Can I do this in EVPN? (Multihome to more different CEs)

Thu Feb 9 07:47:12 UTC 2023

All,

I have a bit of a networking design challenge, and I thing EVPN is the right
answer, but despite spending the last week reading loads of resources about
it, I can't quite get my head around one aspect.

I'm trying to genericise the design a bit here, but what I've got is...

I have multiple layer two broadcast domains that I need to link together 
over a layer 3 network. The broadcast domains consist of multiple switches
carrying multiple vlans spanning multiple locations (think of it like a 
customer campus network).

I need to interconnect with each broadcast domain in two different locations.
(so two PEs to two CEs), and link it back to a datacentre in another city.

In the simple case, using EVPN, I see that I can run active-standby 
multihoming, configuring one ESI for the customer campus network. If one of my
PEs fails, or one of the customer CEs fails, then EVPN will fail over to the
other link.

However, the failure scenario I need to deal with is if a layer two link fails
between two locations within the customer campus, the two halves of the now
split broadcast domain still need to be able to communicate with the 
datacentre (but do not need to be able to communicate with each other).

Every example I can see for EVPN shows multihoming to a single CE, and I 
can't find anywhere an example which deals with a "split" ES.

Is there a solution to this problem?

Many thanks in advance,

Simon