2.增加2个路由表分别是电信：a0 联通：b1
# vi /etc/iproute2/rt_tables
252 a0
251 b1

ip route flush table a0
ip route add default via 172.31.16.1 dev eth0 src 172.31.17.107 table a0
ip rule add from 172.31.17.107 table a0

ip route flush table b1
ip route add default via 172.31.32.1 dev eth1 src 172.31.43.225 table b1
ip rule add from 172.31.43.225 table b1