RE: filtering by packet contents?

["Waldecir Loureiro dos Santos Filho" <waldecir.santos@centriabusiness.com.br>]

i have a question, how can i measure the cpu load of my linux box with
iptables ?
i have a P200 but allways stay in 98% idle and i have a High traffic going
in.
i see high traffic with TCPDUMP. heehe

somebody know how ?


-----Original Message-----
From: netfilter-admin@lists.netfilter.org
[mailto:netfilter-admin@lists.netfilter.org]On Behalf Of George Vieira
Sent: quarta-feira, 16 de julho de 2003 03:43
To: Daniel Chemko
Cc: cc; netfilter@lists.netfilter.org
Subject: RE: filtering by packet contents?


Yes this is true but what you can do is this...

Patch in the "string" module as well as the "iplimit" module

Add a rule for "iplimit" to block already registered IPsfor xx seconds.
Then add a rule for SYN connections with that --string to add it's source to
the iplimit table.

Usually the code red attacks aren't spoofed (from memory) and are just
trying to get in.. so after the first attempt, the second/third/fourth will
be automatically dropped and won't be looked at by --string since iplimit
blocks before it... get it? this should not stress the CPU as much I don't
think...

dunno if that made sense or would fully work 100% but it's an idea I had for
other types of problems.. PSD is another one..

Thanks,
____________________________________________
George Vieira
Systems Manager
georgev@citadelcomputer.com.au

Citadel Computer Systems Pty Ltd
http://www.citadelcomputer.com.au

-----Original Message-----
From: Daniel Chemko [mailto:dchemko@smgtec.com]
Sent: Wednesday, July 16, 2003 4:23 PM
To: George Vieira
Cc: cc; netfilter@lists.netfilter.org
Subject: Re: filtering by packet contents?


George Vieira wrote:

>You can you use the p-o-m patch for the string module "-m string --string
pattern"
>
>this works and can be used for some funky stuff too like redirecting 1
virtual host on a server to another server which is very handy when a
particular virtual host goes down...
>
>
>

Just keep in mind that the string patch is VERY heavy on CPU depending
on how much traffic passes through the rule.




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