Question

Your corporation was assigned a Class B IP address and has 7 very large departments. Each department needs their own subnet. (Block size is 64)

Create the configuration!

	Your turn to fill it in!
Class B IP address	172.17.0.0
Item 21 Class B Default Mask in Binary
Item 22 Default Mask in Decimal
Item 23 New Subnet Mask in Binary
Item 24 New Subnet Mask CIDR
Item 25 Highlight right-most 1 in Binary Mask
Item 26 Block Size
Item 27New Subnet Mask in Decimal
Item 28 Number of subnets
Item 29 Number of possible hosts in each subnet

Answer 1

I will start from the block size. Block size given is 64.

It means we need 6 bits for hosts. Remaining bits will become part of network id, i.e. 26 (32-6) bits for network part and 6 bits for hosts part. Hence, CIDR will be /26. No of subnets = 2¹⁰ (Class B CIDR is /16 and we will use /26. So 26-16 = 10) . Although we sill use only 7 subnets, but there are subnets available which can be used in future.

	Your turn to fill it in!
Class B IP address	172.17.0.0
Item 21 Class B Default Mask in Binary	11111111.11111111.00000000.00000000
Item 22 Default Mask in Decimal	255.255.0.0
Item 23 New Subnet Mask in Binary	11111111.11111111.11111111.11000000
Item 24 New Subnet Mask CIDR	/26
Item 25 Highlight right-most 1 in Binary Mask	11111111.11111111.11111111.1 1 000000
Item 26 Block Size	64
Item 27New Subnet Mask in Decimal	255.255.255.192
Item 28 Number of subnets	210 = 1024
Item 29 Number of possible hosts in each subnet	64-2 = 62.Block size is 64.One IP is reserved for network id and one IP for Broadcast. Henc, -2.

If we start from no of subnets then the answer will be as follows.

It means we need 3 bits for subnets.Hence, total number of subnets will be 2³ = 8. No of bits left for host = 32 - 16 - 3 = 13. Old CIDR is /16. New CIDR will be /19. No of host per subnet will be 2¹³.

	Your turn to fill it in!
Class B IP address	172.17.0.0
Item 21 Class B Default Mask in Binary	11111111.11111111.00000000.00000000
Item 22 Default Mask in Decimal	255.255.0.0
Item 23 New Subnet Mask in Binary	11111111.11111111.11100000.00000000
Item 24 New Subnet Mask CIDR	/19
Item 25 Highlight right-most 1 in Binary Mask	11111111.11111111.11 1 00000.00000000
Item 26 Block Size	213
Item 27New Subnet Mask in Decimal	255.255.224.0
Item 28 Number of subnets	23 = 8
Item 29 Number of possible hosts in each subnet	213 -2. One IP is reserved for network id and one IP for Broadcast. Henc, -2.