Reverse Mapping Checking - Possible Break-in Attempt Error with SSH

Reverse DNS not set up

Connecting from the command line, you might enter something like this:

1	ssh my.example.com

and get some output like this:

1	Connecting to my.example.com...

2	reverse mapping checking getaddrinfo for 192-168-1-243.foo.bar.net failed - POSSIBLE BREAK-IN ATTEMPT!

3	chris@my.example.com's password:

What this is telling us is that although we are connecting to my.example.com the IP address of the server we are connecting to actually maps back to 192-168-1-243.foo.bar.net in this example. When this actually happened to me, it's because the reverse DNS had not been set up for the server (which would map e.g. 192.168.1.243 to my.example.com as well as vice versa).

Hosts file solution

Because I knew this reverse mapping was OK, I can add an entry to my hosts file and it will stop the error message from happening. For the above example, I would add the following to my hosts file:

1	192.168.1.243  my.example.com