--- On Tue, 9/27/11, Tomoyuki Sahara <[email protected]> wrote:
> From: Tomoyuki Sahara <[email protected]>
> Subject: Re: Question about RFC 3484
> To: "François-Xavier Le Bail" <[email protected]>
> Cc: [email protected]
> Date: Tuesday, September 27, 2011, 8:28 PM
> Hi,
>
> > Section 4 of RFC 3484 states:
> > (http://tools.ietf.org/html/rfc3484#section-4)
> > 4. Candidate Source Addresses
> > [. . .]
> > In any case, anycast addresses, multicast
> addresses, and the
> > unspecified address MUST NOT be included
> in a candidate set.
>
> I don't know the exact reason but RFC2373[1] says:
>
> 2.6 Anycast Addresses
> ...
> There is little experience with
> widespread, arbitrary use of internet
> anycast addresses, and some known
> complications and hazards when
> using them in their full generality
> [ANYCST]. Until more experience
> has been gained and solutions agreed upon
> for those problems, the
> following restrictions are imposed on
> IPv6 anycast addresses:
>
> o An anycast address must not be used
> as the source address of an
> IPv6 packet.
>
> o An anycast address must not be
> assigned to an IPv6 host, that
> is, it may be assigned to an
> IPv6 router only.
>
> (Note: statement above was removed in RFC4291)
>
>
> Thanks,
> Tomoyuki Sahara
Hi,
RFC 4291, appendix B states:
Appendix B: Changes from RFC 3513
The following changes were made from RFC 3513, "IP Version 6
Addressing Architecture":
o The restrictions on using IPv6 anycast addresses were removed
because there is now sufficient experience with the use of anycast
addresses, the issues are not specific to IPv6, and the GROW
working group is working in this area.
In this draft, we have a rationale for the remove of restictions regarding
anycast as source address :
(http://tools.ietf.org/html/draft-jabley-v6-anycast-clarify-00#section-3.1)
"3.1 Anycast Source Addresses
For many conventional services to be distributed using anycast, it is
necessary for reply datagrams sent from servers to clients to be
sourced from the same address that was used as the destination in
request datagrams sent from clients to servers. When such a service
is distributed using anycast, the destination address used in request
datagrams is necessarily an anycast address; corresponding reply
packets must therefore use the same anycast address as their source
address.
Being able to use an anycast address as the source address in an IPv6
datagram is a prerequisite for the distribution of many services
using anycast over IPv6."
So, if the RFC 3484, Section 4 "Candidate Source Addresses" is involved in
the reply to datagrams sent to an anycast address, it might be useful to
reassess the restrictions that excluded an anycast address from the "candidate
set", at least for the replies.
François-Xavier Le Bail
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