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

Fri Feb 10 00:41:05 UTC 2023

Hi Simon,

This looks like an interesting project. What are you ultimately trying to
achieve?

Stretching an Ethernet segment between sites shouldn't be the first choice,
but I imagine you're having to deal with some legacy use case and your
hands are tied. I'm a little curious on what that might look like.

Best,
Josh

On Thu, Feb 9, 2023, 02:50 Simon Lockhart <simon at slimey.org> wrote:

> 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
>
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