Subnet Mask

Problem:

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?

1) 172.16.1.100

2) 172.16.1.198

3) 172.16.2.255

4) 172.16.3.0

A. 1 only

B. 2 and 3 only

C. 3 and 4 only

D. None of the above

Answer : C

Explanation:

172 Binary number  =10101100

16 Binary number    =00010000

2 Binary number      =00000010

1 Binary number      =00000001

Given IP172.16.2.1=10101100.00010000.00000010.00000001

Subnet mask /23   =11111111.11111111.11111110.00000000

AND Operation

Network Address  =10101100.00010000.00000010.00000000

Network Address     =172.16.2.0      (NID=1 HID=0)

Broad cast Address =172.16.3.255  (NID=1 HID=1)

Valid First Host Id = 172.16.2.1    (Add +1 to Network Address)

Valid Last Host Id = 172.16.3.254 (subtract  -1 to Broad cast Address)

Problem

Which two statements describe the IP address 10.16.3.65/23?

1)The subnet address is 10.16.3.0     255.255.254.0.

2)The lowest host address in the subnet is 10.16.2.1   255.255.254.0.

3)The last valid host address in the subnet is 10.16.2.254 255.255.254.0.

4)The broadcast address of the subnet is 10.16.3.255  255.255.254.0.

A. 1 and 3

B. 2 and 4

C. 1, 2 and 4

D. 2, 3 and 4

Answer:B

Explanation:

10 Binary number     =00001010

16 Binary number     =00010000

3  Binary number      =00000011

65 Binary number     =01000001

Given IP 10.16.3.65 =00001010.00010000.00000011.01000001

Subnet mask /23     =11111111.11111111.11111110.00000000

AND Operation          --------------------------------------- **********

Network Address    =00001010.00010000.00000010.00000000

Network Address     =10.16.2.0      (-NID=1 *HID=0)

Broad cast Address =10.16.3.255  (-NID=1 *HID=1)

Valid First Host Id = 10.16.2.1    (Add +1 to Network Address)

Valid Last Host Id = 10.16.3.254 (subtract  -1 to Broad cast Address)

Problem

Which subnet does host 172.27.25.187/23 belong to?

Answer: subnet Network Address is   =172.27.24.0 

Explanation:

172 Binary number   =10101100

27 Binary number     =00011011

25 Binary number     =00011001

187 Binary number   =10111011

Given IP172.27.25.187=10101100.00011011.00011001.10111011

Subnet mask /23          =11111111.11111111.11111110.00000000

AND Operation                --------------------------------------**********

Network Address         =10101100.00011011.00011000.00000000

Network Address     =172.27.24.0      (-NID=1 *HID=0)

Broad cast Address =172.27.25.255  (-NID=1 *HID=1)

Valid First Host Id      = 172.27.24.1    (Add +1 to Network Address)

Valid Last Host Id =172.27.25.254 (subtract  -1 to Broad cast Address)

Problem:

How many subnets and hosts per subnet can you get from the network 172.28.0.0 255.255.254.0?

Explanation:

172 Binary number   =10101100

28 Binary number     =00011100

0 Binary number       =00000000

0 Binary number       =00000000

255 Binary number   =11111111

254 Binary number   =11111110

Given IP

172.28.0.0       

10101100.00011100.00000000.00000000

Subnet mask

255.255.254.0

11111111.11111111.11111110.00000000

---------------------------------------**********

AND Operation

Network Address

10101100.00011100.00000000.00000000

To find the subnets we need to observe the number of 1's placed in 3 rd octet because there is a change observed in the given subnet mask i.e  2 power 7 = 128 subnets

To find the hosts per subnet we need to observe the number of 0's placed from 3 rd octet to 4th octet i.e  2 power 9 = 512 -2 =510 Host 

Problem:

How many subnets and hosts per subnet can you get from the network 172.21.0.0/28?

Explanation:

172 Binary number   =10101100

21 Binary number     =00010101

0 Binary number       =00000000

0 Binary number       =00000000

255 Binary number   =11111111

Given IP

172.21.0.0       

10101100.00010101.00000000.00000000

Subnet mask /28

11111111.11111111.11111111.11110000

------------------------------------------------ ****

AND Operation

Network Address

10101100.00010101.00000000.00000000

To find the subnets we need to observe the number of 1's placed in 3 rd & 4th octet because there is a change observed in the given subnet mask i.e  2 power 12 = 4096 subnets

To find the hosts per subnet we need to observe the number of 0's placed from 4th octet i.e  2 power 4 = 16 -2 =14 Host

 

You are designing a subnet mask for the 172.29.0.0 network. You want 60 subnets with up to 600 hosts on each subnet. What subnet mask should you use?