<pre>
$ sudo ip netns exec ns2 ip route add default via 198.51.100.254
</pre>
*ns1 から ns2 へ再度 ping
*エラーとはならないが、パケットロス100%
<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.
--- 198.51.100.1 ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2039ms
</pre>
*以下の設定を実施
<pre>
$ sudo ip netns exec router sysctl net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1
</pre>