2. A host computer with an IP address of 172.16.29.155 using a subnet mask of 255.255.255.0 and a gateway of 172.16.29.1 pings a computer with an IP address of 172.16.29.83. Will 172.16.29.155 send an ARP request broadcast for 172.16.29.83?

From the host IP address and subnet mask, you can tell that both computers are on the same network. Host 172.16.29.155 will need to send an ARP request broadcast for 172.16.29.83 to get the MAC address and update its ARP table if the host 172.16.29.83 has not already done so.

Explanation:

Address Resolution Protocol (ARP) is a procedure for mapping a logical address known as the IP address to a physical address known as MAC (Media Access Control) address in a local area network. The job of the ARP is essentially to translate 32-bit addresses to 48-bit addresses and vice-versa when using IP Version 4 (IPv4) to communicate on the network.

Most of the computer programs/applications use logical address (IP address) to send/receive messages, however, the actual communication happens over the physical address (MAC address) this happens in the layer 2 of the OSI model. An ARP request is a broadcast, and an ARP response is a Unicast.

Scenarios when ARP is used:

Scenario-1: The sender is a host and wants to send a packet to another host on the same network.

·        Use ARP to find another host’s physical address

Scenario -2: The sender is a host and wants to send a packet to another host on another network.

·        Sender looks at its routing table.

·        Find the IP address of the next-hop (router) for this destination.

·        Use ARP to find the router’s physical address

Scenario -3: the sender is a router and received a datagram destined for a host on another network.

·        Router checks its routing table.

·        Find the IP address of the next router.

·        Use ARP to find the next router’s physical address.

Scenario -4: The sender is a router that has received a datagram destined for a host in the same network.

·        Use ARP to find this host’s physical address.

The situation in the question above falls under scenario-1. From the host IP address and subnet mask, you can tell that both computers are on the same network. Host 172.16.29.155 will need to send an ARP request broadcast for 172.16.29.83 so to get the MAC address and update its ARP table if the host 172.16.29.83 has not already done so.