IPv4 and CGNAT costs scale with usage. The more traffic you offload to IPv6, the less CGNAT capacity you need and the less IPv4 space you need; you need enough IPv4 addresses so you can give out unique IP:Ports for all concurrent connections to popular destination IP:Ports.

None of those are arguments for why IPv4 or CGNAT costs are optional; you cannot run an ISP without IPv4 or CGNAT, therefore the IPv4 or CGNAT costs are not optional. You will incur them regardless of if you deploy IPv6 or not.

If you deploy IPv6, you might not deploy CGNAT, but unless you are dual stacking, something functionally equivalent is required.

As to scaling costs, IPv6 offload isn’t a 1:1 replacement for IPv4 or CGNAT capacity. You need enough capacity to carry the IPv6 traffic over IPv4 in case your IPv6 transport, transit or peers fail. Again, not optional.

Parent commenter wasn't saying that CG NAT costs could be avoided entirely. Deploying IPv6 gets Netflix, YouTube, Facebook and other popular traffic to connect directly. That means less racks of CG NAT.

Like I said, you can only avoid CGNAT costs if you accept the failure modes inherent if/when your IPv6 fails.

Thus in a properly designed network these are not optional costs.

You do avoid some of the cost, because you can direct a significant amount of your traffic over v6 and not need to CGNAT it.

The failure mode for your v6 failing is the same as it is for v4 failing in a v4-only ISP: stuff breaks. If you want to fix that you need a redundant failover setup, which is the same thing you need in v4 except cheaper because it doesn't need to do CGNAT.

> You need enough capacity to carry the IPv6 traffic over IPv4 in case your IPv6 transport, transit or peers fail. Again, not optional.

Surely you need enough IPv6 capacity incase your IPv4 transit fails as well. If JIO could have built enough IPv4 capacity to run their network over IPv4, they would have, but they can't, so they've been pushing IPv6 hard.

You are likely to be unable to source the missing IPv4 traffic over IPv6.

I’m not familiar with JIO’s setup, but that’s an interesting question. If their IPv6 was down, would their network still be able to deliver? Would they run out of CGNAT capacity or IPv4 translations?

If their IPv6 failed, they would almost certainly run with significant service disruption.

IPv6 is no longer optional for them. I suspect it's not optional for T-Mobile USA either. Or Facebook/Google/Netflix.

Don’t think IPv4 is optional for any of them either.

Less racks of CG NAT. Deploying IPv6 gets Netflix, YouTube, Facebook and other popular traffic to connect directly.