- Don’t make things too complex;
- Don’t add more risk than you take away;
- You’ve got to fail over in the right direction;
- You must be able to return to fully-redundant mode.
I’m guessing that people promoting stretched VLANs, vSphere and/or NSX clusters running across multiple sites, weird combination of EVPN and OTV, and a dozen similar shenanigans never considered any one of these points.