Configuring MPLS EVPN E-LAN Option B

In a scenario in which the backbone network spans two ASs, ASBRs need to advertise BGP-EVPN routes through MP-EBGP.

Usage Scenario

If an ASBR can manage BGP-EVPN routes but there are not enough interfaces for all inter-AS EVPNs, MPLS EVPN E-LAN Option B can be used. MPLS EVPN E-LAN Option B requires ASBRs to help to maintain and advertise EVPN routes, and you do not need to create EVPN instances on the ASBRs. In the basic networking of inter-AS VPN Option B, an ASBR cannot play other roles, such as the PE or RR, and an RR is not required in each AS.

On the network shown in Figure 1, the interfaces connected between ASBRs do not need to be bound to the EVPN. A single-hop MP-EBGP peer relationship is set up between the ASBRs to transmit all inter-AS EVPN routing information.

Figure 1 MPLS EVPN E-LAN Option B networking

Pre-configuration Tasks

Before configuring MPLS EVPN E-LAN Option B, complete the following tasks:

Configure an IGP for the MPLS backbone network of each AS to ensure IP connectivity of the backbone network in each AS.
Configure MPLS and MPLS LDP both globally and per interface on each node of the MPLS backbone network in each AS and establish an LDP LSP or TE tunnel between MP-IBGP peers.
Configure Configuring an EVPN Instance on the PE connected to the CE.
Configure Configuring an EVPN Source Address on the PE connected to the CE.
Configure Binding an Interface to an EVPN Instance on the PE connected to the CE.
Configure Configuring an ESI on the PE connected to the CE.

Configuring MP-IBGP Between a PE and an ASBR in the Same AS: By introducing extended community attributes into BGP, MP-IBGP can advertise BGP-EVPN routes between the PE and ASBR.

Configuring MP-EBGP Between ASBRs in Different ASs: Configuring MP-EBGP Between ASBRs in Different ASs

Configuring ASBRs Not to Filter EVPN Routes Based on VPN Targets: In inter-AS EVPN OptionB mode, ASBRs do not have EVPN instances. If you want ASBRs to keep received EVPN routes, configure ASBRs not to filter EVPN routes based on VPN targets.

(Optional) Configuring One-Label-per-Next-Hop Label Distribution on an ASBR: To save label resources on an ASBR, configure one-label-per-next-hop label allocation on the ASBR. One-label-per-next-hop label allocation on ASBRs and one-label-per-instance label distribution on PEs must be used together.

(Optional) Configuring the Protection Switching Function: A protection switching function, such as link or node protection, can be configured to provide high availability for an inter-AS EVPN-OptionB network.

(Optional) Configuring BGP-EVPN Route Reflection on an ASBR: When multiple PEs exist in the ASs, you can configure an ASBR as an RR to lower configuration complexity.

Verifying the Configuration MPLS EVPN E-LAN Option B: After configuring MPLS EVPN E-LAN Option B, check the status of all BGP peer relationships and EVPN routing information on PEs or ASBRs.