----- Original Message -----
> From: Bob Hinden <bob.hin...@gmail.com>
> To: Randy Bush <ra...@psg.com>
> Cc: "ipv6@ietf.org List" <ipv6@ietf.org>; Bob Hinden <bob.hin...@gmail.com>
> Sent: Friday, 21 December 2012 1:47 AM
> Subject: Re: IIDs, u and g bits, and 4rd
>
> Randy,
>
> On Dec 20, 2012, at 3:02 PM, Randy Bush wrote:
>
>>>> "The IID consists of N bits that have no meaning; the only
> constraint
>>>
>>> Hmm.. how would this work with RFC5453 reserved IID space we already
>>> have for anycast addresses?
>>
>> is anyone aware of any deployment of the ipv6 invented anycast?
>>
>> like most ipv6 magic, i think it is ignored and regular old ipv4-style
>> anycast is used.
>
> I assume you mean the subnet-anycast addresses (i.e., Subnet-Router anycast
> address). IPv6 has always had what you call regular old ipv4-style anycast.
> See section 2.6 of RFC4291.
>
The other difference is that IPv6 supports "within subnet" anycast, where the
source and the anycast address fall within the same prefix. Traditional anycast
relies on packets entering the routing/forwarding domain, so it isn't possible
to use anycast between hosts on the same subnet. IPv4 ARP use of the most
recent reply as well as duplicate address detection prevents this from working,
where as IPv6 has been changed to support it by using the first rather than
last NA received when the address is an anycast, and allowing duplicate
addresses to exist within a subnet when they've been flagged as anycast
addresses.
The use cases for IPv6 anycast are the same as IPv4's, with the IPv4
restriction that anycast destinations must always be outside of the subnet of
the source address removed.
Regarding things like subnet-router anycast, Appletalk implemented this concept
(Pg 4-7, Inside Appletalk, 2nd Ed.), and it was used by the Name Binding
Protocol. Whether it was invented independently for IPv6 or inspired by
Appletalk is something people like Bob would know.
> Bob
>
>
>
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