RFC 3037 (rfc3037) - Page 2 of 7

LDP Applicability

RFC 3037                   LDP Applicability                January 2001


   This document describes the applicability of the Label Distribution
   Protocol (LDP), a new protocol for label distribution designed to
   support label distribution for MPLS forwarding along normally routed
   paths as determined by destination-based routing protocols.  This is
   sometimes called MPLS hop-by-hop forwarding.

   LDP, together with an IP routing plane and software to program ATM
   switch or Frame Relay switch cross-connect tables, can implement IP
   in a network of ATM and/or Frame Relay switches without requiring an
   overlay or the use of ATM-specific or Frame Relay-specific addressing
   or routing.

   LDP is also useful in situations that require efficient hop-by-hop
   routed tunnels, such as MPLS-based VPN architectures [RFC 2574] and
   tunneling between BGP border routers.

   In addition, LDP includes a mechanism that makes it possible to
   extend it to support MPLS features that go beyond best effort hop-
   by-hop forwarding.

   As a stand-alone protocol for distributing labels LDP does not rely
   on the presence of specific routing protocols at every hop along an
   LSP path in order to establish an LSP.  Hence LDP is useful in
   situations in which an LSP must traverse nodes which may not all
   support a common piggybacked approach to distributing labels.

   Traffic Engineering [TE] is expected to be an important MPLS
   application.  MPLS support for Traffic Engineering uses explicitly
   routed LSPs, which need not follow normally-routed (hop-by-hop)
   paths.

   Explicitly routed LSPs may be setup by CR-LDP [CRLDP-AS], a set of
   extensions to LDP, or by RSVP-TE [RSVP-TE-AS], a set of extensions to
   RSVP.  There is currently no consensus on which of these protocols is
   technically superior.  Therefore, network administrators should make
   a choice between the two based upon their needs and particular
   situation.

2. Requirement Level

   The "requirement level" [RFC 2026] for LDP is:

      Implementation of LDP is recommended for devices that perform MPLS
      forwarding along normally routed paths as determined by
      destination-based routing protocols.






Thomas & Gray                Informational