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I fail to use ssh connecting to my remote machine, the detail situation is as following:

  1. The remote machine is behind a firewall, but can be connected using ssh with port 45992. I used to connect to it before without any problem.

  2. My current internet looks like only supports http service, because I can surf the web but nothing else works

This is what I got when I tried to use ssh:

user@machinename:~$ ssh -p 45992 xxx.xxx.xxx.xxx -v
OpenSSH_5.5p1 Debian-4ubuntu6, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /home/user/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to xxx.xxx.xxx.xxx [xxx.xxx.xxx.xxx] port 45992.

then it just stuck here.

What the ISP may have done? And is there any way to get my ssh working again?

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2  
I had this problem at a university I was attending. All KEX_INIT packets were mangled. I asked why and they told me "SSH is not supported." At the same time, people would play WoW between classes. Jerks. –  amphetamachine Aug 31 '11 at 11:00
    
exactly same here –  zhanwu Aug 31 '11 at 11:06
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2 Answers

Here's a part of my remote machine's /etc/ssh/sshd_config:

Port 22
Port 443

In other words, I connect to my remote machine at port 443, which is usually used by HTTPS.

ssh piskvor@remotemachine.example.net -p 443

I've found that most places that employ traffic filtering won't mess with HTTPS (or traffic on HTTPS' port).

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53 is another good port to try out. It is used by DNS so most places will leave it untouched. –  jeffgao Sep 1 '11 at 17:14
    
@jeffgao: Interesting suggestion - 99% of DNS traffic happens on 53/udp though; I've seen firewalls blocking 53/tcp. Moreover, some places will block any outbound traffic on port 53, only allowing the use of their internal nameserver. –  Piskvor Sep 2 '11 at 10:03
    
That's true. But on the other side, my home ISP on which my ssh server locates blocks incoming http/https traffics. Port 53 is very unlikely to be blocked by my ISP. Also DNS primarily using upd makes it easy to differentiate ssh traffic from DNS requests on my router to perform QoS. –  jeffgao Sep 2 '11 at 15:47
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1) Ask your ISP (consult their T&Cs etc)

2) Run a simple service (e.g. echo service) on that port and try connecting with telnet client or netcat. SSH is more complex to diagnose, so start with something simple.

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1) I am trying to get information from the ISP, but no response yet; 2) I am sure that the remote machine is working well, and it is reachable with (only) port 45992, because I can connect to it when I use 3G internet. Just curious what the ISP did –  zhanwu Aug 31 '11 at 17:13
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