In preparation for a detailed description of MPLS, here is some of the terminology used in this course:
■ Label switch router (LSR): A device that forwards packets primarily based on labels
■ Edge LSR: A device that primarily labels packets or removes labels
LSRs and edge LSRs are usually capable of doing both label switching and IP routing. Their names are based on their positions in an MPLS domain. Routers that have all interfaces enabled for MPLS are called LSRs because they mostly forward labeled packets. Routers that have some interfaces that are not enabled for MPLS are usually at the edge of an MPLS domain (autonomous system, or AS). These routers also forward packets based on IP destination addresses and label them if the outgoing interface is enabled for MPLS.
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