Firewall Wizards mailing list archives
Re: Inspecting routers
From: Mikael Olsson <mikael.olsson () clavister com>
Date: Mon, 25 Nov 2002 23:39:59 +0100
Hullo, I've got some disagreeing to do ... Lorens Kockum wrote:
It will, on the other hand, cost you. Stateful filtering is more expensive than non-stateful in terms of CPU / memory / performance.
... here. Stateful filtering is indeed more expensive in terms of memory. It _might_ be more expensive if what you are doing is adding and removing real rules to/from the ruleset a'la cisco router reflexive ACLs (but I thought people stopped doing that after nimda killed their routers; maybe I'm wrong :P) IF however you are using a firewall built expressly for SPFing, you'll find that it's LESS expensive in terms of CPU crunching and perform better. Think about it; a state lookup can be done with a single hash lookup on primitive data types. A (linear) ruleset lookup will result in lookups against (typically) more complex datatypes, one for each and every rule you look at. That said, one _can_ get fancy on the rule lookup algorithm itself and get it done in more-or-less constant time, but that still only puts things more or less on par with the speed of the state lookup, and with none of the benefits that you can get from keeping state. -- Mikael Olsson, Clavister AB Storgatan 12, Box 393, SE-891 28 ÖRNSKÖLDSVIK, Sweden Phone: +46 (0)660 29 92 00 Mobile: +46 (0)70 26 222 05 Fax: +46 (0)660 122 50 WWW: http://www.clavister.com _______________________________________________ firewall-wizards mailing list firewall-wizards () honor icsalabs com http://honor.icsalabs.com/mailman/listinfo/firewall-wizards
Current thread:
- Inspecting routers Pierre-Yves (Nov 25)
- Re: Inspecting routers Lorens Kockum (Nov 25)
- Re: Inspecting routers Mikael Olsson (Nov 25)
- Re: Inspecting routers Kyle R. Hofmann (Nov 25)
- Re: Inspecting routers Lorens Kockum (Nov 26)
- Re: Inspecting routers Ng Pheng Siong (Nov 26)
- RE: Inspecting routers Ben Nagy (Nov 26)
- Re: Inspecting routers Lorens Kockum (Nov 25)