Constraint-based Routing Label Distribution Protocol

{{Short description|Computer network control protocol}}

{{Refimprove|date=December 2014}}

Constraint-based Routing Label Distribution Protocol (CR-LDP) is a control protocol used in some computer networks.

As of February 2003, the IETF MPLS working group deprecated CR-LDP and decided to focus purely on RSVP-TE.{{cite journal |title=The Multiprotocol Label Switching (MPLS) Working Group decision on MPLS signaling protocols |author1=L. Andersson|author2=G. Swallow |rfc=3468 |date=February 2003 |page=6 |doi=10.17487/RFC3468 }}

It is an extension of the Label Distribution Protocol (LDP), one of the protocols in the Multiprotocol Label Switching 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, a label-switched path can be set up based on explicit route constraints, quality of service 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 virtual private networks.

CR-LDP is almost same as basic LDP, in packet structure, but it contains some extra TLVs which basically set up the constraint-based LSP.