Operation Manual – MPLS TE
H3C S9500 Series Routing Switches
Chapter 1 MPLS TE Configuration
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Traffic characteristics
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Preemption
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Route pinning
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Administrative group and affinity attribute
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Reoptimization
I. Strict and loose explicit routes
An LSP is called a strict explicit route if all LSRs along the LSP are specified.
An LSP is called a loose explicit route if the downstream LSR selection conditions
rather than LSRs are defined.
II. Traffic characteristics
Traffic is described in terms of peak rate, committed rate, and service granularity.
The peak and committed rates describe the bandwidth constraints of a path while the
service granularity specifies a constraint on the delay variation that the CR-LDP MPLS
domain may introduce to a path's traffic.
III. Preemption
CR-LDP signals the resources required by a path on each hop of the route. If a route
with sufficient resources cannot be found, existing paths may be rerouted to reallocate
resources to the new path. This is called path preemption.
Two priorities, setup priority and holding priority, are assigned to paths for making
preemption decision. Both setup and holding priorities range from 0 to 7, with a lower
numerical number indicating a higher priority.
For a new path to preempt an existing path, the setup priority of the new path must be
greater than the holding priority of the existing path. To initiate a preemption, the RESV
message of RSVP-TE is sent.
To avoid flapping caused by improper preemptions between CR-LSPs, the setup
priority of a CR-LSP should not be set higher than its holding priority.
IV. Route pinning
Route pinning prevents an established CR-LSP from changing upon route changes.
If a network does not run IGP TE extension, the network administrator will be unable to
identify from which part of the network the required bandwidth should be obtained when
setting up a CR-LSP. In this case, loose explicit route (ER-hop) with required resources
is used. The CR-LSP thus established however, may change when the route changes,
for example, when a better next hop becomes available. If this is undesirable, the
network administrator can set up the CR-LSP using route underpinning to make it a
permanent path.
