Are you using any IP filtering or access control (iptables or tcp wrappers)?
If you don't know the answer, then post the results of
# iptables -nvL (in code tags).
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edit: If you want to lock down sshd, instead of playing games with port numbers, do the following...
First set these directives in /etc/ssh/sshd_config:
- Protocol 2
- PermitRootLogin no
Next, learn about enabling pubkey authentication and disabling all other authentication forms.
Keep openssh up to date as security fixes are released.
