[SR-Users] kamailio SBC - session timers

hi, i have kamailio+rtpengine acting as a SBC (private/public net interfaces) kamailio 5.4.x/rtpengine 9.x/centos 7 using TOPOH module modparam("topoh", "mask_ip", "public_IP") i'm rewriting IPs in INVITE like this  $var(ruri) = "sip:" + $(ru{re.subst,/private_IP/public_IP/g});                 $ru = $(ru{re.subst,/private_IP/public_IP/g});                 $tu = $(tu{re.subst,/private_IP/public_IP/g});                 $fu = $(fu{re.subst,/remote_private_IP/public_IP/g}); the same for route[WITHINDIALOG] and INVITE i have problem with session timers using re-INVITE method in the first INVITE SDP is correct c=IN IP4 public_IP but in the reinvite is c=IN IP4 private_IP and remote SBC drop with 422 because SDP is changed and SDP version is not. any tips / best practice? thanks Marek