Can't get in without a password

[Pierre Abbat]

I have access to three machines:
A: Mandrake 7.0, OpenSSH 2.1.1.
B: Mandrake 5.3, SSH 1.2.27.
C: Mandrake 6.1, OpenSSH 2.1.1.

I can get from A to B, or B to A, without a password, but I cannot get from A
or B to C without a password. sshd_config is identical on A and C. My public
key is in authorized_keys on C, and all files in .ssh and .ssh itself have mode
600 and 700 respectively.

C is behind a port-forwarding firewall. Would that make any difference?

phma