Select two characteristics of MPLS labels.
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Correct answer: LDP uses TCP for reliable delivery of information., An MPLS label is a short identifier that identifies a forwarding equivalence class..
Why this is the answer
LDP (Label Distribution Protocol) uses TCP port 646 for reliable delivery of label mapping information between LDP peers. This ensures that label advertisements and withdrawals are consistently exchanged. An MPLS label is indeed a short, fixed-length identifier (20-bit) that categorizes packets into a Forwarding Equivalence Class (FEC), allowing routers to forward them based on the label rather than a complex IP lookup. The label edge router (LER) pushes or pops labels, but the label switch router (LSR) swaps labels. Labels are imposed before the Layer 3 header. While a common scenario involves one or two labels, there is no strict maximum of two labels; multiple labels can be stacked for services like VPNs or Traffic Engineering.
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