This feature allows encapsulating (and decapsulating) L2 traffic from a given interface or subinterface over a GRE tunnel. An MPLS label is added to identify the ingress interface (similar to MPLS pseudowires) and the GRE tunnel is used to transport the packets to a remote endpoint.

This feature allows users to preserve IP TTL and MPLS EXP (also known as TC) value on MPLS routers, as well as add a user-specified TTL/EXP value when pushing new MPLS labels in pipe mode.