4.1 Motivations for MPLS label distribution Migrations

Foundations for successful deployment of MPLS-based applications have not only been integrating MPLS with other protocols such as an IGP or BGP, but also the election of the correct strategy for MPLS label allocation and distribution. Those topics have been addressed since the very early origins of MPLS.

[RFC3035], [RFC3036] (made obsolete by [RFC5036]), and [RFC3037] soon advocated the concept of a brand new Label Distribution Protocol (LDP). This new protocol was exclusively defined to distribute MPLS label bindings with a set of mechanisms by which Label-Switched Paths (LSPs) may get established by mapping Forwarding Equivalence Classes (FECs) to MPLS label bindings. LDP included several discovery procedures as well, so that not only directly connected peers, but also, by means of an extended discovery mechanism based on LDP targeted hellos, distant LSRs could set up an LDP session. This machinery has been the cornerstone for many MPLS-based applications and needs to be considered carefully for migration purposes.