em0, polling performance, P4 2.8ghz FSB 800mhz
don at sandvine.com
Sun Feb 29 08:16:21 PST 2004
From: Mike Silbersack [mailto:silby at silby.com]
> On Sat, 28 Feb 2004, Don Bowman wrote:
> > You could use ipfw to limit the damage of a syn flood, e.g.
> > a keep-state rule with a limit of ~2-5 per source IP, lower the
> > timeouts, increase the hash buckets in ipfw, etc. This would
> > use a mask on src-ip of all bits.
> > something like:
> > allow tcp from any to any setup limit src-addr 2
> > this would only allow 2 concurrent TCP sessions per unique
> > source address. Depends on the syn flood you are expecting
> > to experience. You could also use dummynet to shape syn
> > traffic to a fixed level i suppose.
> Does that really help? If so, we need to optimize the syncache. :(
In a real-world situation, with some latency from the originating
syn-flood attacker, the syncache behaves fine.
In a synthetic test situation like this, with probably ~0 latency
from the initiator, the syncache gets overwhelmed too.
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