With respect to the OSI Reference model layers, which protocol is referred to as a layer 2.5 protocol?

With respect to the OSI Reference model layers, which protocol is referred to as a layer 2.5 protocol?

• MPLS
• ICMP
• PPP
• LACP 

 

EXPLANATION

MPLS is a scalable, protocol-independent transport. In an MPLS network, data packets are assigned labels. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular OSI model data link layer (layer 2) technology, such as Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous Optical Networking (SONET) or Ethernet, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. MPLS belongs to the family of packet-switched networks.
MPLS operates at a layer that is generally considered to lie between traditional definitions of OSI Layer 2 (data link layer) and Layer 3 (network layer), and thus is often referred to as a layer 2.5 protocol.

SOURCE

http://it.toolbox.com/blogs/intruder-detection/mpls-and-the-osi-reference-model-where-does-mpls-fit-in-50920