CGNAT - Seeking Real World Experience

Stepan Kucherenko twh at
Fri Nov 25 08:18:55 UTC 2016

Don't try detereministic NAT, it's not worth it. You'll waste a lot of 
port capacity on most users, and it might still be problematic for power 

Just try to match one user to one real IP, many sites/applications don't 
like when there are several requests from one user with different IPs. 
After that just stack as many users on one IP as you can and that's it. 
It's the only way CGN can be worth the trouble.

If you really need to know who was using which port, just log them and 
correlate them when/if the need arises.

On 24.11.2016 00:17, Adam wrote:
> I'm crunching the numbers on the cost effectiveness of implementing CGN vs
> IPv4 auctions. The determining factor is how many ephemeral ports are
> reserved for each customer. This is for a residential broadband environment.
> Is anybody doing deterministic NAT/PAT (i.e. each customer gets X ports -
> no more, no less)? My thinking is that X=8192 would cover even the power
> users. However, with only 8 customers per public IPv4 address, CGN is not
> worth the trouble. With X=8192, our money and time would better be spent
> acquiring additional IPv4 space. Are people successfully using a smaller
> deterministic port allocation? What's your X?
> If I can't make the numbers work for deterministic NAT, I might be able to
> live with dynamic port assignments. Specifically, I'm referring to what
> vendor J calls "Port Block Allocation". I was thinking 1024 ports per
> block, with up to 8 blocks per customer (and a bunch of log correlation to
> determine who was using which ip:port tuple at a given datetime). I *can*
> make the math work out in favor of CGN if the average customer uses <= 3072
> ports (3 blocks). But is that going to be enough? I'd love to hear other
> people's experiences.
> Thanks!
> -Adam

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