4.1.a Implement and troubleshoot MPLS operations

from: http://www.cisco.com/en/US/tech/tk436/tk428/technologies_q_and_a_item09186a00800949e5.shtml#qa4

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.

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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.

/image/gif/paws/4649/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.

/image/gif/paws/4649/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).

/image/gif/paws/4649/mpls-downstrmD.jpg

The R4 routing table has R1 and R2 as the “next-hops” to reach 10.1.1.0/24.