BGP EVPN Control Plane Route advertisement — Part-1 (mac-route)

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 Topology

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Mac Advertisement

To start with how the MAC address of the Host H1 is advertised and eventually settles in the MAC address table of remote VTEPS, let’s inspect the tables involved in advertising VTEP L1.

The Tables involved are :

  1. Mac address Table
  2. MAC VRF table ( L2 EVPN RIB )
  3. BGP Local RIBs

The Data is pushed from the previous table to the next table in sequence as listed above :

MAC Table --------> MAC VRF Table --------> BGP Local RIBs

MAC VRF table is created per VNI. So, we have two MAC VRF tables — one for VNI5010 and one for VNI5020. Since VLAN 10 is associated with VNI 5010, all MAC addresses present in VLAN 10 are pushed into MAC VRF table for VNI5010. This table contains MAC-only routes as exported from mac-address table. Each MAC VRF table is also configured with RD and RT. BGP process is listening on these MAC VRF tables to export MAC routes as EVPN TYPE 2 Routes along with RDs and RTs configured on these tables.

Route Export Procedure (Leaf-1)

Let’s start step by step :

  1. Host H1, has two ways to notify VTEP 10.0.0.1 about its presence :

a. Generate GARP when booting up

b. Initiate communication ( ARP msg will be generated )

2. Either of the two methods will send VTEP the ARP message from Host H1. VTEP analyzes only the Src MAC Address embedded in the ARP message. In this case, Src mac address is MAC(H1) = 0c08.4e22.0001

3. VTEP processes the ARP message in a way we described in the previous article, we will confine our discussion here regarding how this MAC address is learned and advertised by VTEP

4. As soon as VTEP receives ARP message from Host H1, it inserts an entry into its mac address table

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5.This new entry is pushed from MAC Address table to MAC VRF table corresponding to vlan 10

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6.Finally, BGP reads the routes from MAC VRF table and exports the MAC Routes along with their attributes ( VNI, RD, RT ). BGP maintains its EVPN Address Family RIBS keyed by VNIID.

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Route Import Procedure (Leaf-4)

1.Checking the BGP EVPN Address Family RIBS on VTEP 10.0.0.4.

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2.The next Step is to insert the BGP Route in L2 EVPN RIBs / MAC VRF table based on the Route’s RT value

This Route’s Route target value is 10, so matching MAC VRF table on local VTEP with same RT value is MAC VRF table for VNI 5010 ( as per the config ). Hence route will be imported in MAC VRF table for VNI 5010.

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3.Finally, the route is installed in MAC Address table of VTEP 10.0.0.4

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