Unicast is a type of data transmission where a message is sent from one sender to one receiver, each identified by a network address. Unicast is a one-to-one communication, as opposed to broadcast and multicast, which are one-to-many communications. Unicast is typically used for real-time data streams, such as video, audio, or online presentations, that are shared with a single user over the Internet. Unicast can also be used for email, file transfer, and other applications that require a specific recipient.  References:   Unicast - Wikipedia ,  Difference between Unicast, Broadcast and Multicast in Computer Network - GeeksforGeeks ,  Unicast Definition - TechTerms.com

The IP address 10.0.128.0/23 is a Class A private address with a subnet mask of 255.255.254.0. This means that the network prefix is 10.0.128.0 and the host identifier is the last 9 bits of the address. To find the number of IP assignable addresses, we need to subtract 2 from the total number of possible hosts, which is 29 = 512 . This is because the network address (10.0.128.0) and the broadcast address (10.0.129.255) are reserved and cannot be assigned to any host. Therefore, the number of IP assignable addresses is 512 - 2 = 510. References: IP Subnet Calculator , CIDR Calculator for IPv4 addresses , Free online IPv4 subnet calculator

The table that clients must populate to remember the L2 addressing of their neighbors is the ARP table.  ARP stands for Address Resolution Protocol, which is a protocol that maps an IP address to a MAC address 1 .  A MAC address is a unique identifier for a network interface card (NIC) that operates at the data link layer (layer two) of the OSI model 2 .  An IP address is a logical identifier for a device that operates at the network layer (layer three) of the OSI model 3 . When a client wants to communicate with another device on the same network, it needs to know the MAC address of the destination device. To do this, the client sends an ARP request, which is a broadcast message that asks “Who has this IP address?” The device that has the matching IP address replies with an ARP reply, which contains its MAC address. The client then stores this information in its ARP table, which is a cache of IP-to-MAC mappings. Therefore, statement B is correct. Statements A, C, and D are incorrect because they describe different types of tables. A MAC table is a table that a switch uses to store MAC addresses and the corresponding ports that they are connected to. A routing table is a table that a router uses to store the destination networks and the next-hop addresses that they are reachable through.  An ethernet table is not a valid term in networking.  References:   1 : Aruba Certified Network Technician (ACNT) Study Guide, page 34 2 : Aruba Certified Network Technician (ACNT) Study Guide, page 28 3 : Aruba Certified Network Technician (ACNT) Study Guide, page 29. : Aruba Certified Network Technician (ACNT) Study Guide, page 35. : Aruba Certified Network Technician (ACNT) Study Guide, page 30. : Aruba Certified Network Technician (ACNT) Study Guide, page 31.

The PCs are not able to successfully establish bidirectional communication because they are on different subnets and their default gateways are not configured correctly. The default gateway is the IP address of the router interface that connects to the same subnet as the PC. The default gateway allows the PC to send packets to destinations outside its own subnet. In this case, PC-1 and PC-2 are on the 172.16.30.0/24 and 172.16.31.0/24 subnets respectively, and the router interfaces are 172.16.30.254 and 172.16.31.254 respectively. Therefore, the correct default gateway for PC-1 is 172.16.30.254 and the correct default gateway for PC-2 is 172.16.31.254.  Changing PC-2’s default gateway to 172.16.31.254 will enable the communication between PC-1 and PC-2 1 2   References:

Aruba Certified Network Technician (ACNT) - HPE Certification and Learning

Aruba Certified Network Technician (ACNT) - Aruba Networks .

Layer 2 encapsulation is the process of adding a header and a trailer to the data coming from the upper layer (Layer 3) before sending it over the physical medium. The header and the trailer contain information such as source and destination MAC addresses, error detection, and protocol type. The devices that perform Layer 2 encapsulation are usually switches, bridges, or network interface cards (NICs). In the given network diagram, the PC is sending a message to the server. The PC first adds a Layer 2 header and trailer to the data and sends it to Switch-1. Switch-1 performs Layer 2 encapsulation again before forwarding it to the router. The router operates at Layer 3 and does not perform Layer 2 encapsulation. It only removes the Layer 2 header and trailer, checks the destination IP address, and forwards the packet to the next hop. The packet then reaches Switch-2, where Layer 2 encapsulation occurs again before it is sent to the server. The server also performs Layer 2 de-encapsulation by removing the header and trailer and passing the data to the upper layer. Therefore, the devices that have performed Layer 2 encapsulation by the time the message arrives at the server are Switch-1 and Switch-2.  References:   Understanding Data Link Layer Encapsulation ,  How Data Encapsulation & De-encapsulation Works? ,  HDLC Protocol and Encapsulation method Explained

