Thinking some more about this I think that there might not only be the
TCP PATH MTU issue, but also my list of protocols used by Tails was
incomplete. While it does not run by default I think I2P is supported
within Tails and it seems to have also UDP firewall requirements [1]
that need to be tested.
Regards,
Olli
[1]
https://geti2p.net/en/faq#ports