Firewall Performance Question.

[Michael Sierchio]

Tom Daly wrote:

>>>The average firewall ruleset runs around 600-800 rules, running on IPFW.
>>
>>That's a huge number of rules -- do you have any idea what number
>>of packets are checked against how many rules before being accepted
>>or denied?  A histogram would be nice....
> 
> Most of these rules are a simple "ipfw deny all from x.x.x.x to any."
> Could some sort of source route to a null interface be better?
> 
> The base ruleset is about 160 rules. The box can handle this with minimal
> CPU load. The additional 500 rules, similar to the one above are the
> problem.

I'm of the opinion that 100 rules makes for a very large
ruleset.

> Suggestions?

So, you're incurring a huge penalty for those packets that you
allow in order to deny hosts/networks explicitly.  Why?  What
percentage of packets are denied if you let them fall through to
the bottom?


Also, I strongly urge you to switch to IPFW2 -- in addition to
using sets you can enable or disable atomically, or switch
atomically, you can do things like:

#!/bin/sh

# fw rules

bad_guys="{ \
         61.11.0.0/19 or \
         61.144.16.0/16 or \
         61.72.248.192/26 or \
         203.248.0.0/13 or \
         210.72.224.0/24 or \
         211.71.128.0/18 or \
         211.104.0.0/13 or \
         211.112.0.0/13 or \
         211.194.117.160/27 or \
         212.45.13.0/24 or \
         217.80.0.0/13 or \
         218.144.0.0/12 \

	etc.
}"

# people we simply are not at home for
ipfw add 00700 set 0 deny ip from $bad_guys to any in recv $oif

# block those Microsoft protocols
ipfw add 00900 set 0 deny ip from any to any 137-139,445,568-569,1433-1434,1512,2002 in recv $oif

You get the idea -- it's not just the expressiveness of the
notation, but the efficiency in matching packets that helps.