CR-LDP: Constraint-based Label Distribution Protocol Overview

CR-LDP: Constraint-based Label Distribution Protocol Overview

CR-LDP, constraint-based LDP, is one of the protocols in the MPLS architecture. CR-LDP contains extensions for LDP to extend its capabilities such as setup paths beyond what is available for the routing protocol. For instance, an LSP can be setup based on explicit route constraints, QoS constraints, and other constraints. Constraint-based routing (CR) is a mechanism used to meet Traffic Engineering requirements. These requirements are met by extending LDP for support of constraint-based routed label switched paths (CR-LSPs). Other uses for CR-LSPs include MPLS-based VPNs.

Protocol Structure - CR-LDP Constraint-based Label Distribution
CR-LDP has the same structure as LDP except the following additional TLV parameters. 

Value	Parameter
821	LSPID
822	ResCls
503	Optical Session Parameters
800	Explicit Route
801-804	ER-Hop TLVS
810	Traffic Parameters
820	Preemption
823	Route Pinning
910	Optical Interface Type
920	Optical Trail Desc
930	Optical Label
940	Lambada Set

CR-LDP is defined by IETF (http://www.ietf.org ) RFC3212.

Reference

http://www.javvin.com/protocol/rfc3031.pdf £ºMultiprotocol Label Switching Architecture
http://www.javvin.com/protocol/rfc3212.pdf £ºCR-LDP Specification