ssh server not working, but "ssh localhost" works

[kangyu29]

I have one computer(computer A) with openssh-server installed, but other computers(computer B and C) in my home cannot ssh to it. They all connected to internet through a router.

computer-A: ubuntu 9.04, has openssh-server
computer-B: ubuntu netbook remix
computer-C: Centos 5, has openssh-server

A and B can ssh to C, but B and C cannot ssh to A. They all can ssh to outside ssh-servers(eg. a server at school).

The problem seems on A. I have re-installed ssh server, and tested with "ssh localhost". Everything went well, but still, cannot ssh to A from B and C.

Does anyone know what is going on here?

[SoftwareExplorer]

Are you using IP addresses or names? My computers sometimes don't like names and want IP addresses.

[koenn]

Does anyone know what is going on here?

Yes, most likely.

[jfmanamtr]

Also, can B & C ping A (by IP or by name)?

~John

[jdakhayman]

You can login locally, but not from the internet? Then it sounds like you may need to forward port 22 to your server address in your router.

[Rhubarb]

The problem seems on A. I have re-installed ssh server, ...

Yes, I know of this problem.

Your client computers (B and C) still have a fingerprint (or key, or whatever they're called) that you accepted when you first SSHed to computer A before you re-installed it.
Because you have since re-installed computer A, the fingerprint has changed - so your client SSH computers (B and C) get a fingerprint mismatch and will hence terminate the SSH connection attempt.

The easiest way to fix this up (though it's probably not the most elegant), is to simply delete the contents of your ~/.ssh directory on computers B and C. I would recommend you make a backup of your ~/.ssh directory first, just in case.
Then for every client ssh connection attempt you make on computers B and C to new SSH servers, you will be prompted to accept the fingerprint / key from the SSH server.

- Then everything should work nicely again
There may well be a more elegant way to do this, that does not delete the fingerprints / keys from other ssh server's you've previously connected to.

[jfmanamtr]

You can login locally, but not from the internet? Then it sounds like you may need to forward port 22 to your server address in your router.

@jdakhayman: I think he is doing the SSH internally. He has the 3 PCs (A, B & C). A & B can ssh to C, but C & B can't ssh to A. A, B & C can ssh to a PC outside the home.

Do you run any firewall software on PC A? Cause that also will cause troubles with incoming ssh.

~John

[koenn]

wouldn't if be easier if the OP just posts the exact error (copy paste from the terminal) he gets when he does ssh whoever@whereever in stead of having a bunch of people guessing at what the problem might be and randomly throwing solutions at it ?

[kangyu29]

Are you using IP addresses or names? My computers sometimes don't like names and want IP addresses.

I use ip address. something like: 192.168.10.2

[kangyu29]

Also, can B & C ping A (by IP or by name)?

~John

I didn't try this, I will try it later when I get home and let you know.