CGNAT - Seeking Real World Experience

Ca By cb.list6 at
Fri Nov 25 04:06:01 UTC 2016

On Thu, Nov 24, 2016 at 7:05 PM Adam <adamkuj at> 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

We see around 70% of traffic using ipv6 (goog, fb, netflix, ... now
cloudfront and Cloudflare ) , that takes a lot of the sting out of CGN


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