[Serusers] Another Looping Question

Hi All. Below is a snippet of an INVITE and you can see the usual "trying - your call is important to us" in the dialog. Anyhow, for some reason SER occasionally attempts to sent the ACK to itself, which causes a looping condition. The last ACK shown is the start of the looping condition. It only happens on occasion. SER should have consumed the ACK rather than attempted to forward it. Can anyone explain this? Regards, Paul IP Legend ------------------- 10.3.0.221 <http://10.3.0.221> - SER (behind a Cisco 3600 so ALG rewrote the IPs) 69.36.46.178 <http://69.36.46.178> - NATed SIP UA U 2005/04/15 02:19:16.252614 69.35.46.178:5060 <http://69.35.46.178:5060> -> 10.3.0.221:5060 <http://10.3.0.221:5060> INVITE sip:8187768080@sipdev.mycompany.net SIP/2.0. Via: SIP/2.0/UDP 192.168.1.102:5060 <http://192.168.1.102:5060> ;branch=z9hG4bK3915905414. From: Test User <sip:3215591439@sipdev.mycompany.net>;tag=1465261089. To: <sip:8187768080@sipdev.mycompany.net>. Call-ID: 2671219156(a)192.168.1.102. CSeq: 101 INVITE. Contact: <sip:3215591439@192.168.1.102:5060>. Proxy-Authorization: Digest username="3215591439", realm=" sipdev.mycompany.net <http://sipdev.mycompany.net>", nonce="425f5e0de25efdb3f5a6125dcf2147bf30fe9177", uri=" sip:8187768080@sipdev.mycompany.net", response="61996c3bdc10990fec7e245751777516", algorithm=MD5, cnonce="ae02e47a3355bada49ce344c92f48587", qop=auth, nc=00000002. max-forwards: 70. Allow: INVITE, ACK, CANCEL, BYE, REFER, NOTIFY. Content-Type: application/sdp. Content-Length: 180. . v=0. o=- 32014 3005 IN IP4 192.168.1.102 <http://192.168.1.102>. s=-. c=IN IP4 192.168.1.102 <http://192.168.1.102>. t=0 0. m=audio 13456 RTP/AVP 18 0 8 2 4 101. a=rtpmap:101 telephone-event/8000. a=fmtp:101 0-15. a=ptime:20. . # U 2005/04/15 02:19:16.276216 10.3.0.221:5060 <http://10.3.0.221:5060> -> 69.35.46.178:5060 <http://69.35.46.178:5060> SIP/2.0 100 trying -- your call is important to us. Via: SIP/2.0/UDP 192.168.1.102:5060 <http://192.168.1.102:5060> ;branch=z9hG4bK3915905414;rport=5060;received=69.35.46.178<http://69.35.46.178> . From: Test User <sip:3215591439@sipdev.mycompany.net>;tag=1465261089. To: <sip:8187768080@sipdev.mycompany.net>. Call-ID: 2671219156(a)192.168.1.102. CSeq: 101 INVITE. Content-Length: 0. . # U 2005/04/15 02:19:16.792795 69.35.46.178:5060 <http://69.35.46.178:5060> -> 10.3.0.221:5060 <http://10.3.0.221:5060> ACK sip:8187768080@sipdev.mycompany.net SIP/2.0. Via: SIP/2.0/UDP 192.168.1.102:5060 <http://192.168.1.102:5060> ;branch=z9hG4bK3499714875. From: Test User <sip:3215591439@sipdev.mycompany.net>;tag=1465261089. To: <sip:8187768080@sipdev.mycompany.net>;tag= cdbfe46960d7566fcbe09f199f2b328d.c2bb. Call-ID: 2671219156(a)192.168.1.102. CSeq: 100 ACK. Content-Length: 0. . # U 2005/04/15 02:19:16.912146 10.3.0.221:5060 <http://10.3.0.221:5060> -> 10.3.0.221:5060 <http://10.3.0.221:5060> ACK sip:8187768080@sipdev.mycompany.net SIP/2.0. Max-Forwards: 10. Record-Route: <sip:10.3.0.221 <http://10.3.0.221>;ftag=1465261089;lr>. Via: SIP/2.0/UDP 10.3.0.221 <http://10.3.0.221>;branch=0. Via: SIP/2.0/UDP 192.168.1.102:5060 <http://192.168.1.102:5060>;received= 69.35.46.178 <http://69.35.46.178>;branch=z9hG4bK3499714875. From: Test User <sip:3215591439@sipdev.mycompany.net>;tag=1465261089. To: <sip:8187768080@sipdev.mycompany.net>;tag= cdbfe46960d7566fcbe09f199f2b328d.c2bb. Call-ID: 2671219156(a)192.168.1.102. CSeq: 100 ACK. Content-Length: 0. P-hint: Local Destination.