SUBNETTING CALCULATION

The scenario of this project can be referred to Figure 1. Figure 1 shows the logical network flow from a home network to UTeM facilities. In this figure, a UTeM’s student is trying to access the Ulearn system located in the UTeM network facilities. The student is using her modem to connect to the public network before able to connect to the UTeM facilities. From the UTeM network, the data then was forwarded to IT Center where the Ulearn System server is located.

Figure 1: Logical Network Flow

Students are required to suggest private addressing scheme used in UTeM network. Explain how you calculate the subnetting using FLSM based on the number of the faculties. The number of students of each faculty is within 500 – 1000 students. Each faculty is given their network address. Assign IT Center as another subnet with their own network address. From this network address, assigned as the 5^th available address as the address of the Ulearn System Server. 

Private IP addresses are

• Non-routable addresses - Routers would not deliver packets with private IP addresses
• Free to use without anyone's permission

Why do we need private IP addresses

• There are only 4.3 billion IPv4 addresses
• Private IP address is used to communicate within the network
• They have extended IPv4's life

                                  IPv4 Private Addresses

Class	Range
A	10.0.0.0 – 10.255.255.255 or 10.0.0.0/8
B	172.16.0.0 – 172.31.255.255 or 172.16.0.0/12
C	192.168.0.0 – 192.168.255.255 or 192.168.0.0/16

                                                   Table 1

A fixed-length mask(FLSM) refers to a type of enterprise or provider networking where a block of IP addresses is divided into multiple subnets of equal length. FLSM streamlines packet routing within the subnets of a proprietary network.

A subnet can be a geographically defined local area network (LAN). Alternatively, it may define security boundaries, departmental boundaries, multicast zones or hardware security parameters. One benefit is to create locally significant subnet identification addresses.

Subnetting

• divides a network into two or more networks
• takes bits from the host portion of the IP address and reserve them to define the subnet address

In short, Subnetting is the process of stealing bits from the HOST part of an IP address in order to divide the larger network into smaller sub-networks called subnets. After subnetting, we end up with NETWORK SUBNET HOST fields. We always reserve an IP address to identify the subnet and another one to identify the broadcast subnet address.

Subnetting means dividing a network into multiple smaller subnetworks by using a subnetting mask. In FLSM, the number of IP addresses is the same in each subnet. Another way of saying this is that the same number of IP addresses are allocated to each subnet. Therefore, the subnet mask used will be the same for all the subnets.

For UTeM network,

To do the subnetting calculation, below shows the five-step subnetting process.

STEP 1: Suggest a private addressing scheme

Referring to Table 1, 

192.168.0.0 /16 (Class C)

Subnet Mask - 255.255.0.0

STEP 2: Find the number of required subnets

The number of required subnets is 2. One subnet is for the use of faculties and the other subnet is for the use of IT centre.

Figure 2

STEP 3A: Determine number of bits to borrow

By referring to Figure 2, since the number of required bits is 2, the number of bits to borrow is 2.

STEP 3B: Determine Number of Hosts per Subnet

By referring to Figure 2, since the number of required bits is 2, the number of hosts per subnet is 126.

However, the borrowed bits is at third field, so the actual number of hosts per subnet is calculated by 2^14 - 2 = 16382

Prefix size	Network mask	Usable hosts per subnet
/1	128.0.0.0	2,147,483,646
/2	192.0.0.0	1,073,741,822
/3	224.0.0.0	536,870,910
/4	240.0.0.0	268,435,454
/5	248.0.0.0	134,217,726
/6	252.0.0.0	67,108,862
/7	254.0.0.0	33,554,430
Class A
/8	255.0.0.0	16,777,214
/9	255.128.0.0	8,388,606
/10	255.192.0.0	4,194,302
/11	255.224.0.0	2,097,150
/12	255.240.0.0	1,048,574
/13	255.248.0.0	524,286
/14	255.252.0.0	262,142
/15	255.254.0.0	131,070
Class B
/16	255.255.0.0	65,534
/17	255.255.128.0	32,766
/18	255.255.192.0	16,382
/19	255.255.224.0	8,190
/20	255.255.240.0	4,094
/21	255.255.248.0	2,046
/22	255.255.252.0	1,022
/23	255.255.254.0	510
Class C
/24	255.255.255.0	254
/25	255.255.255.128	126
/26	255.255.255.192	62
/27	255.255.255.224	30
/28	255.255.255.240	14
/29	255.255.255.248	6
/30	255.255.255.252	2
/31	255.255.255.254	0
/32	255.255.255.255	0

Figure 3

STEP 4: Calculate new subnet mask and prefix

By referring to Figure 3, since the number of usable hosts is 16382, 

New Subnet Mask = 255.255.192.0

New Prefix = /18

STEP 5: Apply the subnet mask to the IP space

Usage	Subnet ID	Usable Range	Broadcast ID
Faculties	192.168.0.0 /18	192.168.0.1 /18  – 192.168.127.254 /18	192.168.127.255 /18
IT Centre	192.168.128.0 /18	192.168.128.1 /18  – 192.168.255.254 /18	192.168.255.255 /18

                                                              Table 2

The address of Ulearn System Server is located in the  5^th available address of IT Centre. By referring to Table 2, the 5^th available address is 192.168.128.6. We do not start from 192.168.128.1 because it will set up as router IP Address for that subnet and become default gateway. So, it should start from 192.168.128.2 and so on. The scenario said that the Ulearn System Server is assigned as the 5th available address and make 192.168.128.6 as their assigned IP address.