Re: <draft-ietf-6man-rfc4291bis-09.txt>

On 11 July 2017 at 06:52, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
> Fred,
>
> On 11/07/2017 03:52, Templin, Fred L wrote:
>> Hi, something that I think is a bit under-specified is whether the address "fe80::"
>> should be considered as an Anycast address. In particular, the leftmost 10 bits
>> are "link-local" and the rightmost 118 bits are all-zero.
>>
>> Should fe80:: be considered as the subnet router Anycast address for "link-local"?
>> If so, I think that it could be mentioned somewhere in Section 2.5 that even the
>> link-local subnet has an Anycast address.
>
> I don't think so. The text in 4291 about the Subnet-Router anycast address says:
> 'The "subnet prefix" in an anycast address is the prefix that identifies a specific link.'
> fe80::/10 does not identify a specific link, since it applies to every link.
> Therefore, fe80:: is logically not a subnet-router anycast address.
>

I would disagree. fe80::/64 identifies a specific link - it identifies
the link the host is attached to - "this" link.

fe80::/64 could also be described as an anycast prefix, because it is
assigned to multiple links. Other prefixes can be anycast prefixes
too.

The forwarding system sends to the closest instance of an anycast
prefix, which in the case of fe80::/64 is always on-link, for other
anycast prefixes it may not and usually won't be. The only thinh
special about fe80::/64 in this context is that is automatically
configured on all links, so it is never an off-link anycast fe80::/64
prefix.

I think this text would have to specifically exclude fe80::/64 if
fe80::/128 is not a router-subnet anycast address.

"Packets sent to the Subnet-Router anycast address will be delivered
   to one router on the subnet.  All routers are required to support the
   Subnet-Router anycast addresses for the subnets to which they have
   interfaces."

Regards,
Mark.

>     Brian
>
>>
>> Thanks - Fred
>>
>>> -----Original Message-----
>>> From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Bob Hinden
>>> Sent: Monday, July 03, 2017 10:36 AM
>>> To: IPv6 List <ipv6@ietf.org>
>>> Cc: Bob Hinden <bob.hinden@gmail.com>
>>> Subject: <draft-ietf-6man-rfc4291bis-09.txt>
>>>
>>> Hi,
>>>
>>> I published a new 6man w.g. version (-09) of the RFC4291bis draft.  See links below.
>>>
>>> The summary of the changes are:
>>>
>>>        o   Added text to the last paragraph in Section 2.1 to clarify
>>>            the differences on how subnets are hangled in IPv4 and IPv6,
>>>            includes a reference to RFC5942 "The IPv6 Subnet Model: The
>>>            Relationship between Links and Subnet Prefixes".
>>>
>>>        o   Removed short paragraph about manual configuration in
>>>            Section 2.4.1 that was added in the -08 version.
>>>
>>>        o   Revised "Changes since RFC4291" Section to have a summary of
>>>            changes since RFC4291 and a separate subsection with a change
>>>            history of each Internet Draft.  This subsection will be
>>>            removed when the RFC is published.
>>>
>>>        o   Editorial changes.
>>>
>>> A diff from the previous version is available at:
>>>
>>>  https://www.ietf.org/rfcdiff?url2=draft-ietf-6man-rfc4291bis-09
>>>
>>> This is part of the project to move the core IPv6 specifications to Internet Standard.
>>>
>>> Thanks,
>>> Bob
>>>
>>>> A new version of I-D, draft-ietf-6man-rfc4291bis-09.txt
>>>> has been successfully submitted by Robert M. Hinden and posted to the
>>>> IETF repository.
>>>>
>>>> Name:               draft-ietf-6man-rfc4291bis
>>>> Revision:   09
>>>> Title:              IP Version 6 Addressing Architecture
>>>> Document date:      2017-07-03
>>>> Group:              6man
>>>> Pages:              35
>>>> URL:            https://www.ietf.org/internet-drafts/draft-ietf-6man-rfc4291bis-09.txt
>>>> Status:         https://datatracker.ietf.org/doc/draft-ietf-6man-rfc4291bis/
>>>> Htmlized:       https://tools.ietf.org/html/draft-ietf-6man-rfc4291bis-09
>>>> Htmlized:       https://datatracker.ietf.org/doc/html/draft-ietf-6man-rfc4291bis-09
>>>> Diff:           https://www.ietf.org/rfcdiff?url2=draft-ietf-6man-rfc4291bis-09
>>>>
>>>> Abstract:
>>>>   This specification defines the addressing architecture of the IP
>>>>   Version 6 (IPv6) protocol.  The document includes the IPv6 addressing
>>>>   model, text representations of IPv6 addresses, definition of IPv6
>>>>   unicast addresses, anycast addresses, and multicast addresses, and an
>>>>   IPv6 node's required addresses.
>>>>
>>>>   This document obsoletes RFC 4291, "IP Version 6 Addressing
>>>>   Architecture".
>>>>
>>
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