Snort config questions

[comprepsrv]

Hello, when configuring various snort rules, does the 
EXTERNAL_NET variabe automatically monitor your 
external NIC or do you have to add your IP to every 
line? (same for HOME_NET).

Also, when I add my IP and test snort, I get a bad port 
error.  What is the correct way to put my IP in a line?

thanks

dp