RFC 3037 (rfc3037) - Page 2 of 7
LDP Applicability
Alternative Format: Original Text Document
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