Re: [GD-General] NAT Negotiation

[J C L. <cl...@ka...>]

On Tue, 13 Jan 2004 07:30:58 +0800 
Brett Bibby <res...@ga...> wrote:

> I believe some NATs will increment port numbers and that would be a
> good guess to try, but I also read that they may assign random port
> numbers. Seems pretty hard to establish a connection to a NAT device
> randomly generating port numbers. Hmmm...

Every cheap consumer grade low margin NAT box I've examined (roughly a
dozen) has used a base algorithm of simply incrementing the last
allocated port.  Some of them tweak this by periodically/variously
stuffing old reclaimed ports back in the available list or some other
port recycling pattern, but that's the exception rather than the rule,
and a simple retry reduces it to pretty near a 0% margin.

Higher end NAT boxes however have all sorts of tricks and behaviours.
They allocate seemingly randomly, or with ports as members of a hash
function of the address, or some other curiosity, usually in the name of
scalability or performance.  Some low end boxes do this as well (and no,
I can't quote as I'm a long way from home and my files right now), but
it isn't common at the lower ends.

-- 
J C Lawrence
---------(*)                Satan, oscillate my metallic sonatas.
cl...@ka...               He lived as a devil, eh?
http://www.kanga.nu/~claw/  Evil is a name of a foeman, as I live.