MPLS in the SDN Era

Chapter 8. Ethernet VPN

Ethernet VPN (EVPN) is not Virtual Private LAN Service (VPLS). It is a more recent technology that aims to overcome some of the challenges that have arisen during more than a decade of VPLS live deployments.

EVPN with MPLS Transport

EVPN, formerly called MAC VPN, is described in RFC 7432 - BGP MPLS-Based Ethernet VPN.

EVPN Versus VPLS

If there was already a multipoint L2VPN solution (VPLS), why has another one been defined and implemented? Let’s compare both technologies.

EVPN versus VPLS—signaling protocols

VPLS has two possible signaling protocols, LDP and BGP, of which only BGP supports autodiscovery. EVPN takes good note of that by deprecating Targeted LDP and adopting BGP as the one and only service signaling protocol.

EVPN versus VPLS—MAC address learning

VPLS has only data-plane MAC learning, which can easily lead to stale forwarding state.

Indeed, if a local Attachment Circuit (AC) goes down, it is important to flush the associated MAC entries from the bridge table. You must do this on the local PE, and also on the remote PEs. The PW Status TLV is not a valid option, due to the lack of an AC:PW deterministic mapping in VPLS. True, VPLS has the concept of a MAC Flush flag (BGP VPLS) or TLV (LDP VPLS), but it is more like a patch than a robust solution.

Although EVPN also performs data-plane MAC learning on its local ACs, it relies on control-plane MAC learning between PEs. In fact, it uses BGP to exchange MAC address routes. This greatly reduces ...