H3C Technologies H3C SR8800 - Manual (Page 55)

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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.
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.
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.
Reoptimization
Traffic engineering is a process of allocating/reallocating network resources. You may configure it to
meet desired QoS.
Normally, service providers use some mechanism to optimize CR-LSPs for best use of network resources.
They can do this manually but CR-LSP measurement and tuning are required. Alternatively, they can use
MPLS TE where CR-LSPs are dynamically optimized.
Dynamic CR-LSP optimization involves periodic calculation of paths that traffic trunks should traverse. If a
better route is found for an existing CR-LSP, a new CR-LSP will be established to replace the old one, and
services will be switched to the new CR-LSP.
CR-LDP
Constraint-based Routed Label Distribution Protocol (CR-LDP) is an extension to LDP. It is used in MPLS TE
to create an explicit path with resource reservation between the ingress node and the egress node.
When initiating an LSP at the ingress, CR-LDP appends some constraints in the label request message.
RSVP-TE
Overview
Currently, two QoS models are available: Integrated Service (IntServ) and Differentiated Service
(DiffServ).
Resource Reservation Protocol (RSVP) is designed for IntServ. It reserves resources on each node along a
path. RSVP operates at the transport layer but does not participate in data transmission. It is an Internet
control protocol similar to ICMP.
The following are features of RSVP:
• Unidirectional
• Receiver oriented. The receiver initiates resource reservation requests and is responsible for
maintaining the reservation information.