[SR-Users] MetaSwitch ignores Contact: header

Dear list, I'm running kamailio-4.2.3-3.1.x86_64 in a very simple setup: one Asterisk server behind kamailio. But I'm using dispatcher, the other servers are just down currently. :) Different vendors route DIDs to kamailio's IP and kamailio handles the communication towards Asterisk. Now I have a new vendor who uses MetaSwitch, and there is a problem. All calls get dropped with a BYE from the Asterisk side after 32 seconds because Asterisk never receives the ACK, because kamailio doesn't forward it, because MetaSwitch sends it as ACK sip:number@KAMAILIO-IP instead of ACK sip:number@ASTERISK-IP That means MetaSwitch ignores what we tell it in the Contact: header. Is this MetaSwitch'es "fault" or kamailio's? All other vendors work fine without problems. Therefore I have compared an "old" vendor and the new one. Here is the result that shows the difference: Old vendor - works: OLDVENDOR-IP.5060 > KAMAILIO-IP.5060: INVITE sip:number@KAMAILIO-IP KAMAILIO-IP.5060 > OLDVENDOR-IP.5060: SIP/2.0 100 trying KAMAILIO-IP.5060 > ASTERISK-IP.5060: INVITE sip:number@KAMAILIO-IP ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 100 Trying ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK KAMAILIO-IP.5060 > OLDVENDOR-IP.5060: SIP/2.0 200 OK OLDVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number@ASTERISK-IP:5060 KAMAILIO-IP.5060 > ASTERISK-IP.5060: ACK sip:number@ASTERISK-IP:5060 New vendor with MetaSwitch - doesn't work: NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: INVITE sip:number@KAMAILIO-IP:5060 KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 100 trying KAMAILIO-IP.5060 > ASTERISK-IP.5060: INVITE sip:number@KAMAILIO-IP:5060 ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 100 Trying ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number@KAMAILIO-IP:5060 ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number@KAMAILIO-IP:5060 ASTERISK-IP.5060 > KAMAILIO-IP.5060: SIP/2.0 200 OK KAMAILIO-IP.5060 > NEWVENDOR-IP.5060: SIP/2.0 200 OK NEWVENDOR-IP.5060 > KAMAILIO-IP.5060: ACK sip:number@KAMAILIO-IP:5060 ... and so on ... Can I do something about this or is a change on MetaSwitch'es side in order? Thank you! Markus