Juniper ACX1000 Configuration Manual page 1296

ACX Series Universal Access Router Configuration Guide
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Although you configure the same site ID for each of the PE routers multihomed to the
same CE device, you can configure unique values for other parameters, such as the route
distinguisher. These values help to determine which multihomed PE router is selected
as the designated VE device to be used to reach the customer site.
BEST PRACTICE:
distinguishers for each multihomed PE router. Configuring unique route
distinguishers helps with faster convergence when the connection to a primary
multihomed PE router goes down. If you configure unique route distinguishers,
the other PE routers in the VPLS network must maintain additional state for
the multihomed PE routers.
Remote PE routers in the VPLS network need to determine which of the multihomed PE
routers should forward traffic to reach the CE device. To make this determination, remote
PE routers use the VPLS path-selection process to select one of the multihomed PE
routers based on its NLRI advertisement. Because remote PE routers pick only one of the
NLRI advertisements, it establishes a pseudowire to only one of the multihomed PE
routers, the PE router that originated the winning advertisement. This prevents multiple
paths from being created between sites in the network, preventing the formation of
Layer 2 loops. If the selected PE router fails, all PE routers in the network automatically
switch to the backup PE router and establish new pseudowires to it.
BEST PRACTICE:
devices and the multihomed PE routers, we recommend that you employ the
Spanning Tree Protocol (STP) on your CE devices. Layer 2 loops can form
due to incorrect configuration. Temporary Layer 2 loops can also form during
convergence after a change in the network topology.
The PE routers run the BGP path selection procedure on locally originated and received
Layer 2 route advertisements to establish that the routes are suitable for advertisement
to other peers, such as BGP route reflectors. If a PE router in a VPLS network is also a
route reflector, the path selection process for the multihomed site has no effect on the
path selection process performed by this PE router for the purpose of reflecting Layer 2
routes. Layer 2 prefixes that have different route distinguishers are considered to have
different NLRIs for route reflection. The VPLS path selection process enables the route
reflector to reflect all routes that have different route distinguishers to the route reflector
clients, even though only one of these routes is used to create the VPLS pseudowire to
the multihomed site.
Junos OS supports VPLS multihoming for both FEC 128 and FEC 129. Support for FEC
129 is added in Junos OS Release 12.3.
Configuring VPLS Multihoming (FEC 128) on page 1268
Advantages of Using Autodiscovery for VPLS Multihoming
Example: Configuring VPLS Multihoming (FEC 129)
We recommend that you configure unique route
To prevent the formation of Layer 2 loops between the CE
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