Hi, My computer has two NICs and was configured like below: auto lo > iface lo inet loopback > > auto eth0 > iface eth0 inet static > address 172.36.100.12 > network 172.36.100.0 > netmask 255.255.255.0 > broadcast 172.36.100.255 > up ip route add 172.36.100.0/24 dev eth0 src 172.36.100.12 table 10 > up ip route add default via 172.36.100.1 dev eth0 table 10 > up ip rule add from 172.36.100.12 table 10 > up ip route add 172.36.100.0/24 dev eth0 src 172.36.100.12 > > auto eth1 > iface eth1 inet static > address 172.36.100.13 > network 172.36.100.0 > netmask 255.255.255.0 > broadcast 172.36.100.255 > up ip route add 172.36.100.0/24 dev eth1 src 172.36.100.13 table 20 > up ip route add default via 172.36.100.1 dev eth1 table 20 > up ip rule add from 172.36.100.13 table 20 > up ip route add 172.36.100.0/24 dev eth1 src 172.36.100.13 I wrote a simple application to test the bound_addr with two NICs. The strange thing is when I call the URI, all the packet I captured with Wireshark is always sent from either eth0's address or eth1's address, no matter what bound_addr I set to. The IP in all headers is as same as bound_addr, except the CONTACT header. But the call still works. Then if I unplug the cable of this "default" interfaces, I cannot make the call but ping is still ok. My application is in the attachment. Any advice is welcome. *Bui Danh Quy*