Cr-Lsp - HP HSR6800 Configuration Manual

CR-LSP

Unlike ordinary LSPs established based on routing information, CR-LSPs are established based on
criteria such as bandwidth, selected path, and QoS parameters, in addition to routing information.
The mechanism setting up and managing constraints is called Constraint-based Routing (CR).
CR-LSP uses the following concepts:
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Strict and loose explicit routes
•
Traffic characteristics
•
Preemption
•
Route pinning
•
Administrative group and affinity attribute
•
Reoptimization
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.
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.
Preemption
During establishment of a CR-LSP, if a path with sufficient resources cannot be found, the CR-LSP
can be established by preempting the resources of a lower-priority CR-LSP. This is called path
preemption.
Two priorities, setup priority and holding priority, are assigned to CR-LSPs for making preemption
decision. Both setup and holding priorities are in the range of 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 must not be set higher than its holding priority.
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 is unable to identify from
which part of the network the required bandwidth can be obtained when setting up a CR-LSP. In this
case, loose explicit route (ER-hop) with required resources is used. The established CR-LSP,
however, might 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.
Administrative group and affinity attribute
The affinity attribute of an MPLS TE tunnel identifies the properties of the links that the tunnel can
use. Together with the link administrative group, it decides which links the MPLS TE tunnel can use.
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