Answering to myself: the I-CSCF routing logic contains a "append_branch()" on reception of the HSS LIR answer which is the cause of this use less fork Removed it and everything is fine Olivier De : sr-users-bounces(a)lists.sip-router.org [mailto:sr-users-bounces@lists.sip-router.org] De la part de DURECU, OLIVIER (OLIVIER) Envoyé : vendredi 21 mars 2014 17:39 À : sr-users(a)lists.sip-router.org Objet : [SR-Users] Kamailio ICSCF strange forking Hi all, I have deployed an IMS based on Kamailio 4.1.2 and I don't manage establishing a call. Users registration is OK but when I initiate the call from A@ims.net<mailto:A@ims.net> to B@ims.net<mailto:B@ims.net>, I notice a strange I-CSCF behavior The INVITE message goes OK from P-CSCF to S-CSCF then to I-CSCF. Till this point everything is fine... Then the I-CSCF performs its LIR diameter request and gets an Ok response from the HSS with a S-CSCF URI The I-CSCF forwards the INVITE at the received S-CSCF. BUT at the same time the I-CSCF generates a DNS request to resolve ims.net SIP SRV (it gets itself as answer...) and forwards a second INVITE (exact copy from the one sent to the S-CSCF) to itself So I have 2 copies of the same INVITE dialog travelling in the network and messing everything. Any idea of the cause of this behavior . Thanks for your support... Olivier