Rate limiting, DoS

Adrian Chung
2001-06-07T17:10:44Z

Hi everyone!  Question about "rate limiting" and DoS mitigating
features of 2.4''s iptables.

With iptables, it''s possible to limit the acceptance of different
types of packets to a certain level, in order to try to mitigate DoS
attacks on the box (syn floods, ping floods, etc).

I realize that most DoS attacks happen as a result of the CPU being
unable to keep up, and not bandwidth limitations, but I''m unsure as to
why rate limiting packets works to lessen CPU processing load.

Doesn''t the kernel still have to use cycles to process the packets
before deciding to throw them out, or pass them on?  And if so, is the
cost savings in terms of CPU load just because they don''t get passed
to other system facilities which would otherwise respond and use more
CPU cycles?

Or does this make any sense? :)

--
Adrian Chung (adrian at enfusion-group dot com)
http://www.enfusion-group.com/~adrian
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