BGP EVPN. A view from the field#

Alex Mitev - Cisco System

• Why: EVPN is consolidating L2/L3 service delivery and DCI under one BGP control plane, and this is a field-density walkthrough of design options and — most valuably — in-service migration paths from legacy redundancy schemes. Relevant to both DC fabric and telco access work.
• What: The core framing: EVPN (RFC 7432/7623/8214/9135) replaces MC-LAG/ICCP, ICCP-SM, nV Edge, and VPLS flood-and-learn by moving coordination into BGP — deleting peer-links and sync protocols, eliminating split-brain, enabling N-way multi-vendor multihoming; risk changes shape ("more failure events, smaller blast radius — each one survivable"). Multihoming modes mapped: all-active (per-flow), single-active (per-VLAN), port-active (per-port), plus single-flow-active for L2 ring protocols (G.8032/STP-AG). Migration recipes with actual IOS-XR config: MC-LAG → port-active EVPN (no CE change, NDF sets LACP out-of-service, then ICCP removed); VPLS → EVPN (add EVI, PEs auto-discover, pseudowires shut down; both VFIs and EVIs default to split-horizon group 1 so no PE forwards between them during transition); VPWS seamless integration where EVPN VPWS is preferred over the legacy PW when both exist for the same AC; nV Edge is the one migration requiring downtime (de-clustering). Also covers hierarchical EVPN (EVPN-HE) with P-bit/B-bit service carving, flexible cross-connects to bundle thousands of services into fewer tunnels (cutting BGP state and OAM), and real Australian use cases: RSPs delivering BNG services over EVPN with SRG-driven service carving, and wholesale fan-in (thousands of L2 sub-ifs onto BNG pairs) solved via VLAN-aware FXC and L2 NNI handoff.
• How: Config-level sequencing and DF-election/service-carving modes (preference-based, access-driven, srg-driven) with show-command output from a lab.
• Where applicable: SP access/aggregation and enterprise DCI. This is a Cisco SE session with IOS-XR-specific configs — vendor-flavored, but the design concepts and migration orderings are multi-vendor standards work and directly reusable.