[Serusers] Question about failure route

[Manuel Marin Garcia]

I am trying to implement a Failure route as follows:

modparam("tm", "fr_inv_timer", 15)
modparam("tm", "fr_timer", 10)

if ((uri=~"^sip:1[0-9]{10}@.*")) {
        route(4);
        break;
};


route[4] {
            rewritehostport("fisrtgatewayip:5060");
             t_on_failure("1");
            t_relay();
            break;
}


failure_route[1] {
        rewritehostport("secondgatewayip:5060");
        t_relay();
        break;

}

But I see that Failure route is never taken. After a SIP trace I see 
that SER always reply with 408 Request Timeout to the UA. Is there 
something wrong with routing logic or is there a way to avoid 408 
message to UA.

Please help!

Thanks