*ns1 から ns2 へping
<pre>
$ sudo ip netns exec ns1 ping -c 3 192.0.2.2
PING 192.0.2.2 (192.0.2.2) 56(84) bytes of data.
64 bytes from 192.0.2.2: icmp_seq=1 ttl=64 time=0.461 ms
64 bytes from 192.0.2.2: icmp_seq=2 ttl=64 time=0.196 ms
64 bytes from 192.0.2.2: icmp_seq=3 ttl=64 time=0.187 ms
--- 192.0.2.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 0.187/0.281/0.461/0.127 ms
</pre>