I stumbled across an issue with Cisco’s “NAT Support for SIP” feature today. Some very long SIP invites (actually spanning two packets as a SIP continuation) were being truncated. The 1420 byte initial packet was losing 15 bytes, the 72 byte continuation was unaffected. A “debug ip nat sip” showed the error:
IPNAT SIP SDP: End of line beyond end of buffer.
It doesn’t seem this buffer can be tuned so this behaviour appears to be buggy. Nothing on the Cisco bug toolkit so I’ve raised a TAC request.
Comments and trackbacks
Did you find out a resolution for this issue?
Someone else contacted me about this post back in June 2008, below is my response. Not that helpful but an answer of sorts.
TAC didn’t have a fix for this (my request was 605942001) and they said SIP continuation was not supported. They raised an enhancement request and in the end we worked around the issue by using a shorter domain name to avoid the SIP continuation.
*** Service Request LOG 2007-07-06 13:14:55.0 GMT, CCARAMID, Action Type: Resolution Summary ***
updated bug for enhancement request with BU. Customer will try to implement workaround (fragmentation at l3 instead of l4)
*** Service Request LOG 2007-07-06 13:14:55.0 GMT, CCARAMID, Action Type: Problem Description ***
NAT SIP ALG currently cannot handle TCP segmented SIP messages. because of this the parser breaks the last line in the message upon translation
Leave a Response