netdev - Re: ipv4: Simplify ARP hash function.

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Message-Id: <20110708.125912.1535057393082512441.davem@davemloft.net>
Date:	Fri, 08 Jul 2011 12:59:12 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mirqus@...il.com
Cc:	roland@...estorage.com, johnwheffner@...il.com, mj@....cz,
	netdev@...r.kernel.org
Subject: Re: ipv4: Simplify ARP hash function.

From: David Miller <davem@...emloft.net>
Date: Fri, 08 Jul 2011 12:51:18 -0700 (PDT)

> From: Micha┅ Miros┅aw <mirqus@...il.com>
> Date: Fri, 8 Jul 2011 21:39:18 +0200
> 
>> With b[3] = b[0] ^ b[1] ^ b[2] you get 2^24 keys that hash to the same bucket.
> 
> Ok, I'm convinced, thanks :-)

Although, actually it's not this simple.  The attack doesn't work.

As they "attack" us, the ARP hash table grows and thus the hash mask
changes to match.  Then his old collisions won't collide any more.

We could even adjust the fold shifts as the table grows to make this
effect even more pronounced.
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