Virtual Private LAN Services
7210 SAS-X, R6 OS Services Guide Page 261
VPLS Access Redundancy
A second application of hierarchical VPLS is using that are MPLS-enabled which must have
spoke SDPs to the closest PE node. To protect against failure of the PE node, an MTU can be dual-
homed.
Listed below are several mechanisms that can be used to resolve a loop in an access circuit,
however from operation perspective they can be subdivided into two groups:
• STP-based access, with or without mVPLS.
STP-Based Redundant Access to VPLS
Figure 33: Dual Homed MTU-s in Two-Tier Hierarchy H-VPLS
In configuration shown in Figure 33, STP is activated on the MTU and two PEs in order to resolve
a potential loop.
In order to remove such a loop from the topology, Spanning Tree Protocol (STP) can be run over
the SDPs (links) which form the loop such that one of the SDPs is blocked. Running STP in every
VPLS in this topology is not efficient as the node includes functionality which can associate a
number of VPLSes to a single STP instance running over the redundant SDPs. Node redundancy
is thus achieved by running STP in one VPLS. Thus, this applies the conclusions of this STP to the
other VPLS services.
The VPLS instance running STP is referred to as the “management VPLS” or mVPLS. In the case
of a failure of the active node, STP on the management VPLS in the standby node will change the
link states from disabled to active. The standby node will then broadcast a MAC flush LDP
control message in each of the protected VPLS instances, so that the address of the newly active
node can be re-learned by all PEs in the VPLS. It is possible to configure two management VPLS
OSSG206
s
S
S
s S
PE-1
CE-1
Customer
Site 1
Primary Spoke
Pseudowire
Backup Spoke
Pseudowire
Customer
Site 2
CE-1
(MTUs)
PE-3
PE-2
H-VPLS Full
Mesh
Core
PE-4
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