The egress LSR requests the “popping” through the label distribution protocolĮgress LSR advertises implicit-null label The label at the top of the stack is removed (popped) by the upstream neighbor of the egress LSR Label Switch Path (LSP) Penultimate Hop Popping LSR only binds and advertise a label for a particular FEC if: The LSR then advertises the Label to its neighbor
LSR binds a Label to a FEC independently, whether or not the LSR has received a Label the next-hop for the FEC LSR discards all labels for FECs without next-hop Improve convergence time, when next-hop is again available after IP convergence Next-hop address is the downstream neighborĭownstream LSRs distribute labels upon request LSRs know their downstream neighbors through the IP routing protocol Rtr-B is the downstream neighbor of Rtr-A for destination 171.68.10/24 Rtr-C is the downstream neighbor of Rtr-B for destination 171.68.10/24 Labels are assigned and exchanged between adjacent neighboring LSRĪpplications may require non-adjacent neighbors MPLS LSRs always forward packets based on the value of the label at the top of the stackĠ 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
More than one Label is allowed -> Label Stack The egress LSR removes the label before forwarding the The ingress LSR receives IP packets, performs packet classification, assign a label, and forward the labelled packet into the MPLS networkĬore LSRs switch packets/cells based on the label value Packet forwarding is done based on LabelsĪn IP routing protocol is used within the routing domain (e.g.:OSPF, i-ISIS)Ī label distribution protocol is used to distribute address/label mappings between adjacent neighbors MPLS forwarding is done in the same way as in ATM switches
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