[j-nsp] EVPN all-active toward large layer 2?

[adamv0025 at netconsultings.com]

> Rob Foehl
> Sent: Thursday, April 18, 2019 6:43 AM
> 
> First and foremost, is a topology like this even a valid use case?
> 
> EVPN PE <-> switch <-> switch <-> EVPN PE
> 
> ...where both switches are STP root bridges and have a pile of VLANs and
> other switches behind them.  All of the documentation seems to hint at
LACP
> toward a single CE device being the expected config here -- is that
accurate?
> If so, are there any options to make the above work?
> 
When I first heard of active-active for EVPN I thought yeah mac-level
load-sharing! Perfect that's just like in L3 world.
But then I realized that the only available solution to do that was to
reduce your topology to:
EVPN PE <-> switch
With some clever tricks like using MC-LAG. 
Without these the only level at which one can do load-sharing is at the VLAN
level.
That is active-standby with one half of VLANs active on PE1 and other half
active on PE2.

I came to conclusion that the ultimate problem why true MAC level
active-active is not possible in EVPN is not limitation of EVPN itself, but
rather is a limitation of the L2 domain where it boils down to a fact that
you can't have a single MAC address associated with two ports at the same
time (like it's possible with L3 routes), which I don't really know why that
is the case. 

adam