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How does the LSR know which is the top label, bottom label, and a middle label of the label stack?

April 26, 2017Label LSR middle stack

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How does the LSR know which is the top label, bottom label, and a middle label of the label stack?

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A. The label immediately after the Layer 2 header is the top label, and the label with the S bit set to 1 is the bottom label. No application requires LSR to read/identify the middle labels. However, a label will be a middle label if it is not at the top of the stack and the S bit is set to 0.