Similarly, when a label is pushed onto a packet that already has a label, the EXP value from the underlying label is copied into the EXP field of the newly imposed label. This is known as the mpls2mpls path.

Three actions are possible in the mpls2mpls path:

• Push— An mpls2mpls push is when one or more labels are added to an already-labeled packet.

• Swap— An mpls2mpls swap is when the topmost label on a packet is swapped for another label.

• Pop— An mpls2mpls pop is when one or more labels are removed from a packet, but at least one label is left.

Figure 6-3 illustrates these three cases.

Figure 6-3. mpls2mpls Operations

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