Juniper JUNOSE 11.2.X BGP AND MPLS, Руководство по настройке

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PWid FEC Element TLV
LDP signaling information for VPLS is carried in a label mapping message. The label
mapping message contains the Generic Label type-length-value (TLV), and the
pseudowire identifier (PWid) forwarding equivalence class (FEC) element. A FEC is a
group of IP packets forwarded over the same path with the same path attributes applied.
The PWid FEC element (FEC Type 128 or 0x80) contains the VPLS identifier information
configured for your VPLS instance with the
mpls ldp vpls-id command. Taken together,
the pseudowire type field and the PWid field in the TLV represent a unique VPLS instance.
The pseudowire type field is Ethernet to identify the pseudowires that carry Ethernet
traffic for multipoint connectivity between the local and remote VEs. The PWid field is
a nonzero 32-bit integer that contains the VPLS identifier, which is a globally unique
identifier for a VPLS domain. All VEs that participate in the same VPLS domain must use
the same VPLS identifier.
Martini encapsulation for Ethernet layer 2 services over MPLS also uses the PWid FEC
Element TLV. As a result, the PWid for Martini configurations must not be the same as
the VPLS identifier configured for a VPLS instance. To prevent this conflict from occurring,
the JunosE Software displays an error and rejects the configuration if you attempt to
configure the same value for the Martini PWid and the VPLS identifier.
Related Topics Configuring LDP Signaling for VPLS on page 604
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Configuring MPLS on page 275.
BGP Multihoming for VPLS 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 VPLS 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.
When a CE device connects to multiple PE routers, each of these routers advertises
reachability for the multihomed site—routes that have the same site ID in the layer2 NLRI.
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 VPLS 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.
581 Copyright © 2010, Juniper Networks, Inc.
Chapter 11: VPLS Overview