Juniper EX9200 Features Manual page 76

VPLS Feature Guide for EX9200 Switches
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If the router IDs are the same, the routes are from the same PE router and the
4.
advertisement is considered to be an update. The router ID corresponds to the value
of the originator ID for the BGP attribute (if present). Otherwise, the IP address for the
remote BGP peer is used.
If the block offset values are the same, the advertisement is considered to be an
5.
update.
Once the VPLS path selection process has been completed and the designated VE device
has been selected, a pseudowire is signaled between the remote PE router and the local
PE router.
NOTE: The VPLS path selection process works the same whether or not the
route has been received from another PE router, a route reflector, or an
autonomous system border router (ASBR).
When the remote PE router establishes or refreshes a pseudowire to the local PE router,
it verifies that the prefix is in the range required for the site ID based on the block offset
and label range advertised by the designated VE device. If the prefix is out of range, the
pseudowire status is set to out of range.
The following cases outline the potential decisions that could be made when a PE router
completes the VPLS path selection process for a Layer 2 advertisement in the VPLS
network:
The PE router originated one of the advertisements and selected its own advertisement
as the best path.
This PE router has been selected as the designated VE device. Selection as the
designated VE device triggers the creation of pseudowires to and from the other PE
routers in the VPLS network. If the remote customer site is multihomed, the designated
VE device triggers the creation of pseudowires to and from only the designated VE
device for the remote site.
The PE router originated one of the advertisements but did not select its own
advertisement as the best path.
This PE router is a redundant PE router for a multihomed site, but it was not selected
as the designated VE device. However, if this PE router has just transitioned from being
the designated VE device (meaning it was receiving traffic from the remote PE routers
addressed to the mulithomed customer site), the PE router tears down all the
pseudowires that it had to and from the other PE routers in the VPLS network.
The PE router received the route advertisements and selected a best path. It did not
originate any of these advertisements because it was not connected to the customer
site.
If the best path to the customer site (the designated VE device) has not changed,
nothing happens. If the best path has changed, this PE router brings up pseudowires
to and from the newly designated VE device and tears down the pseudowires to and
from the previously designated VE device.
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