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Comment by majke | Hacker News Reader

Digging more about IPv6 representation:

- It's possible to stick "::" in many places

- It's possible to have :0000: before or after "::"

- leading zeros (:0001: is the same as :1:)

- "Text Representation of Special Addresses", so the ::192.168.0.1 representation

- hex uppercase vs hex lowercase

Also due to the ambiguity of ports also using a colon delimiter, the IPv6 address may be in brackets:

    [::1:2:0:0:dead:beef]:443

And link-local addresses are mandatory and scoped per interface, so they need a zone id supplied as either an integer or interface name:

    fe80::1:2:0:0:dead:beef%eth0

that rfc says upper/lower doesn't matter? Am I wrong?

That's the point: because it doesn't matter it provides two representations for the same semantic thing.

Well, that's just like IPv4, then. They can still be canonicalized, if you need to compare them.