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