Re: SYN flood protection strategies (Was: Post connection SYN)

[Mikael Olsson <mikael.olsson () clavister com>]

Paul Robertson wrote:
> Mikael Olsson wrote:
> > OR you set up the firewall to answer SYNs on behalf of the server
> > and wait for the handshake with the client to complete before doing
> > the handshake with the server [...]
>
> You'd still want some sort of rate limit to stop floods and broken
> clients, unless you think a ring buffer solves that probelm?  Otherwise,
> you've just moved flood protection from N servers to less than N
> firewalls, no?

I've moved the problem from servers with perhaps as low as 5 embryonic
SYN sockets per port, that block for a full minute when the list is 
full, to a firewall that can handle hundreds of thousands of states, 
embryonic or not, and knows to nuke old embryonic SYNs when the 
state table is full.

Yes, there are TCP stacks that handle SYN floods much better than
what I described above (the linux crowd will undoubtedly cheer in with
"all the world is a linux box!" here), but those that do handle it well
enough on their own simply don't need the firewall to do SYN flood 
protection for them -- right?


-- 
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
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