Priority queuing (PQ) is a queuing method that establishes four interface output queues that serve different priority levels: high, medium, normal, and low. Traffic in the highest priority queue will experience the least amount of jitter and delay compared to traffic in the other queues, because PQ always services the higher-priority queues first. However, this can also cause traffic in lower priority queues to be starved of bandwidth, especially if the highest priority queue is oversubscribed. Traffic in the highest priority queue is not only reserved for voice traffic, but can also include network control and routing traffic. Traffic in all queues are not always guaranteed a minimum bandwidth, because PQ does not provide any bandwidth reservation mechanism.Reference:Quality of Service (QoS) Queues and Queuing Explained,Chapter: Configuring Priority Queueing - Cisco

A reason for using VLANs in an IP network is to isolate hosts within the same IP subnet. VLANs (Virtual LANs) are logical grouping of devices in the same broadcast domain. VLANs are usually configured on switches by placing some interfaces into one broadcast domain and some interfaces into another. Each VLAN acts as a subgroup of the switch ports in an Ethernet LAN. VLANs allow network administrators to group hosts together even if the hosts are not directly connected to the same network switch.By using VLANs, hosts within the same IP subnet can be separated into different broadcast domains, which enhances security, reduces network congestion, and simplifies network management78.

An Ethernet switch will forward the frame to all ports when the destination address is FF:FF:FF:FF:FF:FF. This is because this address is the broadcast MAC address, which means that the frame is intended for all devices on the same LAN segment. The switch does not need to look up its MAC address table to find a matching entry for this address, but simply floods the frame out of all ports except the one where it received the frame. This way, the frame reaches every device on the LAN segment, regardless of their MAC addresses.Reference:Ethernet - Wireshark,Broadcast MAC Address - omnisecu.com

P routers forward packets based on the LSP label. The LSP label is the label that corresponds to the label-switched path (LSP) that is established between two PE routers in an MPLS network. The LSP label is also called the outer label or the transport label, because it is used to transport packets across the MPLS core network. P routers are also called LSRs (label switch routers) or transit routers, because they switch packets based on their labels or remove the labels. P routers do not need to look at the IP header or any other information in the packet, except for the top label in the label stack. P routers perform one of three possible operations on labels: swap, pop, or PHP (penultimate hop popping). In a swap operation, the label is swapped with a new label, and the packet is forwarded along the path associated with the new label. In a pop operation, the label is removed from the packet, and the packet is forwarded based on its IP header or another label in the stack. In a PHP operation, the label is removed from the packet at the last P router before reaching the egress PE router, and the packet is forwarded without any label to the egress PE router.

The LSP label is different from other types of labels that may be used in MPLS networks, such as VPN labels or service labels. These labels are used to identify different VPNs or services that run over MPLS networks, such as Layer 2 VPNs, Layer 3 VPNs, traffic engineering, or QoS. These labels are also called inner labels or payload labels, because they are related to the payload of the packet. These labels are not used by P routers for forwarding decisions, but only by PE routers for delivering packets to their destinations.

Therefore, the answer is C.

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.