Alcatel-Lucent 7450 Manual page 266

MPLS Commands
Parameters
group-name — Specifies admin groups to be included when an LSP is set up.
priority
Syntax priority setup-priority hold-priority
no priority
Context config>router>mpls>lsp>primary
config>router>mpls>lsp>secondary
Description This command enables the soft pre-emption procedures for this LSP path. The operator enables the
soft pre-emption mechanism on a specific LSP name by explicitly configuring the setup and holding
priorities for the primary path at the 7x50 head-end node. The operator can similarly configure
priority values for a secondary path for this LSP name. Different values could be used for the primary
and for any of the secondary paths. In the absence of explicit user configuration, the setup priority is
internally set to the default value of 7 and the holding priority is set to the default value of 0. Note
however that valid user-entered values for these two parameters require that the holding priority be
numerically lower than or equal to the setup priority, otherwise pre-emption loops can occur.
Pre-emption is effected when a 7x50 pre-empting node processes a new RSVP session reservation
and there is not enough available bandwidth on the RSVP interface, or the Class Type (CT) when
Diff-Serv is enabled, to satisfy the bandwidth in the Flowspec object while there exist other session
reservations for LSP paths with a strictly lower holding priority (numerically higher holding priority
value) than the setup priority of the new LSP reservation. If enough available bandwidth is freed on
the link or CT to accommodate the new reservation by pre-empting one or more lower priority LSP
paths, the pre-empting node allows temporary overbooking of the RSVP interface and honors the
new reservation.
The 7x50 pre-empting node will immediately set the 'Preemption pending' flag (0x10) in the IPv4
Sub-Object in the RRO object in the Resv refresh for each of the pre-empted LSP paths. The IPv4
Sub-Object corresponds to the outgoing interface being used by the pre-empting and pre-empted LSP
paths. Note however that the bandwidth value in the Flowspec object is not changed. The Resv flag
must also be set if the pre-empting node is a merge point for the primary LSP path and the backup
bypass LSP or detour LSP and the backup LSP is activated.
When evaluating if enough available bandwidth will be freed, the 7x50 pre-empting node considers
the reservations in order from the lowest holding priority (numerically higher holding priority value)
to the holding priority just below the setup priority of the new reservation. A new reservation cannot
pre-empt a reservation which has a value of the holding priority equal to the new reservation setup
priority.
When Diff-Serv is enabled on the pre-empting node and the MAM bandwidth allocation model is
used, a new reservation can only pre-empt a reservation in the same Class Type (CT).
LSP paths which were not flagged at the head-end for soft pre-emption will be hard pre-empted. LSP
paths with the default holding priority of 0 cannot be pre-empted. LSP paths with zero bandwidth do
not pre-empt other LSP paths regardless of the values of the path setup priority and the path holding
priority. They can also not be pre-empted.
When evaluating if enough available bandwidth will be freed, the 7x50 pre-empting node considers
the reservations in order from the lowest holding priority (numerically higher holding priority) to the
holding priority just below the setup priority of the new reservation. There is no specific order in
which the reservations in the same holding priority are considered. Furthermore, LSP paths which
Page 266 7450 ESS MPLS Guide