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When multiple SDPs exist between two endpoints, the tunnel manager will select the appropriate
SDP. The algorithm will prefer SDPs with the best (lower) metric. Should there be multiple SDPs
with equal metrics, the operational state of the SDPs with the best metric will be considered. If the
operational state is the same, the SDP with the higher sdp-id will be used. If an SDP with a
preferred metric is found with an operational state that is not active, the tunnel manager will flag it
as ineligible and restart the algorithm.
Automatic Instantiation of Pseudowires (SDP Bindings)
The choice of manual or auto provisioned SDPs has limited impact on the amount of required
provisioning. Most of the savings are achieved through the automatic instantiation of the
pseudowire infrastructure (SDP bindings). This is achieved for every auto-discovered VSIs
through the use of the pseudowire template concept. Each VPLS service that uses BGP AD
contains the “pw-template-bind” option defining specific layer 2 VPN parameters. This command
references a “pw-template” which defines the pseudowire parameters. The same “pw-template”
may be referenced by multiple VPLS services. As a result, changes to these pseudowire templates
have to be treated with great care as they may impact many customers at once.
The Alcatel-Lucent implementation provides for safe handling of pseudowire templates. Changes
to the pseudowire templates are not automatically propagated. Tools are provided to evaluate and
distribute the changes. The following command is used to distribute changes to a “pw-template” at
the service level to one or all services that use that template.
PERs-4# tools perform service id 300 eval-pw-template 1 allow-service-impact
If the service ID is omitted, then all services will be updated. The type of change made to the “pw-
template” will influence how the service is impacted.
1. Adding or removing a split-horizon-group will cause the router to destroy the original object
and recreate using the new value.
2. Changing parameters in the vc-type {ether | vlan} command requires LDP to re-signal the
labels.
Both of these changes are service affecting. Other changes will not be service affecting.
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