Basicamente, ele deve se parecer com isso (do sistema de trabalho com dois links de ethernet):
admin@mamba:~$ ip route show table all
default via 192.168.10.254 dev eth1 table admin
192.168.10.0/24 dev eth1 table admin scope link src 192.168.10.100
default via 192.168.20.254 dev eth0
192.168.20.0/24 dev eth0 proto kernel scope link src 192.168.20.100
192.168.10.0/24 dev eth1 proto kernel scope link src 192.168.10.100
admin@mamba:~$ ip rule show
0: from all lookup local
32764: from all to 192.168.10.100 lookup admin
32765: from 192.168.10.100 lookup admin
32766: from all lookup main
32767: from all lookup default