VPN EVPN BGP Ext Communites

Introduction

EVPN introduced a number of extended communities. This document describes them and their usage.

Overview

  • Below is the list of EVPN BGP Extended Communities:
    • ESI Label Extended Community -
    • ES-Import Route Target -
    • MAC Mobility Extended Community -
    • Default Gateway Extended Community -

ESI Label Extended Community

  • Advertised with Ethernet Auto Discovery Routes.
  • See the format below.
    • Type 0x06 is the EVPN type.
    • Flags (low order bit) is designated load balancing type:
      • 0 - Single Active
      • 1 - All Active

ES-Import Route Target

  • This extended community is carried in the Ethernet Segment route.
  • It includes the ESI of associated with the Ethernet Segment route. All PEs that are connected to the same ESI should import routes tagged with ES-Import RT that matches their MAC VRF and filter all others.
  • This community is used in the process of discovery other PE connected to the same CE with the same ESI.
  • Transitive extended community.
  • Route Target filtering has to support this RT values for filtering.

MAC Mobility Extended Community

  • This extended community is used when a MAC moves from one PE to another PE segment.
  • It is added to MAC/IP Advertisement Route.
    • The community has a seq number to account for order of operations. It start with 0 for the first one advertised.
  • The new PE learns of a MAC address which has been previously advertised by another PE. The old one might still have it cached. With two MAC routes advertised, the old PE will be blackholing frames.
  • MAC Mobility Extended Community was added to minimize blackholing. It works the following way:
    • New PE locally learns of a MAC address that was previously learned remotely from another PE with a different ESI.
    • It generates the MAC Advertisement Route, but it also attaches the MAC Mobility Ext Comm attribute. If this is the first MAC Mobility Ext Community attribute attached it will set the seq to 0 if not first, then increment it.
    • When the original PEs receive this advertisement, it compares the ESI and the sequence of number. If ESI is different and the sequence number is higher than the previously advertised MAC route, it will withdraw the MAC route.
    • Other PEs will remove any other older MAC routes for this MAC address.

Default Gateway Extended Community

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