one tricky question regarding SIP peers becoming unreachable.

I was logging the network traffic with Wireshark, and this is what it logged:

10:22:33.319719000 == sent from Asterisk to the phone:
OPTIONS sip:MyTestPhone at 172.11.8.30 SIP/2.0
Via: SIP/2.0/UDP 172.32.0.201:5060;branch=z9hG4bK417304ec;rport
From: "asterisk" <sip:asterisk at 172.32.0.201>;tag=as3399559b
To: <sip:MyTestPhone at 172.11.8.30>
Contact: <sip:asterisk at 172.32.0.201>
Call-ID: 3aacb84e634295120761deac4273dbba at 172.32.0.201
CSeq: 102 OPTIONS
User-Agent: Asterisk PBX
Max-Forwards: 70
Date: Thu, 25 Mar 2010 09:22:29 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Content-Length: 0

10:22:33.349331000 == received from the phone:
SIP/2.0 200 OK
Via: SIP/2.0/UDP 172.32.0.201:5060;branch=z9hG4bK417304ec;rport
From: "asterisk" <sip:asterisk at 172.32.0.201>;tag=as3399559b
To: <sip:MyTestPhone at 172.11.8.30>;tag=6B68E382-AD95AE0B
CSeq: 102 OPTIONS
Call-ID: 3aacb84e634295120761deac4273dbba at 172.32.0.201
Contact: <sip:MyTestPhone at 172.11.8.30>
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, INFO, MESSAGE, SUBSCRIBE, NOTIFY, PRACK, UPDATE, REFER
User-Agent: PolycomSoundPointIP-SPIP_430-UA/2.2.0.0047
Content-Length: 0

But at the same time, Asterisk reported:

Mar 25 10:22:33 NOTICE[1385] chan_sip.c: Peer 'MyTestPhone' is now UNREACHABLE!  Last qualify: 28

The phone became REACHABLE 10 seconds later when the first next OPTIONS request was sent from Asterisk. 

How is it possible that the peer becames UNREACHABLE eventhough Wireshark logged its proper response? This happened on a machine with older Asterisk version (1.2.16) but with all chan_sip.c patches installed. Were there any known problems in 1.2.x version related to this issue? I couldn't find anything remotely similar in the SVN patches...

Regards,
Alex