ARP is a protocol that maps an IP address to a MAC address, which is the physical address of a device on a network. ARP is necessary because the software address (IP address) of the host or computer connected to the network needs to be translated to a hardware address (MAC address). Without ARP, a host would not be able to figure out the hardware address of another host. ARP works by sending a broadcast message to all devices on the network, asking for the MAC address of the device that has a specific IP address. The device that has that IP address replies with its MAC address, and the sender stores this information in its ARP cache for future use. The sender then uses the MAC address as the destination address of the Layer 2 header that encapsulates the IP packet. The Layer 2 header is also known as the data link layer header, which is responsible for delivering the packet to the correct device on the same network. The Layer 3 header is also known as the network layer header, which is responsible for routing the packet to the correct network.  Therefore, the correct answer is C, because ARP is used to discover the destination address of the Layer 2 header that encapsulates IP packets 1 2 3 4   References:   What Is Address Resolution Protocol (ARP)? - Fortinet ,  Address Resolution Protocol - Wikipedia ,  ARP (Address Resolution Protocol) explained - Study-CCNA ,  Aruba Certified Network Technician Exam HPE3-U01 Actual Questions

The management plane is the logical path of all traffic related to the management of the device. Examples of protocols processed in the management plane are Simple Network Management Protocol (SNMP), Telnet, HTTP, Secure HTTP (HTTPS), and SSH.  These management protocols are used for monitoring and for command-line interface (CLI) access 1 2 . Therefore, HTTPS and SSH are protocols that operate on the management plane, while the other options are not.  TCP is a transport layer protocol that provides reliable data delivery for various applications, but it is not specific to the management plane 3 .  ARP is a network layer protocol that resolves IP addresses to MAC addresses, but it is not used for device management 4 .  STP is a data link layer protocol that prevents loops in switched networks, but it is not related to the management plane 5 .  References:   1 :  Management Plane Protection - Cisco   2 :  Planes of Operation > IP Routing on Cisco IOS, IOS XE, and IOS XR: How …   3 : [Transmission Control Protocol - Wikipedia]  4 : [Address Resolution Protocol - Wikipedia]  5 : [Spanning Tree Protocol - Wikipedia] : https://en.wikipedia.org/wiki/Transmission_Control_Protocol : https://en.wikipedia.org/wiki/Address_Resolution_Protocol : https://en.wikipedia.org/wiki/Spanning_Tree_Protocol

Full-duplex is a switchport feature that allows simultaneous transmission and reception of data on a link, without causing collisions. Collisions occur when two devices try to send data at the same time on a shared medium, such as a half-duplex link or a hub. Full-duplex eliminates the need for collision detection and avoidance mechanisms, such as CSMA/CD, and increases the effective bandwidth of the link. Full-duplex requires both ends of the link to support and be configured for full-duplex mode. If one end is configured for full-duplex and the other for half-duplex, the result is a duplex mismatch, which causes performance issues and errors. Auto speed is a switchport feature that allows the switch to negotiate the speed of the link with the connected device, such as 10 Mbps, 100 Mbps, or 1000 Mbps. VLANs are logical groups of devices that share the same broadcast domain, regardless of their physical location or connection. VLANs can reduce collisions by segmenting the network and limiting the scope of broadcasts. However, VLANs alone do not prevent collisions on a link, as they depend on the duplex mode of the switchport. Half-duplex is a switchport feature that allows only one direction of data transmission at a time on a link, either sending or receiving. Half-duplex requires collision detection and avoidance mechanisms, such as CSMA/CD, to coordinate the access to the shared medium. Half-duplex reduces the effective bandwidth of the link by half, as only one device can use the link at a time. Half-duplex can cause collisions if two devices try to send data at the same time on the same link.  References:

Aruba Certified Network Technician (ACNT) | HPE Aruba Networking

Aruba Documentation Portal

switch port collisions - Cisco Community

Why is a switch port a collision domain? - Cisco Community