Subnetting Calculation

Subnetting Concept using FLSM

   Generally, subnetting is a process to divide a network into multiple small networks. Subnetting helps to maximize IP addressing efficiency by reducing the wastage of IP addresses. FLSM (Fixed Length Subnet Mask) is one of the types of network subnetting. In FLSM the length of each subnetworks is fixed. Based on the given case, class B address class is used as it is suitable for organizations with large networks likewise in the scenario. Class B network supports up to 65,536 hosts for each block whereby the network address ranges from 128.0.0.0 to 191.255.255.255. The suggested private IP address chosen for the OUM network is 149.76.0.0. OUM consists of 3 faculties and 1 IT center where the OnlineLearning System server is located. Every faculty and IT center has their own particular network address.

Steps for subnetting network using FLSM includes, first is finding the number of bits borrowed from host ID. Total number of subnet help to determine the number of bits borrowed by comparing it to the default mask of its class. The second step is finding the subnet mask which can be represented in binary or dotted decimal notation. For class B network, bit ‘1’s is added to the third byte of network address. Third step is find the number of hosts per subnet using the formula 2^x - 2 , where x is the number of 0 in the last two bytes of a class B network. Lastly find the valid subnet which is used to find the bounding between subnet. By using the information subnet mask, number of hosts per subnet and valid subnets, the network address, valid address range and broadcast address for all 3 faculties and IT Center can be determined. Since the IP address of OnlineLearning System is under the network address of IT Center, the IP address of OnlineLearning System will be located between the subnet for IT Center.

Subnetting Calculation

Address Class: Class B 

Network Address: 149.76.0.0 / 16

Default Subnet Mask: 255.255.0.0 

Subnet: 

(i) 3 Faculties 

(ii) IT Center (OnlineLearning System Server) 

Total Subnet = 4 

2^n = 4 

n = 2 (2 bits were borrowed where in binary is 11000000, 192 in decimal) 

Subnet Mask: 

Binary: 11111111 11111111 11000000 00000000 

Dotted-Decimal: 255.255.192.0 

Host per Subnet 

= 14 host bits off (11000000 00000000) 

= (2^14) - 2 (Except 2 for Network and Broadcast Address) 

= 16382 

Valid Subnets = 256-192 = 64 

(Subnetting is performed in the 3rd octet so subnet number is 0.0, 64.0, 128.0, 192.0)

Address of the OnlineLearning System Server 

= 4th available address 

= 149.76.192.4/18

Diagram shows a class B network is subnetted into 4 subnets by using FLSM.