CR-LDP (Contraint-based Routing LDP)

Before discussing the CE-LDP, lets explaint “constraint-based routing” term.

“Contraint-based Routing” is the routing which in which the routing process is done according to some constraints. Both QoS-based routing and policy-based routing belong to Contraint-based Routing. As you know these routing include QoS constraints or policy constraints.

CR-LDP (constraint-based LDP) contains extensions for LDP. And with these extensions, Contraint-based Routing is supported on LDP. In other words, Contraint-based Routing brings Traffic Engineering(TE) mechanism to the LDP.

The additional TLV parameters are new for CR-LDP:

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


For more information about LDP, T-LDP and CR-LDP, check the related following RFCs...

RFC 5036: LDP Specification
RFC 3815: Definitions of Managed Objects for the MPLS,LDP
RFC 3478: Graceful Restart Mechanism for Label Distribution Protocol
RFC 5443: LDP IGP Synchronization
RFC 7307: LDP Extensions for Multi-Topology
RFC 7361: LDP Extensions for Optimized MAC Address Withdrawal in a H-VPLS
RFC 3212: Constraint-Based LSP Setup using LDP
RFC 3213: Applicability Statement for CR-LDP 
RFC 3214: LSP Modification Using CR-LDP