Re: I-D Action: draft-linkova-6man-default-addr-selection-update-00.txt

[Erik Kline <[e-mail]>]

On 7 April 2017 at 22:04, Jen Linkova <[e-mail]> wrote:

> On Wed, Apr 5, 2017 at 4:35 AM, Mark Smith <[e-mail]> wrote:
> > On 5 April 2017 at 08:18, Brian E Carpenter <[e-mail]>
> wrote:
> >> As far as I can see this proposal makes sense and should work. But:
> >>
> >>>    1.  The link-local address of the router in the new layer 2 domain
> >>>        might be the same as the link-local address of the "old" router
> >>>        (it's quite common to have link-local address on routers to be
> >>>        explicitly configured, especially in VRRP-enabled environments)
> >>
> >> Wow. Shouldn't there also be an operational recommendation to configure
> >> non-clashing or at least highly-unlikely-to-clash addresses for
> >> such routers?
> >>
> >
> > I think RFC8064, "Recommendation on Stable IPv6 Interface Identifiers"
> > is indirectly making that recommendation.
> >
> > One of the use cases of RFC7217 is for router interface's Link-Local
> > addresses, and to not use use the interface's MAC address as the
> > Net_Iface value (e.g., module/slot number, ifindex instead), so that
> > the router's Link-Local IID is both unique and doesn't change if the
> > physical interface module is replaced, which usually means an
> > interface MAC address change too.
>
> I probably need to make the text a bit more clear but the use case
> I've observed has nothing to do with SLAAC, so neither
> RFC 7217 nor RFC8064 are applicable here. People do configure VRRP LLAs
> manually
> (see http://www.juniper.net/documentation/en_US/junos/topics/reference/
> configuration-statement/virtual-link-local-address-edit-interfaces.html
> and http://www.cisco.com/c/en/us/td/docs/routers/crs/software/
> crs_r4-2/addr_serv/configuration/guide/b_ipaddr_cg42crs/b_ipaddr_cg42crs_
> chapter_01010.html#task_96270599CAEE43DDB370F262D8C0722A
> for two random examples)
>
> and it's understandable that they do not want to generate an unique
> LLA for each interface (LLAs are supposed to be unique within a link,
> right? so it's perfectly fine to have fe80::1 configured on each
> interface).
> It's operational reality, it does make sense (or we shall stop
> pretending that  LLAs have link scope...;( ) so I believe it would be
> nice to tweak the source address selection a bit to deal better with
> the real life..;)
>
>
> --
> SY, Jen Linkova aka Furry
>
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It is a sad, but seemingly true, state of affairs that all of this blows up
the core DNAv6 working assumption:

    https://tools.ietf.org/html/rfc6059#section-1.5

   o  The combination of the link-layer address and the link-local IPv6
      address of a router is unique across links.