Group containing a network for rule filter?

We don't have any group type or field that's very subnet-aware (unfortunately) but you could build a User-Defined Group that contained each IP in the subnet and have the filter/rules use that as an exclude.

     An interesting idea... except that a /20 network contains 4094 usable host IPs. I've seen the slowdowns that can happen with a lot of entries in User-Defined Groups (see also Spyware Sites discussion in another thread) so I'm not sure if that might not create another problem...

Very old thread I know, but since I'm dealing with something similar I figured I'd add this just in case anyone else came across this when searching like I have.  Wild cards are probably a much better way than entering/importing a bunch of IP addresses into a group.  Just make a user defined group, then put in objects that represent the all the subnets you need to group together.  So here are three different examples:192.168.2.*, 10.0.*, or 172.16.3.*  Just make sure you put the wildcard after a period so that you don't get unexpected results.  Filtering a subnet like this 192.168.2* is not the same as 192.168.2.*, since the first one would catch 192.168.2.x or 192.168.2x.x or 192.168.2xx.x  Pretty obvious to some people I'm sure, but it is an easy mistake to make when adding several subnets to a group.