obfs4 bridges often don't work (maybe MTU?)

There have been some reports of obfs4 bridges not working.

A user has found out on the router being used some error messages like:

ICMP 185.xx.xx.xx unreachable - need to frag (mtu 1456), length 556

This is not happenning with other bridges or pluggable transports.

I did some searches online and found out some information regarding MTU and encapsulating that I cannot really follow, like

http://opsmonkey.blogspot.com/2007/02/path-mtu-discovery-and-mtu.html

And in https://ubuntuforums.org/archive/index.php/t-979821.html I found a workaround but the user reports no change after applying it (ifconfig wlan0 mtu 1462)

Do we need to do something about this problem? I think obfs4 bridges need to use bigger packages. Maybe it is a documentation issue, or maybe the configuration should be changed when using obsf4 bridges.

Feature Branch: bugfix/9268-deal-with-smaller-MTU

Related issues

• Related to #12197 (closed)
• Related to #15168 (closed)
• Is duplicate of #15548

Original created by @emmapeel on 9268 (Redmine)