Which statement describes an MPLS LSP tunnel?
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Correct answer: unidirectional tunnel.
Why this is the answer
An MPLS LSP (Label Switched Path) tunnel is inherently unidirectional. This means that traffic flows in one direction from an ingress Label Edge Router (LER) to an egress LER. If two-way communication is required, two separate, independent LSPs are established: one for each direction. A bidirectional tunnel (and by extension, a secured bidirectional tunnel) is incorrect because MPLS LSPs are not inherently bidirectional; they are established for one-way traffic flow. A hop-by-hop tunnel is incorrect because while MPLS forwarding occurs hop-by-hop based on labels, the tunnel itself is defined as a path from ingress to egress, not as a series of independent hop-by-hop tunnels.
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