Yes, from one NAT IP using the same protocol to a single public IP using a particular port. Change any of those and you can do 2^16 concurrent connections more per change.
In other words, NAT works on the five-tuple of: protocol, source IP, source port, destination IP and destination port.
> What did we read right here on HN recently about IP blocks changing hands for about $40 per address? IPv6 addresses are approximately 100% cheaper than that.
This is just silly. If you are an ISP then you already have an IPv4 allocation.
If you don’t then you join the waiting list and/or apply for a /24.
Once you have your allocation, RIR fees are the same regardless of IPv4 or IPv6 allocations.
> But it doesn't stop there, you also no longer need subnet planning -- where under IPv4 it's very important whether this new subnet is 60 machines or 64 machines, in IPv6 you don't care and so nobody needs to manage that. Which translates to lower costs in your network team. Negligible when your "network team" is just the CTO doing a Google search, but significant at scale.
If you believe this is in any way meaningful then I have a bridge to sell you.
> Your route costs fall too. Because of exhaustion (and because years ago nobody had any idea what they were doing, not having had an Internet before) IPv4 is now badly fragmented, which means a trivial route ("All the East Coast stuff") may become six or sixteen or sixty separate address blocks, but IPv6 blocks were deliberately assigned so as to reduce fragmentation, chances are "All the East Coast stuff" is one or two blocks.
You can’t buy smaller routers just because you deploy IPv6, so I have no idea what cost saving there are to be had here.
> As to speed, Facebook reports IPv6 is about 10% faster for them.
I fail to see how this is universally applicable to all ISPs.
> They did exactly what I described, they're v6-only internally and have translation at the edge for "legacy" IPv4 clients.
Having an IPv6 core is not the same thing as being IPv6-only.
Speaking of IPv6-only, you have yet to name even a single ISP that is even considering going IPv6-only. Cat got your tongue?
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?
IPv6 “just works” only if you completely control the routing stack end-to-end.
Once end user equipment and hosts are introduced into the network all bets are off.
In a mobile network, where the carrier controls what user terminals are allowed on the network, it is at least nominally possible to achieve “just works” status.
So, in the real world, forcing IPv6 would result in IPv6 being supported only in a particular configuration used in a particular way. Everybody will be told to go pound sand and no effort will be made to keep IPv6 working or prevent breakage.
You assume new entrants or smaller entities would have a fighting chance in this scenario. They would not.
The incumbents would become king makers. They would decide which services would be allowed on the IPv4 Internet, which would be the only Internet, and which services would be allowed to prosper.
The incumbents would either acquire all successful startups and smaller companies or clone their services.
New entrants would wither on the wine on this obscure IPv6-only network that hardly anybody knows about or is able to access.
This would also kill off IPv6 completely. The incumbents would have a collective interest in maintaining and propping up their position. IPv6 would be a threat to this, so it would be given the axe.
This isn’t some far out fantasy either. This is how mobile phone services worked during the SMS era before the Internet was a thing.
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.