Sshd Configuration

Internal

• ssh

Change the Default Port

Uncomment and/or update the default "Port" value in /etc/ssh/sshd_config:

#Port 22
Port 12345

Change the Default Port on a SELinux System

If SELinux is enable, you have to tell SELinux about the port change:

semanage port -a -t ssh_port_t -p tcp 12345

Also see How to install SELinux semanage.

Update the Firewall Rules

If iptables is enabled, there's a firewall rule that allows ssh access, and it usually mentions the port. You may want to check and change that: Iptables_Command_Line_Tool_Examples#Allow_SSH_Only_From_the_Internal_Network_on_a_Non-Standard_Port

Turn off Client Name DNS Verification

sshd can be configured with a "UseDNS" option, which specifies whether sshd should look up the remote host name and check that the resolved host name for the remote IP address maps back to the same IP address. The default is “yes” but in some case this causes the initial connection setup to take a long time, so it is best to turn this verification off:

...
UseDNS no
...