$ sudo ip netns exec router2 sysctl net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1
</pre>
*ns1から、ns2へpingを流すと、router1からパケットを届けることができなかったメッセージが帰る
<pre>
$ sudo ip netns exec ns1 ping -c 3 198.51.100.1
PING 198.51.100.1 (198.51.100.1) 56(84) bytes of data.
From 192.0.2.254 icmp_seq=1 Destination Net Unreachable
From 192.0.2.254 icmp_seq=2 Destination Net Unreachable
From 192.0.2.254 icmp_seq=3 Destination Net Unreachable
--- 198.51.100.1 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2025ms
</pre>