MPLS Unicast IP Routing Architecture Cont



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The figure shows a scenario where IP packets are successfully forwarded by using the FIB table.

Labeled packets, on the other hand, are not forwarded due to a lack of information in the LFIB table. Normal MPLS functionality prevents the forwarding from happening, because no adjacent router is going to use a label unless this router previously advertised it.

The example simply illustrates that label switching tries to use the LFIB table only if the incoming packet is labeled, even if the destination address is reachable by using the FIB table.

Note The LIB table will hold all locally generated labels by a label switch router (LSR). The LFIB

table contains labels that are used to switch packets.

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