by jcolp » Tue May 19, 2015 7:02 am
This is caused by res_pjsip defaulting to "yes" for force_rport. This option is compatible with pretty much everything but some of the Cisco SIP stacks. It causes SIP responses to go back to the source IP address and port, which is useful for NAT. In the case of Cisco however they send their messages from a randomized source port which drops traffic sent to it. The fix is to set "force_rport=no" for any endpoints which are Cisco phones.
Joshua Colp
Digium, Inc. | Senior Software Developer