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The procedures for configuring BGP signaling for BGP/MPLS VPNs and for VPWS L2VPNs

are similar except that for VPWS L2VPNs you must configure both of the following

address families:

•

L2VPN—The L2VPN address family enables you to configure the PE router for VPWS

(or VPLS) L2VPNs to exchange layer 2 network layer reachability information (NLRI)

for all VPWS (or VPLS) instances. Optionally, you can use the signaling keyword with

the address-family command for the L2VPN address family to specify BGP signaling

of VPWS reachability information. Currently, you can omit the signaling

keyword with no adverse effects.

•

VPWS—The VPWS address family enables you to configure the PE router to exchange

layer 2 NLRI for a specified VPWS instance.

BGP can exchange information in an L2VPN topology within these address families.

Related Topics Configuring BGP Routing on page 3•

• Configuring BGP-MPLS Applications on page 383

BGP Multihoming for VPWS Overview

BGP multihoming enables you to connect a customer site to two or more PE routers to

provide redundant connectivity while preventing the formation of layer 2 loops in the

service provider’s network. The redundant connectivity maintains the VPWS service and

traffic forwarding to and from the multihomed site in the event of a PE router-to-CE

device link failure, the failure of a PE router, or an MPLS reachability failure between the

local PE router and a remote PE router. A redundant PE router can begin providing service

to the customer site as soon as the failure is detected. BGP multihoming is very similar

for both VPLS and VPWS, with only minor differences in behavior between the two L2VPN

types. Multihoming is not applicable for VPWS local cross-connects because the local

and remote CE devices are connected to the same PE.

When a CE device connects to multiple PE routers, each of these routers advertises

reachability for the multihomed site. The other PE routers in the network use a BGP path

selection process to select only one of the advertising routers to which they send traffic

destined for the CE device. This path selection process eliminates layer 2 loops in the

VPWS network.

BEST PRACTICE: To prevent the creation of layer 2 loops due to a misconfiguration or

temporary loops during a topology change and subsequent convergence, we recommend

that you employ the Spanning Tree Protocol (STP) on your CE devices.

You specify on each PE router connected to the CE device in the VPWS that the site is

multihomed and you configure a priority. The priority serves as a site preference and is

propagated by BGP in the local-preference attribute.

You configure the same site ID (sometimes referred to as a VE ID) on these connected

PE routers. Each of these routers then advertises reachability for the multihomed site;

JunosE 11.2.x BGP and MPLS Configuration Guide

Juniper JUNOSE 11.2.X BGP AND MPLS User Manual

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