"fe80:6666:6666:6666:6666:6666:6666:6666" is not a valid IPv6 link-local address

[lbaumbauer]

Bug description:

>>> import ipaddress
>>> ipaddress.IPv6Address("fe80:6666:6666:6666:6666:6666:6666:6666").is_link_local
True

The spec says there must be 54 bits of zero.
the address must be within fe80::/64, not merely within fe80::/10.
2.5.6. Link-Local IPv6 Unicast Addresses

 Link-Local addresses are for use on a single link. Link-Local
 addresses have the following format:

 | 10 |
 | bits | 54 bits | 64 bits |
 +----------+-------------------------+----------------------------+
 |1111111010| 0 | interface ID |
 +----------+-------------------------+----------------------------+

CPython versions tested on:

3.13

Operating systems tested on:

No response

Linked PRs

• gh-155140: Fix ipaddress.IPv6Address.is_link_local to require the strict fe80::/64 range #155384

[BHUVANSH855]

I took a look at the current implementation, and is_link_local is simply checking membership in fe80::/10, which is also what the existing test suite expects.

Changing this to /64 fixes the reported example, but it also changes long-standing behavior and causes the current tests to fail. Before opening a PR, it would be good to confirm whether is_link_local is intended to follow the fe80::/10 prefix or the stricter fe80::/64 address format from RFC 4291.

[Sudeep-A-Kulkarni]

Hi, I'd like to take a look at this issue. Based on the discussion above, I'll investigate whether is_link_local should follow the stricter fe80::/64 format per RFC 4291, and update the implementation and tests accordingly. I'll open a PR once I have a fix ready.