Asterisk responds to wrong port - Asterisk 1.8

I am trying to troubleshoot a SIP register problem. If I understand this correctly, my Cisco 7961G (192.168.100.28) is requesting to the server to respond back to port 5060 from my Asterisk server (pbx.test.com = 192.168.100.200), but Asterisk is responding back to port 49162. In result, the c7961G does not hear the response and keep retransmitting over and over.

20:14:25.323452 IP (tos 0x60, ttl 64, id 221, offset 0, flags [none], proto UDP (17), length 654)
192.168.100.28.49162 > pbx.test.com.sip: SIP, length: 626
REGISTER sip:pbx.test.com SIP/2.0
Via: SIP/2.0/UDP 192.168.100.28:5060;branch=z9hG4bKb80890c0
From: sip:801@pbx.test.com;tag=00175ab1a9700003e06901fe-585543c8
To: sip:801@pbx.test.com
Call-ID: 00175ab1-a9700003-3d539bd6-199c0450@192.168.100.28
Max-Forwards: 70
Date: Wed, 16 Dec 2009 08:09:33 GMT
CSeq: 101 REGISTER
User-Agent: Cisco-CP7961G/8.5.3
Contact: sip:801@192.168.100.28:5060;transport=udp;+sip.instance=“urn:uuid:00000000-0000-0000-0000-00175ab1a970”;+u.sip!model.ccm.cisco.com="30018"
Supported: (null),X-cisco-xsi-7.0.1
Content-Length: 0
Expires: 3660

20:14:25.323606 IP (tos 0x60, ttl 64, id 38327, offset 0, flags [none], proto UDP (17), length 645)
pbx.test.com.sip > 192.168.100.28.49162: SIP, length: 617
SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.168.100.28:5060;branch=z9hG4bKb80890c0;received=192.168.100.28;rport=49162
From: sip:801@pbx.test.com;tag=00175ab1a9700003e06901fe-585543c8
To: sip:801@pbx.test.com;tag=as4f98f821
Call-ID: 00175ab1-a9700003-3d539bd6-199c0450@192.168.100.28
CSeq: 101 REGISTER
Server: pbx1.bestpathnetworks.com
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH
Supported: replaces, timer
Expires: 3600
Contact: sip:801@192.168.100.28:5060;transport=udp;expires=3600
Date: Tue, 17 May 2011 03:14:25 GMT
Content-Length: 0

what’s in sip.conf. Do you have any insecure= parameters set?

[801]
type=friend
directmedia=no
defaultuser=801
port=5060
nat=no
context=ep
host=dynamic
canreinvite=no
disallow=all
deny=0.0.0.0/0
permit=192.168.100.0/24
allow=gsm
allow=ulaw
allow=alaw
allow=g729

What version of 1.8 are you using?

Asterisk 1.8.4-1digium1~lucid

Try an Asterisk release out of the 1.8 SVN branch and see if that fixes it.

I should add, my c7961G’s are running SIP41.8.5.4S. They phones work find with Asterisk 1.6 with the same config.