Various applications of MPLS make use of label stacks with multiple entries. In some cases, it is possible to replace the top label of the stack with an IP-based encapsulation, thereby enabling the application to run over networks that do not have MPLS enabled in their core routers. This document specifies two IP-based encapsulations: MPLS-in-IP and MPLS-in-GRE (Generic Routing Encapsulation). Each of these is applicable in some circumstances. [STANDARDS-TRACK]