从空的路由表开始：
$ ip route show
# no output
然后为 eth1 （IP 10.120.5.16，网络掩码255.255.224.0）创建了路由表 101 ：
$ ip route add 10.120.0.0/19 dev eth1 src 10.120.5.16 table 101
$ ip rule add from 10.120.5.16 table 101
然后尝试为表 101 添加默认网关，但失败了：
$ ip route add default via 10.120.0.1 dev eth1 table 101
RTNETLINK answers: Network is unreachable
但是可以使用-I eth1 ping 10.120.0.1：
$ ping 10.120.0.1 -I eth1
PING 10.120.0.1 (10.120.0.1) from 10.120.5.16 eth1: 56(84) bytes of data.
64 bytes from 10.120.0.1: icmp_seq=1 ttl=255 time=1.49ms
64 bytes from 10.120.0.1: icmp_seq=1 ttl=255 time=1.52ms
并非没有指定接口：
$ ping 10.120.0.1
connect: Network is unreachable
问题：如何为路由表设置默认网关？
其他信息：
$ ip route show table 101
10.120.0.0/19 dev eth1 scope link src 10.120.5.16
$ ip rule show
0: from all lookup local
32765: from 10.120.5.16 lookup 101
32766: from all lookup main
32767: from all lookup default
操作系统：Ubuntu 14.04