Below is the example from http://kamailio.org/docs/modules/3.2.x/modules/tm.htm : failure_route[0]{ if (t_check_status("5[0-9][0-9]")){ # I do not like the 5xx responses, # so I give another chance to "foobar.com", # and I drop all the replies to make sure that # they are not forwarded to the caller. t_drop_replies(); rewritehostport("foobar.com"); append_branch(); t_relay(); } } Why do append_branch() is present before t_relay(). I'm asking because I didn't used it in failure routes and call rerouting on various conditions worked great.