[Courses] [Security] safe use of nmap

[Terri Oda]

>Running nmap on localhost and running it on a different system produce
>different results ... For the record, I'm using Debian Woody on both boxes
>(upgraded from Potato in both cases). The host being scanned is running
>ipchains (kernel 2.2.17).

Note: running nmap on localhost and running it on any other valid ip of 
your system will also produce different results.  When I run nmap 127.0.0.1 
I see my mailserver listening, but since I've fixed it so that it only 
listens inside, I *don't* see it when I run nmap on 192.168.x.x (my 
internal IP for my local network.)

I was quite pleased to discover that since I went to change settings, I now 
have nothing listening externally, and only what I expect listening 
internally, according to nmap.  (At least this is true when I'm not doing 
anything)  Of course, this means my computer is pretty much useless as a 
server, but since it's *not* a server and rarely acts as one, I'm happy 
with this as my initial state after booting and starting up X. :)