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the label for the outgoing packet
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For example, consider the `label forwarding table` of a network node below.
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index
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outgoing interface
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label
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South
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7
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1
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none
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2
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West
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3
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East
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If this node receives a packet with `label=2`, it forwards the packet on its `West` interface and sets the `label` of the outgoing packet to `2`. If the received packet's `label` is set to `3`, then the packet is forwarded over the `East` interface and the `label` of the outgoing packet is set to `2`. If a packet is received with a label field set to `1`, the packet is discarded since the corresponding `label forwarding table` entry is invalid.
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`Label switching` enables a full control over the path followed by packets inside the network. Consider the network below and assume that we want to use two virtual circuits : `R1->R3->R4->R2->R5` and `R2->R1->R3->R4->R5`.
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->R2
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->R5
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Since a packet received with `label=1` must be forwarded to `R5` with `label=1`, `R2`'s `label forwarding table` could contain :
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Two virtual circuits pass through `R3`. They both need to be forwarded to `R4`, but `R4` expects `label=1` for packets belonging to the virtual circuit originated by `R2` and `label=0` for packets belonging to the other virtual circuit. `R3` could choose to leave the labels unchanged.
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->R4
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