Summary

In this chapter, you have seen what a label is and that labels can be stacked in a label stack. The label stack sits in front of the transported packet. If the transported packet is an IP packet, the label stack is behind the Layer 2 header but before the IP header.

You have seen how the labels are switched at each LSR in the MPLS network, thus providing label switching. An ordered sequence of LSRs is a label switched path (LSP). A Forwarding Equivalence Class (FEC) is a group or flow of packets that receive the same forwarding treatment throughout the MPLS network. The FEC is thus determined by the label stack and the EXP bits in the label. A distribution protocol is needed to distribute the labels between LSRs in the MPLS network. ...

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