Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 53)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 29
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RSVP soft preemption
1
Pruning
The process of removing egress LSRs from an existing P2MP LSP is known as pruning. It allows
removal of egress nodes from a P2MP LSP at different points in time. Pruning can be achieved
using any one of the following signaling methods:
• Implicit S2L Sub-LSP Teardown — Sending a modified Path message that includes all S2L
sub-LSPs except the one that is being pruned.
• Explicit S2L Sub-LSP Teardown — Sending a Path Tear message for the corresponding Path
message. Path Tear message contains P2MP session-object and sender template object to
uniquely identify any S2L Sub-LSP that is being pruned.
NOTE
Brocade devices support the explicit method of pruning LSRs only and do not support the implicit
method.
RSVP refresh reduction support to P2MP
RSVP refresh reduction feature support is extended to P2MP LSPs. The following refresh reduction
extensions are applicable to P2MP.
• Reliable messaging
• Guaranteed message delivery (ACK, Retransmission)
• Message bundling
• Combined multiple RSVP messages into one
• Summary refresh
RSVP soft preemption
RSVP soft preemption implements a suite of protocol modifications extending the concept of
preemption with the goal of reducing or eliminating traffic disruption of TE LSPs. It is achieved by
using additional signaling and maintenance mechanisms to alert the ingress LER of the
preemption that is pending and allows for temporary control-plane under-provisioning while the
preempted tunnel is rerouted in a non-disruptive fashion (make before-break) by the ingress LER.
During the period that the tunnel is being rerouted, link capacity is under-provisioned on the
midpoint where preemption was initiated and potentially one or more links upstream along the
path where other soft preemptions may have occurred. Soft preemption is a property of the LSP
and is disabled by default.
The default preemption in an MPLS-TE network is hard preemption. This is helpful in cases where
actual resource contention happens in the network. Soft Preemption provides flexibility for
operators to select the type of preemption based on network conditions.
MPLS soft preemption is useful for network maintenance. For example, all LSPs can be moved
away from a particular interface, and then the interface can be taken down for maintenance
without interrupting traffic. MPLS soft preemption is also useful in dynamic networks where
preemption often occurs.