Forwarding issues related to MACs starting with a 4 or a 6 (Was: [c-nsp] Wierd MPLS/VPLS issue)

Nick Hilliard nick at
Fri Dec 2 21:16:58 UTC 2016

Job Snijders wrote:
> I consider this a cascading failure. Clearly IEEE's change had a ripple
> effect, and suprised a number of implementers, and ended up hurting us.

this would be credible if this were a previously unknown problem, but it
isn't.  It's been known for years that you need to be careful when
handling mpls encapsulated packets which encapsulate L2 frames and where
the source mac address starts with 4 or 6.  This is not a new problem
and because it's not new, there is no good reason for vendors to make
the same mistakes again and again.  TBH, it beggars belief that new L2
hardware is being thrown out the door which is unable to forward frames
of this form due to hardware limitations, and that it's apparently


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