services on subnet-router anycast address?

Brian E Carpenter brian.e.carpenter at
Thu Apr 26 09:35:03 CEST 2012


On 2012-04-26 00:57, Erik Kline wrote:
> On 26 April 2012 06:35, Sergei Lissianoi <sergeilissianoi at> wrote:
>>> Lutz: Why do you think this was a subject-router anycast address?
>> It fits the definition in RFC 4291, Section 2.6.1. Required Anycast Address
> Probably we need a document in the IETF that clarifies that IPv6
> specifications involving ascribing addresses with link-specific
> properties, including but not limited to:
>     [1] subnet-router anycast
>     [2] general subnet anycast addresses a la rfc2526
>     [3] the whole U and L bit mess

The U bit is by definition not a link-specific bit; it's
explicitly an assertion that the IID is globally unique.
So I don't see what it has to do with "link-specific"
properties. By definition, it applies everywhere. I'm not
clear what the mess is.

You could propose changing the addressing architecture to
abolish the special nature of the U bit, but that is a
completely separate question.

> are recommendations specifically to the operators of the logical
> administrative domain in which that link resides (or to the group of
> operators if responsibility for a given link is shared by more than
> one administrative domain) ONLY, and that link-specific properties
> CANNOT reasonably be inferred by entities outside the responsible
> operational domain(s).

I don't think that's the point, is it? The point is that since these
are globally defined anycast addresses, any host on any subnet can
assume they exist and can construct them simply by knowing the
subnet prefix. That either applies globally (as today) or applies
nowhere (if we abolish them).

As for the original question, I'm still looking for the harm, and
I can't see any harm in having services on the RFC 2526 addresses


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