nmap weirdness?

[Michael Hipp]

I'm experimenting with a new firewall setup on one of my machines and trying 
to check it with nmap.

When I do 'nmap a.b.c.d' it says everything is closed or filtered which I know 
is wrong since I can ssh into port 22.

When I do 'nmap -p 22 a.b.c.d' it says 22 is open. True.

When I do 'nmap -p 1-100 a.b.c.d.' it says they are all filtered or closed.

Is this normal behavior for nmap?

The host doing the scanning is behind a NAT - does that matter?

Michael