Bgp Signaling For L2Vpns Overview; Table 132: Components Of Vpws Nlri - Juniper JUNOSE 11.2.X BGP AND MPLS Configuration Manual

BGP Signaling for L2VPNs Overview

Copyright © 2010, Juniper Networks, Inc.
Local and remote site information for the interfaces identifies the cross-connect. Local
cross-connects are supported when the interfaces that are connected belong to two
different sites configured in the same VPWS instance and on the same PE router.
BGP advertises reachability for the VPNs. The BGP configuration is similar to that used
for other VPN services, such as layer 3 VPNs and VPLS. MPLS is configured to set up base
LSPs to the remote PE routers similarly to the other VPN services.
When you configure VPWS at a given PE router for a given L2VPN customer, BGP signals
reachability for all sites that belong to that L2VPN. This signaling is identical to the
signaling used for BGP/MPLS VPNs and VPLS. The network layer reachability information
(NLRI) for both services are encoded in a similar manner.
A new NLRI format carries the individual VPWS information listed in Table 132 on page 641.
One or more of these NLRIs is carried in the MP_REACH_NLRI and MP_UNREACH_NLRI
BGP attributes.

Table 132: Components of VPWS NLRI

NLRI value Size in octets
Length 2
Route Distinguisher 8
CE-ID 2
Label-block Offset 2
Label Base 3
Variable TLVs 0–n
The local PE router selects a contiguous label block to cover all the remote sites for a
given VPWS instance. The local PE router then advertises that label block as part of the
reachability information for a given CE device in a particular VPWS instance; (the NLRI
contains the CE-ID (site ID) for the CE device. This label block represents the set of
demultiplexers that are used to cross-connect incoming MPLS traffic to a specific local
interface in the VPWS instance..
The local PE router also processes advertisements from all remote PE routers and for
each local interface in an VPWS instance. The local PE router selects a demultiplexer
label from a label block received from the remote PE router associated with each remote
site in the VPWS instance. Traffic coming into the local interface from the CE device is
cross-connected to an MPLS next hop that corresponds to the demultiplexer. Traffic is
then encapsulated in MPLS and sent across the MPLS core to the remote PE router in
the L2VPN.
Chapter 14: VPWS Overview
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