Subject: fe80::

From: "Templin, Fred L" <[email-masked]>
Date: Fri, 28 Jul 2017 14:33:04 +0000

I don't think we ever reached conclusion as to what "fe80::" is. Is it a
subnet router anycast address for the link-local prefix? Is it simply an
ordinary LL unicast address? Is it a "nothing" that should be flagged
as a bogon?

Whatever the answer, RFC4291bis should say something about it.

Thanks - Fred

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From: Mark Smith <[email-masked]>
Date: Sat, 29 Jul 2017 01:44:15 +1000

> ordinary LL unicast address? Is it a "nothing" that should be flagged

I think it is a subnet router anycast address. fe80::/64 (or perhaps
fe80::/10) is only special because it is autoconfigured on every link,
and therefore is an "anycast prefix" that happens to be present on
every link.

It is not special from the perspective of the sender. A sender to
destination fe80::(/128) would expect the "closest" on-link router to
be the one that responds, which is the one that responds to the ND NS
quickest.

I think one of the differences between IPv4 and IPv6 is that IPv4 only
inadvertently supported "off-link anycast", meaning that the
forwarding domain supported choosing the closest off-link destination,
and it was possible to announce multiple versions of that destination
into the forwarding domain, where as IPv6 supports both formal
"on-link anycast" as well as "off-link anycast".

Formal "on-link" anycast support means preferring the first rather
than the last received ND NA (indicated by the Override flag), and not
performing DAD for addresses that are flagged as anycast addresses.

> Whatever the answer, RFC4291bis should say something about it.

A reference to RFC7094, "Architectural Considerations of IP Anycast",
with a bit of referential or context setting text might do.

Regards,
Mark.

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From: "Templin, Fred L" <[email-masked]>
Date: Fri, 28 Jul 2017 16:20:14 +0000

Hi Mark,

> -----Original Message-----
> From: Mark Smith [mailto:[email-masked]]
> Sent: Friday, July 28, 2017 8:44 AM
> To: Templin, Fred L <[email-masked]>
> Cc: [email-masked]
> Subject: Re: fe80::
> 

I can live with that, but some documentation needs to say something
somewhere about fe80::/128.

Does this match with what everyone else is thinking?

Thanks - Fred