> > > An IPv6 anycast address is indistinguishable from an IPv6 unicast
> > > address. As such, any rule prohibiting the use of an anycast address
> > > in any location is unenforceable - I have no way to identify an
> > > anycast address to apply the rule.
> >
> > Correct. However, the v6 addressing spec prohibits the use of an
> > anycast address from being used as the source address in a datagram, or
> > being bound to an interface on a host. These two restrictions
> > effectively prohibit the use of anycast as a service distribution
> > mechanism.
> >
>
> Why was this prohibition was put into the specification?
>
> jak
The prohibition was put in as we didn't know how to do anycast
correctly for all cases. How to do the route injection etc.
For single packet transactions (one packet each way) as long as
you don't source the first packet from a anycast address there
is no problems with sending the reply from the anycast address.
DNS/UDP falls into this space.
For sessions bigger than this there are going to be issues that
need to be examined and maybe addressed.
e.g.
* per pack load balancing which causes traffic to go to different
anycast nodes.
* routing table changes which change the anycast node.
DNS/TCP w/ anycast assumes the first of these to be almost
non-exisitant and the second to be a non-issue as the
sessions have short life times. Again this is with the
server on the anycast address and the client on the unicast
address.
Note the important thing here is that the session (not
packet) originated from a unicast address. Replying with
unicast source address is reasonable in some/all cirumstances.
I suspect that the one of the bigger issues will be PPLB
which may require routing protocols to be able to tag
prefixes as containing anycast addresses to turn off
non-parrallel path PPLB. This tag may or may not need to
be exported across AS boundaries.
Mark
> --------------------------------------------------------------------
> IETF IPv6 working group mailing list
> [email protected]
> Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
> --------------------------------------------------------------------
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [EMAIL PROTECTED]
--------------------------------------------------------------------
IETF IPv6 working group mailing list
[email protected]
Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------
