EVPN Overview

Introduction

EVPN is a L2VPN technology that builds upon some of the limitations of VPLS.

Overview

  • Currently EVPN is adapted by Alcatel, Juniper and Cisco. Cisco supports PBB-EVPN (the more advanced version of EVPN).
  • EVPN is an E-LAN type of Ethernet connectivity.
  • It is similar to the L3VPN MPLS but for Ethernet.
  • It relies on the MP-BGP protocol for control plane.
  • Based on the IETF draft draft-ietf-l2vpn-evpn
  • PEs advertise MAC addresses learned from CE directly connected to other PEs along with the MPLS labels.
  • MAC learning is performed on the control plane between the PEs and not in data plane as in VPLS. MAC learning still uses data plane MAC learning between the CE and PEs.
  • Similarities to L3VPN MPLS:
    • EVPN Instance had RDs and RTs.
    • CEs are connected to a MAC-VRF

Topologies

  • There are four main topologies that can be used with EVPN which include:
evpn-topology.PNG
  • Single-Homed Device (SHD)
    • CE connected to only one PE.
  • Single-Homed Network (SHN)
    • CE connected to a single Network.
  • Multi-Homed Device (MHD)
    • CE connected to multiple PEs.
  • Multi-Homed Network (MHN)
    • Same network connected to multiple PEs.

Ethernet Segment

  • If a CE is multi-homed the links between CE and PEs are called the Ethernet Segment.
  • The Ethernet Segment is distinguished with an Ethernet Segment ID (ESI).
  • There are two reserved ESI value:
    • 0 - for single homed CE.
    • 0xFF - reserved as the MAX-ESI.
  • The Ethernet Segment should use a non reserved value and should be unique for all EVPN instances.
  • The ESI is made up of the ESI type and the ESI Value:
    • There are six types:
      • Type 0 =0x00 - ESI manually configured by the operator.
      • Type 1 =0x01 - ESI automatically configured when LACP is used between the PEs. ESI is derived from CE's system MAC and port key.
      • Type 2 =0x02 - ESI automatically configured using the L2 bridge protocol. ESI derived from Root Bridge MAC address and CE root port priority.
      • Type 3 =0x03 - ESI automatically configured or manually by the operator based on a PE MAC address. ESI derived from PE MAC address and local discriminator value.
      • Type 4 =0x04 - ESI automatically configured or manually by the operator based on a router-id. ESI derived from router-id and local discriminator value.
      • Type 5 =0x05 - ESI automatically configured or manually by the operator based on an ASN. ESI derived from ASN and local discriminator value.

BGP

  • EVPN introduces a new MP-BGP NLRI. For more information see VPN-EVPN-BGP.
  • EVPN introduces new BGP extended communities some of these include:
    • ESI Label Extended Community
    • ES-Import Route Target
    • MAC Mobility Extended Community
    • Default Gateway Extended Community
  • For more information their functionality see VPN-EVPN-BGP-Ext-Communites

Additional Resources

EVPN Introduction Next Generation L2VPN - packet pushers blog.
Draft IETF L2VPN EVPN-11 - BGP MPLS Based Ethernet VPN

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