OpenSSH hangs after login without showing login prompt

Question

I ran across an issue with ssh after fresh Ubuntu 13.10 installation on Lenovo T420. I tried git pull (which failed) and this led me to more general ssh failing.

After spending some 2-3 hrs of beautiful Sunday morning I have established:

1. ssh is able to authenticate. see the log below. Also telnet google.com 80 hangs on connecting.
2. I can connect using putty - it shows motd and prompt
3. It doesn't work on both wired and wireless connections, also I tried cellular network.
4. I can successfully login to localhost

here be the log:

debug1: Authentication succeeded (keyboard-interactive).
Authenticated to web1.mydevil.net (via proxy).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LC_PAPER = pl_PL.UTF-8

and then just keeps sending

debug1: client_input_channel_req: channel 0 rtype [email protected] reply 1

without showing me the prompt and eventually disconnects.

I found out that telnet google.com 80 hangs on Connecting <IP-addr>... as well.

Solution

Okay, this on turned out to be WTF LOL squared...

I got a hint that it was most likely ICMP packets being filtered by the firewall. So when you stumble upon this issue check it out.

In the article I found on Hacker News one reads:

ssh did not work. It would connect, flip some data back and forth (as shown with -v) and then would hang.

Certain websites would become inaccessible.

Which were my symptomps that appeared after switching my wireless router to another device. Device in question was Linksys WRT-54G running dd-wrt.

Comments

[Martin von Wittich]

Have you checked /var/log/auth.log on the server for possible error messages?

[Maciej Jankowski]

Permission denied. as expected. this is not my machine.

[Martin von Wittich]

Hmm... is it possible that the server is somehow misconfigured? I'm not really sure how to debug this further. You could check the output of ssh -vvv if there's anything more interesting in the debug messages, but the client side log was rarely helpful for me when debugging issues like these.

[user2948306]

"Filter all ICMP and watch the world burn", indeed. I take it DD-WRT was the failing device, right?

[Maciej Jankowski]

yup, that seemed to be the problem. Maybe I messed something with its configuration. It worked on another device running dd-wrt.