Label stacking is the encapsulation of an MPLS packet inside another MPLS packet – that is, adding an MPLS header “on top of” (hence stacking) an existing MPLS header. The result of stacking is the ability to tunnel one MPLS LSP inside another LSP.

How does MPLS label work?

What is the “label switching” in MPLS routing? As packets travel through the MPLS network, their labels are switched or swapped. The packet enters the edge of the MPLS backbone, is examined, classified and given an appropriate label, and forwarded to the next hop in the pre-set Label Switched Path (LSP).

How many labels are used in MPLS?

An MPLS transit router has no such requirement. Usually (by default with only one label in the stack, accordingly to the MPLS specification), the last label is popped off at the penultimate hop (the hop before the egress router).