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Stuck SSH session

When logging from my laptop to remote SSH servers I had a strange problem. Whenever a big chunk of text needs to be returned, my SSH session would stuck and completely stop working. It would not disconnect, but just stay there doing nothing. I would have to log in again. By "big chunk" I mean something like 20+ lines. Output of "ps ax" for example.

This made me so mad, because if was working on server for a few minutes making sure that I "head" and "tail" every command to reduce output and then I would forget that some command might output more. For example, using "vi" or "mcedit" was completely impossible.

My Internet connection goes through PPPoE. Websites work fine, HTTP works really well, but SSH... no go. The server on the other side is behind a firewall, so tunneling and port forwarding are here.

I searched around, and found that TCP/IP packet size might be the problem, so I tried different MTU values for my PPPoE connection, but without much luck. I was able to get a little bit more before it would stuck again.

And then I landed on this Debian bug report from 2005:


Apparently still valid. It looks like it only relates to some D-Link routers, although I have no clue what's at the other end where the server is connected. The solution is to reduce MTU server-side. Luckily, I can still run a one-liner command, and so I did:

/sbin/ifconfig eth0 mtu 1000

Everything runs fine now. I just wonder if this would decrease server through-output on the local LAN where it runs.

Milan Babuškov, 2011-12-01
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