Dear Dmitry,

30 Jun 21 23:17, you wrote to me:

 DP>>> NAT66 is what NAT for ipv6 is called.

 VS>> What was the incentive to create such an abomination?

 DP> "There are more things in heaven and earth, Horatio,
 DP> Than are dreamt of in your philosophy."(c)Shakespeare

 DP> And original ipv6 was just a miserable philosophy, created by people
 DP> with limited knowledge about real life.

The original IPv4 was also miserable with its classful networks, RIPv1 etc. I still cannot imagine however what "real life" problem they are solving by creating NAT for ipv6.

 DP>>> NPTv6 is not a NAT, it's
 DP>>> stateless solution.

 VS>> Even if NPT is called "prefix translation" and is stateless, it
 VS>> is still a NAT (in IPv4 terms, a type of a one-to-one NAT).

 DP> NPTv6 is for prefix translation only, not for address translation.
 DP> It's much more lightweight and easy to implement.

Either you translate only the higher 64 bits of the address, or the whole 128 bits of the address, you still rewrite the packet. True, you don't do PAT, that's why I said that it looks like a one-to-one IPv4 NAT (much like in AWS VPC "public" subnets).

 VS>> However, the creators of IPv6 had better invent something like
 VS>> "dead gateway detection" or some other way for end devices to
 VS>> select a working outgoing address when they have several global
 VS>> prefixes (and gateways) available. I thought my knowledge was
 VS>> lacking, but it turns out the new and flashy protocol stack is
 VS>> lacking.

 DP> Do you have a time machine to send some ideas to ipv6 creators? :)

Nope, but I think $subj can be implemented today, e.g. via some field in RAs etc. In FreeBSD (and I'm sure in other IPv6 implementations) you can select the prerred source address, you only have to add some way to change it automatically when a "dead gateway" is detected.

Victor Sudakov, VAS4-RIPE, VAS47-RIPN
--- GoldED+/BSD 1.1.5-b20170303-b20170303