Alcatel-Lucent 7450 Manual page 267

were not flagged at the head-end for soft pre-emption cannot be pre-empted because their holding
priority is set internally to 0.
The 7x50 pre-empting node starts a preemption timer for each of the pre-empted LSP paths. While
this timer is on, the node should continue to refresh the Path and Resv for the pre-empted LSP paths.
When the preemption timer expires, the node tears down the reservation if the head-end node has not
already done so.
A 7x50 head-end node upon receipt of the Resv refresh message with the 'Preemption pending' flag
must immediately perform a make-before-break on the affected adaptive CSPF LSP. Both IGP metric
and TE metric based CSPF LSPs are included. If an alternative path that excludes the flagged
interface is not found, then the LSP is put on a retry in a similar way to the Global Revertive
procedure at a 7x50 head-end node. However, the number of retries and the retry timer are governed
by the values of the retry-limit and retry-timer parameters: config>router>mpls>lsp>retry-limit;
config>router>mpls>lsp>retry-timer.
Note that MPLS will keep the address list of flagged interfaces for a maximum of 60 seconds (not
user-configurable) from the time the first Resv message with the 'Preemption pending' flag is
received. This actually means that MPLS will request CSPF to find a path that excludes the flagged
interfaces in the first few retries until success or until 60 seconds have elapsed. Subsequent retries
after the 60 seconds will not exclude the flagged interfaces as it is assumed IGP has converged by
then and the Unreserved Bandwidth sub-TLV for that priority, or TE Class, in the TE database will
show the updated value taking into account the pre-empting LSP path reservation or a value of zero if
overbooked.
If the LSP has a configured secondary standby which is operationally UP, the 7x50 will switch the
path of the LSP to it and then start the MBB. If no standby path is available and a secondary non-
standby is configured, the 7x50 will start the MBB and signal the path of the secondary. The LSP path
will be switched to either the secondary or the new primary, whichever comes up first.
The no form of the command reverts the LSP path priority to the default values and results in setting
the setup priority to 7, in setting the holding priority to 0, and in clearing the 'soft preemption desired'
flag in the RRO in the Resv refresh message.
Default no priority.
Parameters
setup-priority — The priority of the reservation for this session at setup time.
holding-priority — The priority of the reservation for this session at pre-emption action.
7450 ESS MPLS Guide
Values 0 — 7 (0 is the highest priority and 7 is the lowest priority.)
Default 7 — This session does not pre-empt any other session.
Values 0 — 7 (0 is the highest priority and 7 is the lowest priority.)
Default
0 — This session does not get pre-empted by any other session.
MPLS and RSVP
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