Final answer:
The size of an MPLS header is 32 bits, which includes a 20-bit label value, a 3-bit Traffic Class field, a 1-bit Bottom of Stack flag, and an 8-bit TTL field. The correct answer is D.
Step-by-step explanation:
The size of an MPLS (Multiprotocol Label Switching) header is d. 32 bits. MPLS is a data-carrying technique for high-performance telecommunications networks that directs data from one node to the next based on short path labels rather than long network addresses, thus avoiding complex lookups in a routing table and speeding up traffic flows.
The MPLS header, also known as an MPLS label stack entry, contains four fields: a 20-bit label value, a 3-bit Traffic Class field for Quality of Service (QoS) priority (formerly known as the Experimental field), a 1-bit Bottom of Stack flag to indicate if it’s the last label in the stack, and an 8-bit Time-to-Live (TTL) field. Altogether, these comprise a 32-bit MPLS header that is inserted between the Layer 2 (Data Link layer) and Layer 3 (Network layer) headers in the OSI model when the packet is on an MPLS network.
MPLS networks are widely used by Internet service providers and in enterprise networks. This technology enables more efficient and scalable networks, as it can provide a way to create end-to-end circuits across any type of transport medium, using any protocol. It also supports traffic engineering, enabling network operators to direct flows across various paths based on current network utilization.