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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, 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 or reallocating network resources. You can 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 traverse. If a better
route is found for an existing CR-LSP, a new CR-LSP is established to replace the old one, and services are
switched to the new CR-LSP.

RSVP-TE

Two QoS models are available: IntServ and 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.
RSVP features:
Unidirectional.
Receiver oriented. The receiver initiates resource reservation requests and is responsible for
maintaining the reservation information.
Using soft state mechanism to maintain resource reservation information.
Extended RSVP can support MPLS label distribution and allow resource reservation information to be
transmitted with label bindings. This extended RSVP is called "RSVP-TE," which is operating as a
signaling protocol for LSP tunnel setup in MPLS TE.
Basic concepts
Soft state
Soft state is a mechanism used in RSVP-TE to periodically refresh the resource reservation state on
a node. The resource reservation state includes the path state and the reservation state. The path
state is generated and refreshed by the Path message. The reservation state is generated and
refreshed by the Resv message. A state is to be removed if no refresh messages are received for it
in certain interval.
Resource reservation style
Each LSP set up using RSVP-TE is assigned a resource reservation style. During an RSVP session, the
receiver decides which reservation style to use for this session and which LSPs to use.
The following reservation styles are available:
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Troubleshooting

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