### Networking Devices and Initial Configuration Module 6.2.3 IPv4 Addressing Quiz Answers

1. Which statement describes IPv4 addressing?

• Routers use the full 32-bit IP address to determine the location of each individual host.
• The network portion of a destination IP address is obtained by performing an AND operation between a host IP address and a subnet mask.
• An IPv4 address contains two parts: a network portion and a subnet portion.
• Two hosts with the same subnet mask are in the same network.

Explanation: An IPv4 address consists of two parts: the network portion and the host portion. Routers just need to know the network portion of each IP address to forward the packet to its destination. When a router needs to identify the network portion of an IPv4 address, an AND operation is performed between the IP address and the subnet mask. The subnet mask identifies the network portion of the host IP address, not the network IP address itself, and that is why two hosts with the same subnet mask are not necessarily in the same network.

2. Which statement describes one purpose of the subnet mask setting for a host?

• It is used to describe the type of the subnet.
• It is used to identify the default gateway.
• It is used to determine to which network the host is connected.
• It is used to determine the maximum number of bits within one packet that can be placed on a particular network.

Explanation: An IPv4 address contains two portions. The network portion defines the network (or a subnet) where the host is located and the host portion identifies the host address on the network. The subnet mask is used to define the network portion of the IPv4 addressing through the logical ANDing of the IP address and the subnet mask.

3. How many octets exist in an IPv4 address?

• 4
• 8
• 16
• 32

Explanation: Each octet holds 8 bits and an IPv4 address contains 32 bits. Therefore, an IPv4 address contains four octets.

4. Which full range of decimal values are valid in one octet of an IPv4 address?

• 0 through 31
• 1 through 64
• 0 through 128
• 0 through 255
• 1 through 256

Explanation: An octet can contain 8 bits. Each bit can be a 1 or a 0 because the binary system is used. To determine the number of values that can be represented by a specific number of bits, use the formula 2x where the x represents a specific number of bits. For 8 bits, 28 = 256. The numbers 0 through 255 are the valid values. Another way of looking at it is that the lowest value would be 8 0’s or 00000000 (decimal 0). The highest value is 8 1’s or 11111111 (decimal 255).

5. For what purpose are IPv4 addresses utilized?

• An IPv4 address is used to uniquely identify a device on an IP network.
• An IPv4 address is burned into the network card to uniquely identify a device.
• An IPv4 address is used to uniquely identify the application that requested the information from a remote device.
• An IPv4 address is used to identify the number of IP networks available.

Explanation: A MAC address is burned into a NIC to uniquely identify a device. A port number is used to uniquely identify the application that requested information. The subnet mask identifies how many hosts can be on a network and the network number. There is not really any parameter that identifies the number of free IP networks.

6. What is the prefix length notation for the subnet mask 255.255.255.224?

• /25
• /26
• /27
• /28

Explanation: The binary format for 255.255.255.224 is 11111111.11111111.11111111.11100000. The prefix length is the number of consecutive 1s in the subnet mask. Therefore, the prefix length is /27.

7. Which two parts are components of an IPv4 address? (Choose two.)

• subnet portion
• network portion
• logical portion
• host portion
• physical portion

Explanation: An IPv4 address is divided into two parts: a network portion – to identify the specific network on which a host resides, and a host portion – to identify specific hosts on a network. A subnet mask is used to identify the length of each portion.

8. What is obtained when ANDing the address 192.168.65.3/18 with its subnet mask?

• 192.168.0.0
• 192.168.16.0
• 192.168.32.0
• 192.168.64.0

Explanation: The value of the IP address 192.168.65.3 in binary is 11000000.10101000.01001110.00000011. The value of the subnet mask in binary is 11111111.11111111.11000000.00000000. When ANDing the two, the result is 11000000.10101000.01000000.00000000, which in turn converts into 192.168.64.0.

9. What do devices on the same IPv4 subnet have in common?

• They all use the same default gateway.
• They all have a subnet mask of /8, /16, or /24.
• They all have the same last octet in their IPv4 addresses.
• They all have the same number in the first three octets of their IPv4 address.

Explanation: Devices on the same subnet will share the same network number, subnet mask, and default gateway. The default gateway is the IPv4 address of the Layer 3 device that allows the devices on the same subnet to communicate with other networks.

10. How many unique addresses are available for assignment to hosts in the network of 10.100.16.0 with subnet mask 255.255.252.0?

• 254
• 510
• 1022
• 4094

Explanation: To calculate how many unique addresses are available with a given network and subnet mask use the following formula:

2^n – 2 = number of addresses

where n = the number of low order bits representing host bits.

2^10 – 2 = 1022

11. Which is a valid default gateway address for a host configured with IP address 10.25.1.110 and a subnet mask of 255.255.255.192?

• 10.25.1.65
• 10.25.1.1
• 10.0.0.1
• 10.25.1.127

Explanation: To be valid, the default gateway address must be on the same subnet as the host. A host with an IP address 10.25.1.110 and a subnet mask of 255.255.255.192 is a member of the 10.25.1.64 subnet. This subnet has a usable host address range of 10.25.1.65 through 10.25.1.126. Any address within that range, with the exception of the address configured already on the host and the broadcast address of the subnet, is valid for a default gateway.

12. When IPv4 addressing is manually configured on a web server, which property of the IPv4 configuration identifies the network and host portion for an IPv4 address?

• default gateway

Explanation: There are several components that need to be entered when configuring IPv4 for an end device:

• IPv4 address – uniquely identifies an end device on the network