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[v6ops] Use of MAC addresses in IPv6 link local addresses

Toerless Eckert <tte@cs.fau.de> Thu, 06 July 2017 23:03 UTC

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Date: Fri, 07 Jul 2017 01:03:47 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: v6ops@ietf.org
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Archived-At: <https://mailarchive.ietf.org/arch/msg/v6ops/Ez2L2J7UMlTEWkHcAWLe2OIRFc4>
Subject: [v6ops] Use of MAC addresses in IPv6 link local addresses
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For a protocol design, we are wondering what the current state of the
art is wrt to IPv6 link local addresses potentially being the same
on multiple interfaces of a network device like a router.

I was told by Brian that RFC7217 is recommended, but recommendations are
one thing and reality can be another thing. If there are widely deployed
network devices that do have the same link local address across multiple
interfaces then it could take quite a while for this to get changed,
so it might be prudent for a protocol design NOT to expect that eg: RFC7217
is supported everywhere.

The one type of datapoint i seem to vaguely remember is that routers
with large number of "cheap" L3 interfaces often derive their MAC
utilization designs from L2 switches where you do not automatically
assign a separate MAC address to every port because thats a cost factor,
and instead there is just a limited number of MAC addresses assigned to
the box (i think i remember '8' from some cisco products) and
once those are exhausted, additional L3 interfaces repeat the MAC
addresses. And of course if the link-local addresses are derived from
interfaces MAC addresses then we have the problem in question.

Standard disclaimer:
Just because i am paranoid does not mean they are not after me.

So, would love to hear that duplicate link-local IPv6 addresses are
not to be found anywhere in deployed  IPv6 networks and that i am
just paranoid ;-) Or else we know that we should take this into
consideration.

Thanks
    Toerless

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