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What is an upstream label switch router (LSR)? What is a downstream LSR?

April 26, 2017Downstream Label LSR Router Switch upstream

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What is an upstream label switch router (LSR)? What is a downstream LSR?

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A. Upstream and downstream are relative terms in the MPLS world. They always refer to a prefix (more appropriately, an FEC). These examples further explain this. mpls-downstrmA.jpg For FEC 10.1.1.0/24, R1 is the “Downstream” LSR to R2. For FEC 10.1.1.0/24, R2 is the “Upstream” LSR to R1. mpls-downstrmB.jpg For FEC 10.1.1.0/24, R1 is the “Downstream” LSR to R2. And, R2 is the “Downstream” LSR to R3. mpls-downstrmC.jpg For FEC 10.1.1.0/24, R1 is the “Downstream” LSR to R2. For FEC 10.2.2.0/24, R2 is the “Downstream” LSR to R1. Data flows from upstream to downstream to reach that network (prefix). mpls-downstrmD.jpg The R4 routing table has R1 and R2 as the “next-hops” to reach 10.1.1.0/24.