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?

Introduction to Networking

 

IP sharing: Your ISP assigns you one IP address. If you have a desktop, a laptop, a media box on your TV, and an iPad, that one IP address clearly isn’t going to cut it. A router manages those multiple connections and ensures that the right packets of information go to the right places. Without this function, there would be no way for a person on the desktop and a person on the laptop to both browse the web as there would be no distinguishing between which computer was requesting what.

Network Address Translation (NAT): Related to the IP sharing function, NAT modifies the headers in packets of information coming into and out of your network so that they get routed to the proper device. Think of NAT like a very helpful receptionist inside your router that knows exactly where every incoming/outgoing package should go and stamps the department on them accordingly.

Dynamic Host Configuration: Without DHCP you would have to manually configure and add all the hosts to your network. This means every time a new computer entered the network you would have to manually assign it an address on the network. DHCP does that for you automatically so that when you plug your XBOX into your router, your friend gets on your wireless network, or you add a new computer, an address is assigned with no human interaction required.

Firewall: Routers act as basic firewalls in a variety of ways including automatically rejecting incoming data that is not part of an ongoing exchange between a computer within your network and the outside world. If you request a music stream from Pandora, for example, your router says, “We’re expecting you, come on in” and that stream of data is directed to the device that made the request. On the other hand, if a sudden burst of port probing comes in from an unknown address your router acts as a bouncer and rejects the requests, effectively cloaking your computers. Even for a user with a single computer a simple $50 router is worth it for the firewall functionality alone.