Subnetting problems
- 1. Which two statements describe the IP address 10.16.3.65/23?
- The subnet address is 10.16.3.0 255.255.254.0.
- The lowest host address in the subnet is 10.16.2.1 255.255.254.0.
- The last valid host address in the subnet is 10.16.2.254 255.255.254.0.
- The broadcast address of the subnet is 10.16.3.255 255.255.254.0.
Options- A. 1 and 3
- B. 2 and 4
- C. 1, 2 and 4
- D. 2, 3 and 4 Discuss
Correct Answer: 2 and 4
Explanation:
The mask 255.255.254.0 (/23) used with a Class A address means that there are 15 subnet bits and 9 host bits. The block size in the third octet is 2 (256 - 254). So this makes the subnets in the interesting octet 0, 2, 4, 6, etc., all the way to 254. The host 10.16.3.65 is in the 2.0 subnet. The next subnet is 4.0, so the broadcast address for the 2.0 subnet is 3.255. The valid host addresses are 2.1 through 3.254.
- 2. Using the following illustration, what would be the IP address of E0 if you were using the eighth subnet? The network ID is 192.168.10.0/28 and you need to use the last available IP address in the range. The zero subnet should not be considered valid for this question.
Options- A. 192.168.10.142
- B. 192.168.10.66
- C. 192.168.100.254
- D. 192.168.10.143
- E. 192.168.10.126 Discuss
Correct Answer: 192.168.10.142
Explanation:
A /28 is a 255.255.255.240 mask. Let's count to the ninth subnet (we need to find the broadcast address of the eighth subnet, so we need to count to the ninth subnet). Starting at 16 (remember, the question stated that we will not use subnet zero, so we start at 16, not 0), 16, 32, 48, 64, 80, 96, 112, 128, 144. The eighth subnet is 128 and the next subnet is 144, so our broadcast address of the 128 subnet is 143. This makes the host range 129-142. 142 is the last valid host.
- 3. The network address of 172.16.0.0/19 provides how many subnets and hosts?
Options- A. 7 subnets, 30 hosts each
- B. 8 subnets, 8,190 hosts each
- C. 8 subnets, 2,046 hosts each
- D. 7 subnets, 2,046 hosts each Discuss
Correct Answer: 8 subnets, 8,190 hosts each
Explanation:
A CIDR address of /19 is 255.255.224.0. This is a Class B address, so that is only 3 subnet bits, but it provides 13 host bits, or 8 subnets, each with 8,190 hosts.
- 4. Your router has the following IP address on Ethernet0: 172.16.2.1/23. Which of the following can be valid host IDs on the LAN interface attached to the router?
- 172.16.1.100
- 172.16.1.198
- 172.16.2.255
- 172.16.3.0
Options- A. 1 only
- B. 2 and 3 only
- C. 3 and 4 only
- D. None of the above Discuss
Correct Answer: 3 and 4 only
Explanation:
The router's IP address on the E0 interface is 172.16.2.1/23, which is 255.255.254.0. This makes the third octet a block size of 2. The router's interface is in the 2.0 subnet, and the broadcast address is 3.255 because the next subnet is 4.0. The valid host range is 2.1 through 3.254. The router is using the first valid host address in the range.
- 5. You have an interface on a router with the IP address of 192.168.192.10/29. Including the router interface, how many hosts can have IP addresses on the LAN attached to the router interface?
Options- A. 6
- B. 8
- C. 30
- D. 32 Discuss
Correct Answer: 6
Explanation:
A /29 (255.255.255.248), regardless of the class of address, has only 3 host bits. Six hosts is the maximum number of hosts on this LAN, including the router interface.
- 6. To test the IP stack on your local host, which IP address would you ping?
Options- A. 127.0.0.0
- B. 1.0.0.127
- C. 127.0.0.1
- D. 127.0.0.255 Discuss
Correct Answer: 127.0.0.1
Explanation:
To test the local stack on your host, ping the loopback interface of 127.0.0.1.
- 7. What is the subnetwork address for a host with the IP address 200.10.5.68/28?
Options- A. 200.10.5.56
- B. 200.10.5.32
- C. 200.10.5.64
- D. 200.10.5.0 Discuss
Correct Answer: 200.10.5.64
Explanation:
This is a pretty simple question. A /28 is 255.255.255.240, which means that our block size is 16 in the fourth octet. 0, 16, 32, 48, 64, 80, etc. The host is in the 64 subnet.
- 8. What is the maximum number of IP addresses that can be assigned to hosts on a local subnet that uses the 255.255.255.224 subnet mask?
Options- A. 14
- B. 15
- C. 16
- D. 30 Discuss
Correct Answer: 30
Explanation:
A /27 (255.255.255.224) is 3 bits on and 5 bits off. This provides 8 subnets, each with 30 hosts. Does it matter if this mask is used with a Class A, B, or C network address? Not at all. The number of host bits would never change.
- 9. You need to subnet a network that has 5 subnets, each with at least 16 hosts. Which classful subnet mask would you use?
Options- A. 255.255.255.192
- B. 255.255.255.224
- C. 255.255.255.240
- D. 255.255.255.248 Discuss
Correct Answer: 255.255.255.224
Explanation:
You need 5 subnets, each with at least 16 hosts. The mask 255.255.255.240 provides 16 subnets with 14 hosts-this will not work. The mask 255.255.255.224 provides 8 subnets, each with 30 hosts. This is the best answer.
- 10. Which configuration command must be in effect to allow the use of 8 subnets if the Class C subnet mask is 255.255.255.224?
Options- A. Router(config)#ip classless
- B. Router(config)#no ip classful
- C. Router(config)#ip unnumbered
- D. Router(config)#ip subnet-zero Discuss
Correct Answer: Router(config)#ip subnet-zero
Explanation:
A Class C subnet mask of 255.255.255.224 is 3 bits on and 5 bits off (11100000) and provides 8 subnets, each with 30 hosts. However, if the command
ip subnet-zero is not used, then only 6 subnets would be available for use.
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