On Sep 25, 2021, at 14:20 , Baldur Norddahl <baldur.norddahl@gmail.com> wrote:

On Sat, 25 Sept 2021 at 21:26, Owen DeLong via NANOG <nanog@nanog.org> wrote:

So the fact that:

        2001:db8:0:1::5
        2001:db8::1:0:0:0:5

Are two different ways of representing the same address isn’t
of any concern unless you’re making the mistake of trying to
string wise compare them in their text-representation format.
Both equate to the same uint128_t value.

If you adhere to RFC 5952 only the former is to be used (2001:db8:0:1::5). Also strict RFC 5952 on any output will make a string compare ok because there is only one way to print any address.

We should remember there are also multiple ways to print IPv4 addresses. You can zero extend the addresses and on some ancient systems you could also use the integer value. 

You can even encounter IPv4 printed as IPv6 which is not too uncommon. Many programs internally are IPv6 only and IPv4 is therefore mapped to IPv6. It appears some people are forgetting this fact when proposing to drop IPv6.