Monday, April 9, 2012

MPLS OPERATION


  • Unlabeled packet enter into the service provider network via PE router.
  • PE router add label impose a label to the unlabeled packet & then forward to the P router(also known as LSR) along the Label Switch Path(LSP) in the core network of service provider.
  • In the core network of service provider each P routers forward the packet by swapping the labels along the LSR learned by protocol LDP.
  • At other end when leaving service provider network PE router (also known as Edge-LSR) pops the label by mechanism called Penultimate Hop Popping.
  • Penultimate meaning is "next to last"
  • last hop in the service provider network must
    • look up MPLS label
    • POP MPLS label
    • Look for IPv4 destination
  • PHP avoids extra look up for MPLS label on last hop
  • For this implict NULL label was advertised
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