The SSH configuration file is called /etc/ssh/sshd_config. By default SSH listens on all your NICs and uses TCP port 22. Take a look at a snippet from configuration:
# The strategy used for options in the default sshd_config shipped
with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented. Uncommented options change a
# default value.
#Port 22
#Protocol 2,1
#ListenAddress 0.0.0.0
#ListenAddress ::
SSH Versions 1 and 2
The original encryption scheme of SSH was adequate for its time but was eventually found to have a number of limitations. The answer to these was version 2. Always force your systems to operate exclusively with version 2 by setting the protocol statement in the /etc/ssh/sshd_config file to 2. Remember to restart SSH to make this take effect.
#
# File: /etc/ssh/sshd_config
#
Protocol 2
Change the TCP Port on Which SSH Listens
If you are afraid of people trying to hack in on a well known TCP port, then you can change port 22 to a location that won't interfere with other applications on your system, such as port 435. This is a rudimentary precaution only, because good network scanning programs can detect SSH running on alternative ports.
What you need to do is:
1.
Use the netstat command to make sure your system isn't listening on port 435, using grep to filter out everything that doesn't have the string "435":
No response allows us to proceed. Change the Port line in /etc/ssh/sshd_config to mention 435 and remove the # at the beginning of the line. If port 435 is being used, pick another port and try again: Port 435
