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;
Copyright © 2010, Juniper Networks, Inc.
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