MTU/Path_MTU/marekについて、ここに記述してください。

First There Was the Fragmentation

Do-not-fragment bit

Another Black Hole

There are generally three solutions to this problem.

1) Reduce the MTU on the client side.

2) Reduce the MTU of all connections to the minimal value on the server side.

 The minimal required MTU for all IPv6 hosts is 1,280, which is fair. Unfortunately for IPv4 the value is 576 bytes.

To change the MTU setting you can type:
  ip -f inet6 route replace <> mtu 1280

3) Enable smart MTU black hole detection.