Subnetting using binary method.

Alexandr Satalov

Hello everyone. I'm trying to prepare to Network+ exam watching a Net+ course right now.
As I can see you guys using this binary method to calculate Network ID, Broadcast address, first\last IP etc.
I watched all your examples with class C IP addresses.
Could you help me with class B? I'm not sure how to act when I subnetting B or A classes.
For instance I'm looking at an example:
Find the subnet ID (network ID I presume)
IP address : 165.245.77.14
Subnet mask : 255.255.240.0
I'm able to convert this into binary :
165.245.01001101.00001110
255.255.11110000.00000000
I assume we have default allocation which is /16 and after this I'm confused not sure what to do next,
Thank you for your help in advance.

P.s. a quick feedback would be nice if you add A or B example to your course. Thanks a lot.

Ronnie Wong

@Alexandr-Satalov,

For instance I'm looking at an example:
Find the subnet ID (network ID I presume)
IP address : 165.245.77.14
Subnet mask : 255.255.240.0
I'm able to convert this into binary :
165.245.01001101.00001110
255.255.11110000.00000000
I assume we have default allocation which is /16 and after this I'm confused not sure what to do next,
Thank you for your help in advance.

With this given information, you're trying to determine which class B subnet that the IP address belongs. I will begin the process so you can see if you can determine which one.

So a class B begins with 16 bit subnet mask. You've added an additional 4 bits to it from the HOST bits. These 4 bits now becomes your network IDs.

1st network

165.245.0000|0000.00001110 = 165.245.0.0
255.255.1111|0000.00000000 = 255.255.240.0

2nd network
165.245.0001|0000.00001110 = 165.245.16.0
255.255.1111|0000.00000000

3rd network
165.245.0010|0000.00001110 = 165.245.32.0
255.255.1111|0000.00000000

4th network
165.245.0011|0000.00001110 = 165.245.48.0
255.255.1111|0000.00000000

5th network
165.245.0100|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

6th network
165.245.0101|000000001110 = 165.245.___.0
255.255.1111|0000.00000000

7th network
165.245.0110|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

8th network
165.245.0111|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

9th network
165.245.1000|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

10th network
165.245.1001|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

11th network
165.245.1010|0000.00001110 = 165.245.____.0
255.255.1111|0000.00000000

12th network
165.245.1011|0000.00001110 = 165.245.___.0
255.255.1111|0000.00000000

13th network
165.245.1100|0000.00001110 = 165.245.XXX.0
255.255.1111|0000.00000000

14th network
165.245.1101|0000.00001110 = 165.245.XXX.0
255.255.1111|0000.00000000

15th network
165.245.1110|0000.00001110 = 165.245.XXX.0
255.255.1111|0000.00000000

16th network
165.245.1111|0000.00001110 = 165.245.XXX.0
255.255.1111|0000.00000000

Examples of Class A and Class B, you may want to look into the Cisco CCNA show there is an example there. At the Network+ level, we're really introducing you to the concept and we must start and stay with Class C.