I have:

a win2k pc
a linux (mandrake) pc
a fedora (core 2) pc
all on a lan (linksys router)

I just installed the core 2 pc. Completely fresh install.

The windows pc can ssh in to either of the linux pc's.

Neither linux PC can ssh to each other. The ssh command just times out, doesn't do anything or return to prompt.

I never added anything to hosts.allow on either linux box (and yet the windows pc can ssh to either one just fine).

what could cause this?

Recheck your sshd_config for clues. Use tcpdump to figure out whether you are getting any responses from the server. Could it be a protocol problem?

sshclient is using protocol 2, sshd using protocol 1 or vice versa...

Can you ping, et cetera, from one to the other?

Each machine can ping the other.

Here is /etc/ssh/ssh_config on one machine:

Host *
ForwardX11 yes

And here is /etc/ssh/ssh_config on the other:

Host *
ForwardX11 yes
Protocol 2,1
StrictHostKeyChecking no

Here is verbose:

ssh -v 192.168.1.130
OpenSSH_3.6.1p2, SSH protocols 1.5/2.0, OpenSSL 0x0090702f
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Rhosts Authentication disabled, originating port will not be trusted.
debug1: Connecting to 192.168.1.130 [192.168.1.130] port 22.
debug1: connect to address 192.168.1.130 port 22: Connection timed out
ssh: connect to host 192.168.1.130 port 22: Connection timed out

I've also tried ssh -1 192.168.1.130 and ssh-2 192.168.1.130, and the reverse (from the other box to the other).

I can ssh into either linux pc from the windows pc. I can also ssh out to my remote webserver box from any one of the three pc's. The only thing I can't do is ssh from either linux box to the other. Can't understand why.

Are you ssh'ing as root? Generally only connections from regular users will be accepted.

Do you have any firewall rules that may be playing a part here?

sshing as user (rotwang).

As for firewall- if the windows pc (connected to the same linsys router) can ssh in, then the port must be open.

But I checked anyway, it's open on both boxes.

Sure, but the linux boxes might be specifically denied. Not saying they are...you just need to think of everything.

Do you have a .ssh directory in your users home directory with your keys and known hosts files? You will need to set this up for both boxes you want to ssh from.

Yes, there is a .ssh dir in the user dir on both linux pc's. (I would need this to be able to ssh out to the remote webserver, which I can do)

I've never put anything in hosts.allow or hosts.deny on either linux pc.