Juniper EX9200 Features Manual page 97

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Copyright © 2016, Juniper Networks, Inc.
When a PE router receives all of the available paths to each CE device, it runs the
designated forwarder path selection algorithm to select the preferred path to reach
each CE device, independently of the results of the earlier BGP path selection algorithm
run on the Provider router. The VPLS designated forwarder algorithm uses the D-bit,
preference, and PE router identifier to determine which of the valid paths to each CE
device to use. The PE router might select a path to reach a CE device which is different
from the path selected by the BGP-based Provider routers. In this scenario, the following
is the expected behavior for traffic sent to the multihomed CE device:
If the path selected by the remote PE router is available, traffic will traverse the
network to the multihomed CE device using the remote PE router's preferred path
(again, ignoring the path selected by the BGP-based Provider routers).
If the path selected by the remote PE router fails:
The Provider routers switch the traffic destined for the multihomed CE device to
1.
the alternate path as soon as failure is detected.
The Provider routers notify the remote PE routers of the path failure.
2.
The remote PE routers update their routing tables accordingly.
3.
For more information about the VPLS designated forwarder path selection algorithm,
see "VPLS Path Selection Process for PE Routers" on page
described in the Internet draft draft-kompella-l2vpn-vpls-multihoming-03.txt,
Multi-homing in BGP-based Virtual Private LAN Service.
To enable the BGP path selection algorithm for Layer 2 VPN and VPLS routing instances,
complete the following steps:
Run Junos OS Release 12.3 or later on all of the PE and Provider routers participating
1.
in Layer 2 VPN or VPLS routing instances.
Attempting to enable this functionality on a network with a mix of routers that both
do and do not support this feature can result in anomalous behavior.
Specify a unique route distinguisher on each PE router participating in a Layer 2 VPN
2.
or VPLS routing instance.
Configure the
3. l2vpn-use-bgp-rules
participating in Layer 2 VPN or VPLS routing instances.
You can configure this statement at the
level to apply this behavior to all of the routing instances on the router or at the
routing-instances routing-instance-name protocols bgp path-selection]
to apply this behavior to a specific routing instance.
Understanding BGP Path Selection
VPLS Path Selection Process for PE Routers on page 57
VPLS Feature Guide for EX9200 Switches
l2vpn-use-bgp-rules
Chapter 9: Configuring BGP Path Selection for Layer 2 VPNs
57. This algorithm is also
statement on all of the PE and Provider routers
[edit protocols bgp path-selection] hierarchy
[edit
hierarchy level
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