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

[Jen Linkova <[e-mail]>]

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