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Date:      Thu, 13 Nov 2003 13:54:33 +0100
From:      Anders Lowinger <anders@lowinger.se>
To:        Haesu <haesu@towardex.com>
Cc:        freebsd-net@freebsd.org
Subject:   Re: tcp hostcache and ip fastforward for review
Message-ID:  <3FB37F09.4050908@lowinger.se>
In-Reply-To: <20031112195529.GA48020@scylla.towardex.com>
References:  <20031112024507.89398.qmail@web10007.mail.yahoo.com> <3FB20D2B.73624906@pipeline.ch> <20031112195529.GA48020@scylla.towardex.com>

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Haesu wrote:
> I agree in that flow cache is bad and it should not be used.

Everything is not black or white.

A flow cache can accelerate for example Access Control Lists
and/or firewalling, since only the first packet needs to be
verified.

Cisco just added ACL bypass for firewall, which is a similar feature.
http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_feature_guide09186a00801d33da.html

> It only takes x num. of kpps with diverse destinations to knock off a router running flow based caching.

Yep, that is true and its hard to work around.

> Extreme switches use flow based caching (called ipfdb) and any DoS attack that uses
> diverse destinations will kill it pretty quickly..

Cisco's newer stuff does the flow-cache independent of the forwarding, i.e. the
flow is more of an accounting cache.

--Anders, not affiliated with Cisco



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