Re: Question on anycast IID range(s)

[David Farmer <[e-mail]>]

Comments inline;

On Sat, Jan 5, 2019 at 3:45 PM Brian E Carpenter <
[e-mail]> wrote:

> A comment right at the end:
>
> On 2019-01-06 09:41, Ole Troan wrote:
>
> >> Do we know the deployment / implementation status of the reserved
> anycast space?
> >> And how costly it would be to restate the reserved state as top-most
> 128 addresses, and not carry with us the U/G bits?
> >>
> >> I do not have direct knowledge, but I'm thinking about the possible
> impact on
> >> current Mobile IPv6 implementations.  RFC3775  defines functionality of
> the mobile
> >> node, e.g. "The mobile node sends the Home Agent Discovery Request
> message to
> >> the Mobile IPv6 Home-Agents anycast address ... for its own subnet
> prefix", and of
> >> the home agent, e.g. "Every home agent MUST be able to accept packets
> addressed
> >> to the Mobile IPv6 Home-Agents anycast address ... for the subnet on
> which it is
> >> serving as a home agent …"
> >
> > Doesn’t the mobile agent already need to know the type of home-link, if
> it is on a link-type using modified EUI-64 (and it’s prefix length)?
>

To be safe, if I were implementing a Moblie node I would probably try both
anycast addresses [Home subnet]:ffff:ffff:ffff:ff7e and [Home
subnet]:fdff:ffff:ffff:ff7e, and if implementing a Home-Agent I would
probably bind to both addresses as well. But, I have no idea what
implementations actually do.


> >> If we now recommend the range of IID values ffff:ffff:ffff:ff80-ff,
> would existing Mobile
> >> IPv6 implementations need to be modified to send to or receive from the
> reserved
> >> Mobile IPv6 Home-Agents anycast address in both the new and legacy
> ranges?  I
> >> agree that it is not the most elegant solution to retain just the
> current fdff:ffff:ffff:ff80-ff
> >> range (along with revising RFC2526), but it may be the least disruptive.
>

You seem to assume Moblie IP implementation are using fdff:ffff:ffff:ff7e,
if they are then your assumption about what is easier holds, but if any
Moblie IP implementations use ffff:ffff:ffff:ff7e then your assumption
doesn't hold.


> > I must admit I’m quite attracted to the simplicity of:
> > "The subnet anycast address range is the top-most 128 addresses on any
> link with prefix length <= 120."
>

+1


> Yes, but in that case the fdff: range was an error from the beginning
> (compounding what I always thought was an error: the inversion of the IEEE
> "u" bit). If not an error, it was in any case an exception to the "top-most
> 128" rule.
>

+1

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