可以ping一下外部ip地址看看是否可以ping通。
Demo：
root@linaro-alip:~# ping 114.114.114.114 -I wwan0
PING 114.114.114.114 (114.114.114.114) from 10.252.248.35 wwan0: 56(84) bytes of data.
64 bytes from 114.114.114.114: icmp_seq=1 ttl=91 time=184 ms
64 bytes from 114.114.114.114: icmp_seq=2 ttl=79 time=83.8 ms
64 bytes from 114.114.114.114: icmp_seq=3 ttl=67 time=91.6 ms
64 bytes from 114.114.114.114: icmp_seq=4 ttl=63 time=77.9 ms
64 bytes from 114.114.114.114: icmp_seq=5 ttl=93 time=79.6 ms
64 bytes from 114.114.114.114: icmp_seq=6 ttl=83 time=86.7 ms
64 bytes from 114.114.114.114: icmp_seq=7 ttl=68 time=84.8 ms
64 bytes from 114.114.114.114: icmp_seq=8 ttl=80 time=88.8 ms