IPv6 woes - RFC

Wed Sep 22 19:45:47 UTC 2021

On Wed, 22 Sept 2021 at 16:48, Masataka Ohta <
mohta at necom830.hpcl.titech.ac.jp> wrote:

> Today, as /24 can afford hundreds of thousands of subscribers
> by NAT, only very large retail ISPs need more than one
> announcement for IPv4.
>

You can only have about 200-300 subscribers per IPv4 address on a CGN. If
you try to go further than that, for example by using symmetric NAT, you
will increase the number of customers that want to get a public IPv4 of
their own. That will actually decrease the combined efficiency and cause
you to need more, not less, IPv4 addresses.

Without checking our numbers, I believe we have at least 10% of the
customers that are paying for a public IPv4 to escape our CGN. This means a
/24 will only be enough for about 2500 customers maximum. The "nat
escapers" drown out the efficiency of the NAT pool.

The optimization you need to do is to make the CGN as customer friendly as
possible instead of trying to squeeze the maximum customers per CGN IPv4
address.

Perhaps IPv6 can lower the number of people that need to escape IPv4 nat.
If it helps just a little bit, that alone will make implementing IPv6 worth
it for smaller emerging operators. Buying IPv4 has become very expensive.
Yes you can profit from selling a public IPv4 address to the customer, but
there is also the risk that the customer just goes to the incumbent, which
has old large pools of IPv4 and provides it for free.

Regards,

Baldur
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