Define "anycast address" in this question?
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.
I didn't see the draft, but I was talking with Eric Nordmark about a notion I have that IP Mobility would be very useful in anycast services, and he told me that he had actually described it a year earlier. OK, so it's his proposal... Anycast works pretty well with DNS, and presumably with similar services that do not set up long tem associations. But with anything that routinely opens a TCP session, the use of anycast exposes the user to a problem when routing changes sufficiently to change servers. All of a sudden he's talking to someone who has no idea what he's talking about. The simple solution is to use Optimized Routing - connect to the AnyCast address, obtain the fixed address of the server as a Care-of Address, and then talk with the care-of address. You get the "nearest" server, a benefit of anycast, and then get to talk with it reliably even if routing changes. The big problem with this is that one has to open an IPSEC association with the anycast address, which this rule precludes.
I think that there is a good operational reason to allow for that model, which means that one really does need to be able to use the anycast address a a source just long enough to obtain the care-of address. I think it would be good for the document to describe the scenario and impose appropriate limits (you don't talk all day to the anycast address, you only use it to find the peer and get a better address for him), but it should allow for the scenario.
On Apr 6, 2005, at 10:22 AM, Brian Haberman wrote:
All, I am soliciting input on a proposal to modify the rules defined in the current addressing architecture draft with respect to anycast. There is a proposal in draft-jabley-v6-anycast-clarify-00.txt to change the following text in the addressing architecture:
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.
to
o An anycast address MAY be used as the source address of an IPv6 packet. o An anycast address MAY be assigned to an IPv6 host.
This change will allow users to operate IPv6 anycast services in the same
manner in which they do today with IPv4 anycast.
I would like people to chime in before April 15, 2005 with their opinion on
making this change.
It should be noted that the addressing architecture is currently in IETF Last
Call.
Regards,
Brian------------------------------------------------------------------ --
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