And to further explain, here is why sshd does this:
Code:
[/var/log/auth]# grep POSSIBLE /var/log/auth/auth.log | head
Apr 15 01:30:07 cthulhu sshd[74815]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:30:11 cthulhu sshd[74862]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:30:15 cthulhu sshd[74889]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:30:50 cthulhu sshd[74958]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:30:56 cthulhu sshd[75000]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:31:00 cthulhu sshd[75002]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:31:23 cthulhu sshd[75077]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:31:25 cthulhu sshd[75131]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:31:51 cthulhu sshd[75173]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Apr 15 01:32:05 cthulhu sshd[75261]: Address 190.77.95.141 maps to 190-77-95-141.dyn.dsl.cantv.net, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!