1. What does the IP address 172.17.4.250/24 represent?

Explanation: The /24 shows that the network address is 172.17.4.0. The broadcast address for this network would be 172.17.4.255. Useable host addresses for this network are 172.17.4.1 through 172.17.4.254.

2. If a network device has a mask of /28, how many IP addresses are available for hosts on this network?

• 256
• 254
• 62
• 32
• 16
• 14

Explanation: A /28 mask is the same as 255.255.255.240. This leaves 4 host bits. With 4 host bits, 16 IP addresses are possible, but one address represents the subnet number and one address represents the broadcast address. 14 addresses can then be used to assign to network devices.

3. What is the purpose of the subnet mask in conjunction with an IP address?

• to uniquely identify a host on a network
• to identify whether the address is public or private
• to determine the subnet to which the host belongs

Explanation: With the IPv4 address, a subnet mask is also necessary. A subnet mask is a special type of IPv4 address that coupled with the IP address determines the subnet of which the device is a member.

4. A network administrator is variably subnetting a network. The smallest subnet has a mask of 255.255.255.224. How many usable host addresses will this subnet provide?​

• 2
• 6
• 14
• 30
• 62

Explanation: The subnet mask 255.255.255.224 is equivalent to the /27 prefix. This leaves 5 bits for hosts, providing a total of 30 usable IP addresses (25 = 32 – 2 = 30).

5. What subnet mask is represented by the slash notation /20?

• 255.255.255.248
• 255.255.224.0
• 255.255.240.0
• 255.255.255.0
• 255.255.255.192

Explanation: The slash notation /20 represents a subnet mask with 20 1s. This would translate to: 11111111.11111111.11110000.0000, which in turn would convert into 255.255.240.0.

• Each subnet is the same size.
• The size of each subnet may be different, depending on requirements.
• Subnets may only be subnetted one additional time.
• Bits are returned, rather than borrowed, to create additional subnets.

Explanation: In variable-length subnet masking, bits are borrowed to create subnets. Additional bits may be borrowed to create additional subnets within the original subnets. This may continue until there are no bits available to borrow.

7. Why does a Layer 3 device perform the ANDing process on a destination IP address and subnet mask?

• to identify the host address of the destination host
• to identify faulty frames
• to identify the network address of the destination network

Explanation: ANDing allows us to identify the network address from the IP address and the network mask.

8. How many usable IP addresses are available on the 192.168.1.0/27 network?

• 256
• 254
• 62
• 30
• 16
• 32

Explanation: A /27 mask is the same as 255.255.255.224. This leaves 5 host bits. With 5 host bits, 32 IP addresses are possible, but one address represents the subnet number and one address represents the broadcast address. Thus, 30 addresses can then be used to assign to network devices.

9. Which subnet mask would be used if exactly 4 host bits are available?

• 255.255.255.224
• 255.255.255.128
• 255.255.255.240
• 255.255.255.248

Explanation: The subnet mask of 255.255.255.224 has 5 host bits. The mask of 255.255.255.128 results in 7 host bits. The mask of 255.255.255.240 has 4 host bits. Finally, 255.255.255.248 represents 3 host bits.

10. 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.

11. If a network device has a mask of /26, how many IP addresses are available for hosts on this network?

• 64
• 30
• 62
• 32
• 16
• 14

Explanation: A /26 mask is the same as 255.255.255.192. This leaves 6 host bits. With 6 host bits, 64 IP addresses are possible, but one address represents the subnet number and one address represents the broadcast address. Thus 62 addresses can then be assigned to network hosts.

12. 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.

13. How many valid host addresses are available on an IPv4 subnet that is configured with a /26 mask?

• 254
• 190
• 192
• 62
• 64

Explanation: When a /26 mask is used, 6 bits are used as host bits. With 6 bits, 64 addresses are possible, but one address is for the subnet number and one address is for a broadcast. This leaves 62 addresses that can be assigned to network devices.

14. Which subnet mask would be used if 5 host bits are available?

• 255.255.255.0
• 255.255.255.128
• 255.255.255.224
• 255.255.255.240

Explanation: The subnet mask of 255.255.255.0 has 8 host bits. The mask of 255.255.255.128 results in 7 host bits. The mask of 255.255.255.224 has 5 host bits. Finally, 255.255.255.240 represents 4 host bits.

15. A network administrator subnets the 192.168.10.0/24 network into subnets with /26 masks. How many equal-sized subnets are created?

• 1
• 2
• 4
• 8
• 16
• 64

Explanation: The normal mask for 192.168.10.0 is /24. A /26 mask indicates 2 bits have been borrowed for subnetting. With 2 bits, four subnets of equal size could be created.​