R3303-HP HSR6800 Routers MPLS Configuration Guide

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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, 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.
Reoptimization
Traffic engineering is a process of allocating or reallocating network resources. You can configure it to
meet desired QoS.
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.
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
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.
Features of RSVP:
• 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 of RSVP-TE
Soft state—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.