Bgp And Vpls Path Selection For Multihomed Pe Routers - Juniper EX9200 Features Manual

VPLS Feature Guide for EX9200 Switches

BGP and VPLS Path Selection for Multihomed PE Routers

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Alternatively, the remote PE routers could discover that the BGP next hop, represented
by the failed multihomed PE router, is unreachable. For this case, the remote PE routers
mark the Layer 2 routes advertised by the multihomed PE router as unreachable. The
remote PE routers each run the BGP and VPLS path selection procedures again and
reroute their pseudowires to the backup multihomed PE router.
The remote PE routers behave in the same manner if you reconfigure the local
preference attribute of the primary multihomed PE router (effectively performing an
administrative failover to the backup multihomed PE router). On the primary
multihomed PE router, BGP advertises a Layer 2 update with the new local preference
attribute to all of the remote PE routers. The remote PE routers each run the BGP and
VPLS path selection procedures again and reroute their pseudowires to the backup
multihomed PE router.
NOTE: In the VPLS documentation, the word router in terms such as PE router
is used to refer to any device that provides routing functions.
The BGP and VPLS path selection procedures are used to select the best path between
the remote PE router and one of the multihomed PE routers. As part of these path
selection procedures, one of the multihomed PE routers is made the designated VE
device. The designated VE device effectively acts as the endpoint for the VPLS pseudowire
from the remote PE router. Once a multihomed PE router is made the designated VE
device, a pseudowire can be created between the remote PE router and the multihomed
PE router.
NOTE: In the VPLS documentation, the word router in terms such as PE router
is used to refer to any device that provides routing functions.
Routes from multihomed PE routers connected to the same customer site share the
same site ID, but can have different route distinguishers and block offsets. On each PE
router in the VPLS network, the best path to the multihomed PE router is determined by
completing the following VE device-selection procedures on each route advertisement
received from a multihomed PE router:
BGP designated VE device-selection procedure—Runs before the VPLS designated
1.
VE device-selection procedure. However, the BGP designated VE device-selection
procedure is used only when the route distinguishers for the multihomed PE routers
are identical. If the route distinguishers are unique, only the VPLS designated VE
device-selection procedure is run.
VPLS designated VE device-selection procedure—Runs after the BGP designated VE
2.
device-selection procedure. However, if the route distinguishers for each multihomed
PE router are unique, the advertisements are not considered relevant to the BGP
designated VE device-selection procedure. As a consequence, only the VPLS
designated VE device-selection procedure is used.
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