Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual page 686

JUNOSe 11.1.x BGP and MPLS Configuration Guide
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:
BGP can exchange information in an L2VPN topology within these address families.
Related Topics
BGP Multihoming for VPWS
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.
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BGP Multihoming for VPWS
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.
Configuring BGP Routing on page 3
Configuring BGP-MPLS Applications on page 379