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Review the exhibit.
In the exhibit, which action is performed by router R4?
In the exhibit, router R4 is performing a swap action. This means that router R4 is replacing the incoming label with a new label and forwarding the packet to the next hop along the LSP. In this case, router R4 receives a packet with label 20 from router R3 and swaps it with label 30 before sending it to router R5.
The exhibit shows an example of an MPLS network with four routers: R1, R2, R3, and R4. Router R1 is the ingress PE router and router R4 is the egress PE router. Router R2 and R3 are P routers. Router R1 assigns label 10 to the packet and sends it to router R2. Router R2 swaps label 10 with label 20 and sends it to router R3. Router R3 swaps label 20 with label 30 and sends it to router R4. Router R4 removes label 30 from the packet and forwards it based on its IP header or another label in the stack.
Therefore, the answer is D.