Hi, I've been experimenting with the following setup: ipv6 ua --- ser (v6) --- msp gateway --- ser (v4) --- cisco 3640 pstn gateway --- cisco ip-phone Everything works fine with the IP phone but routing the call to the PSTN gateway causes it to return a 400 Malformed/Missing Request in response to the packet forwarded to it from ser(v4) If i use the ip-phone to make a call via the pstn gateway (i.e. involving only the V4 SER) everything is fine. This makes me believe that the most likely cause of the crash is that the PSTN gateway can not understand the IPv6 address in the Via: or the Record-Route: header fields If that is the case, where do people think would be the best place to remove the 'offending' fields and add them back when the reply comes back from the PSTN gateway ? The SERv4 server or the MSP gateway ? The last packet sent to the PSTN gateway is: Session Initiation Protocol Request-Line: INVITE sip:3007@128.16.67.2:5060 SIP/2.0 Message Header Record-Route: <sip:3007@128.16.234.7;ftag=49F56B1E;lr=on> Max-Forwards: 9 Record-Route: <sip:[2001:630:13:101:2E0:18FF:FE3E:ECB2];ftag=49F56B1E;l r =on> Via: SIP/2.0/UDP 128.16.234.7;branch=z9hG4bK86ba.d7fafbd5.0 Via: SIP/2.0/UDP 128.16.67.73:5062 Via: SIP/2.0/UDP [2001:630:13:101:2e0:18ff:fe3e:ecb2];branch=0 Via: SIP/2.0/UDP [2001:630:13:101:204:23ff:fe0b:dc58] CSeq: 6566 INVITE To: <sip:3007@128.16.234.7> Content-Type: application/sdp From: "Manish Lad" <sip:1006@frostie.cs.ucl.ac.uk>;tag=49F56B1E Call-ID: 1658003513 Subject: sip:1006@frostie.cs.ucl.ac.uk Content-Length: 185 User-Agent: KPhone/3.11 Contact: "NAT Proxy" <sip:proxy@128.16.67.73:5062;realuri=0-ralOcJk1sRAM 6AlMTdrMoAvMTMvMTAmO6IlNDdnMrZbObZaMGIvZGMqODip-bFj-sBk-cQz9WRl> Session Description Protocol Session Description, version (v): 0 Owner/Creator, Session Id (o): username 0 0 IN IP4 128.16.67.73 Session Name (s): The Funky Flow Connection Information (c): IN IP4 128.16.67.73 Time Description, active time (t): 0 0 Media Description, name and address (m): audio 32974 RTP/AVP 0 97 3 Media Attribute (a): rtpmap:0 PCMU/8000 Media Attribute (a): rtpmap:3 GSM/8000 Media Attribute (a): rtpmap:97 iLBC/8000 The reply from the gateway: Session Initiation Protocol Status-Line: SIP/2.0 400 Bad Request - 'Malformed/Missing Record Route' Message Header Via: SIP/2.0/UDP 128.16.234.7;branch=z9hG4bK86ba.d7fafbd5.0,SIP/2.0/UDP 128.16.67.73:5062,SIP/2.0/UDP [2001:630:13:101:2e0:18ff:fe3e:ecb2];branch=0,SIP / 2.0/UDP [2001:630:13:101:204:23ff:fe0b:dc58] From: "Manish Lad" <sip:1006@frostie.cs.ucl.ac.uk>;tag=49F56B1E To: <sip:3007@128.16.234.7>;tag=88098FAC-15AD Call-ID: 1658003513 CSeq: 6566 INVITE Content-Length: 0 Regards, Lambros