Migrating a traditional Layer 2/3 campus to EVPN-VXLAN doesn't require a forklift upgrade. Here's our field-tested approach to phased overlay introduction.
EVPN-VXLAN is no longer data-centre-only technology. Arista, Cisco, and Juniper now support campus EVPN fabrics that simplify segmentation, eliminate spanning tree, and enable workload mobility across buildings.
The Brownfield Challenge
Most campus networks can't be rebuilt from scratch. You need to introduce the overlay incrementally — building by building, closet by closet — while maintaining connectivity to the legacy underlay.
Our 4-Phase Migration
- Phase 1 — Spine readiness: Upgrade core switches to support VXLAN VTEP and BGP EVPN. Configure iBGP with route reflectors.
- Phase 2 — Pilot overlay: Deploy EVPN-VXLAN on one building's access/distribution. Gateway between overlay and legacy via external connectivity (border leaf).
- Phase 3 — Expand: Migrate buildings one at a time. Each new VTEP extends the fabric; legacy VLANs are stitched via anycast gateway.
- Phase 4 — Decommission: Remove legacy STP domains, consolidate VRFs, and enable distributed anycast gateway everywhere.
The key insight: the border leaf is your friend. It translates between the VXLAN overlay and legacy VLANs, allowing coexistence for as long as you need.