Re: Generic anycast addresses...

[Ted Lemon <[e-mail]>]

On Jul 12, 2019, at 8:14 AM, Bob Hinden <[e-mail]> wrote:
>   Anycast addresses are allocated from the unicast address space, using
>   any of the defined unicast address formats.  Thus, anycast addresses
>   are syntactically indistinguishable from unicast addresses.  When a
>   unicast address is assigned to more than one interface, thus turning
>   it into an anycast address, the nodes to which the address is
>   assigned must be explicitly configured to know that it is an anycast
>   address.

Sorry, the distinction here is that we’re talking about well-known anycast addresses being used for resource discovery or edge probing, not anycast addresses generally.

So yes, of course anycast addresses can just be unicast addresses, and can come either from an org’s delegated prefix or from a global IANA prefix.   However, this isn’t always what we want; in the case of SRP, it’s better if it doesn’t leave the site, for example, so a unique local address would be a better choice than something in 2001::/16.   But we don’t have a mechanism for allocating well-known anycast addresses out of the unique local address space.