Where does MPLS fit in the OSI reference model?
Some might argue that MPLS does not fit in the OSI reference model. The fact that MPLS is a framework that contains enhancements to the current Layer 3 and Layer 2 technologies makes it hard to fit MPLS within one layer of the OSI model. MPLS alone cannot be considered a layer in the OSI sense as it doesn’t have a unified format for the transport of data from the layer above: it uses a shim header over SONET or Ethernet, it uses the existing VPI/VCI of ATM, etc. However, an individual MPLS function could be categorized as either an OSI Layer 3 or Layer 2 function. Does MPLS support other protocols other than IP? Yes. MPLS, by design, was meant to support many Layer 3 and Layer 2 protocols. At Layer 3, MPLS supports IPv4, IPv6, IPX, and AppleTalk. At Layer 2, MPLS supports Ethernet, PPP (for point to point links), Token Ring, FDDI, ATM, and Frame Relay. MPLS was designed to be flexible so that it could work with virtually any Layer 3 and Layer 2 technologies. How does MPLS compare to AT
