At which OSI boundary is an MPLS label inserted?
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Correct answer: between Layer 2 and Layer 3.
Why this is the answer
MPLS operates at a layer often referred to as "Layer 2.5" because it inserts its label header between the Layer 2 (Data Link) frame header and the Layer 3 (Network) IP packet header. This placement allows MPLS to forward packets based on labels, independent of the Layer 3 IP header, providing benefits like faster forwarding and traffic engineering. If it were between Layer 5 and Layer 6, it would be too high in the stack to influence network-level forwarding. If between Layer 1 and Layer 2, it would be part of the physical or data link layer, which is not its function. If between Layer 3 and Layer 4, it would be above the network layer, negating its purpose of enhancing network-layer forwarding.
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