NAT444 or ?

Leigh Porter leigh.porter at ukbroadband.com
Wed Sep 7 15:05:08 CDT 2011



> -----Original Message-----
> From: Seth Mos [mailto:seth.mos at dds.nl]
> Sent: 07 September 2011 20:26
> To: NANOG
> Subject: Re: NAT444 or ?
> 
> I think you have the numbers off, he started with 1000 users sharing
> the same IP, since you can only do 62k sessions or so and with a
> "normal" timeout on those sessions you ran into issues quickly.
> 
> The summary is that with anything less then 20 tcp sessions per user
> simultaneous google maps or earth was problematic. From 15 and
> downwards almost unsable.
> 
> He deducted from testing that about 10 users per IP was a more
> realistic limit without taking out the entire CGN "experience".
> 
> On a personal note, this isn't even taking into question things like
> broken virus scanners or other software updates that will happily try
> to do 5 sessions per second, or a msn client lost trying to do 10 per
> second. The most the windows IP stack will allow on client versions.
> 
> The real big issue that will be the downfall of NAT444 is the issue
> with ACLS and automatic blocklists and the loss of granular access
> control on that which the ISP has no control of. Which roughly
> estimates to the internet.
> 
> Regards,
> 
> Seth

I was thinking of an average of around 100 sessions per user for working out how things scale to start with. It would also be handy to be able to apply sensible limits to new sessions, say limit the number of sessions to a single destination IP address and apply an overall session limit of perhaps 200 sessions per source IP address.

ACLs and blocklists are going to be a problem, perhaps, as LSN becomes more and more common, such things will gradually die out.

Considering that offices, schools etc regularly have far more than 10 users per IP, I think this limit is a little low. I've happily had around 300 per public IP address on a large WiFi network, granted these are all different kinds of users, it is just something that operational experience will have to demonstrate.

I would love to avoid NAT444, I do not see a viable way around it at the moment. Unless the Department of Work and Pensions release their /8 that is ;-)


--
Leigh


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