EVPN Route Target Considerations in EBGP Environment

The proponents of the “let’s run EVPN over EBGP underlay” idea often ignore an interesting challenge: EVPN advocates the use of automatically-generated Route Targets, which might not work when every leaf switch uses a different AS number.

I explored this particular can of worms in the EVPN Route Target Considerations section of the Using BGP in a Data Center Leaf-and-Spine Fabric saga.


  1. Good hint from @ioshints
  2. At least Juniper supports an option to have eBGP as an underlay routing protocol and iBGP as an overlay, allowing to have unique ASN in underlay and common ASN in overlay, thus making it possible to use automatic RTs.
    1. Most everyone supports that - but it makes for a really messy BGP setup. It's easier to run IBGP-over-IGP in that case unless you have more than hundred or so switches in your fabric.
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