Re: appropriate length of fe80:: prefix and new IP-over-foo drafts

[神明達哉 <[e-mail]>]

At Thu, 31 Jan 2019 14:00:04 +0100,
Alexandre Petrescu <[e-mail]> wrote:

> >> Ah?  according to which spec do the BSD implementers put bits in the
> >> range 16-64?
> >
> > They don't send those bits on the wire. But they do use those bits as
> > described. -- According to no spec. If the link-local prefix is assumed
> > to be /64, then you're free to use those bits *internally* as you wish.
> > That's what BSDs do. Jinmei is quite likely in a better position ot
> > comment on this.
>
> I would like to kindly ask Jinmei to make sure to keep that internal
> such that to not forbid the end user to ifconfig add fe80:1::1/63

I don't think it's up to me anymore, but just to explain the current
state of art:
- an end user of a BSD box can't use fe80:1::1 as a "link-local" address
- BSD hosts generally drop incoming packets whose source or
  destination address matches fe80::/10 and contains a non-0 value in
  bits 15-31 (like fe80:1::1)

Basically it doesn't allow an IPv6 address that matches fe80::/10
unless it conforms to following format specified in RFC4291:

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         |
   +----------+-------------------------+----------------------------+

The BSD implementation conforms to the RFC.  If someone wants to
violate the standard, they can freely do so, but they cannot assume
it's interoperable with other standard-compliant implementations.
That's a consequence of violating the standard.

I previously stated I was already done with this discussion, so I'll
stop here.  Anyone can freely hate this specification, but if it's not
even about an attempt of updating that specification (which is my
understanding of the previous cycle of this discussion), I don't think
it's a productive way of using my time to participate in it.

--
jinmei