Understanding Subnetting On Computer Networks

Understanding Subnetting On Computer Networks

NOTIVKU, Subnetting is the process of breaking up an IP network into smaller subnets called "subnets."Each subnet is a non-physical description (or ID) for a sub-physical network (typically a network switched from a host containing one router to a router in a multi-network).

Why subnetting? There are several reasons why we need to do subnetting, including the following:

• To streamline the allocation of IP addresses in a network in order to maximize the use of IP addresses.
• Overcoming the problem of differences in hardware and physical media used in a network, because an IP Router can only integrate various networks with different physical media if each network has a unique network address.
• Increase security and reduce congestion due to too many hosts in a network.

Subnetting calculations can be done in two ways, namely binary which is relatively slow and a special way that is faster. The default IP address is 192.168.1.2. But sometimes it is written with 192.168.1.2/24. The explanation is that the IP address is 192.168.1.2 with a subnet mask of 255.255.255.0. Why is it like that ?the /24 intent is taken from the calculation that the 24 bit subnet mask is shrouded with binary 1. Or in other words, the subnet mask is: 11111111.11111111.11111111.00000000 (255.255.255.0). This concept is called CIDR (Classless Inter-Domain Routing) which was first introduced in 1992 by IEFT. Essentially all questions about subnetting will revolve around four issues: number of subnets, number of Hosts per Subnet, Subnet blocks, and Host - Broadcast addresses.

1. Example of a Subnetting case that occurs with a NETWORK ADDRESS 10.0.0.0/16.

SUBNETTING OF CLASS A IP ADDRESSES

Class A in octets 2, 3 and 4 (last 3 octets). Then the subnet mask that can be used for Class A subnetting is all subnet masks from CIDR /8 to /30.

Analysis:

10.0.0.0 means Class A, with Subnet Mask /16 means 11111111.11111111.00000000.00000000 (255.255.0.0).

Counting:

Number of subnets = 28 = 256 subnets

Number of Hosts per Subnet = 216 – 2 = 65534 hosts

Subnet Block = 256 – 255 = 1. So the full subnet: 0,1,2,3,4, etc.

2. Examples of Subnetting cases that occur with a NETWORK address are 172.16.0.0/18 and 172.16.0.0/25.

 SUBNETTING PADA ALAMAT IP KELAS B

Based on the subnet block. CIDR /17 to /24 exactly the same way as subnetting Class C, only the subnet block we insert directly into the third octet, not like Class C is “played” in the fourth octet. While the CIDR /25 to /30 (multiples) of the subnet block we “play” in the fourth octet, but after completion of the third octet goes forward (coeunter) of 0, 1, 2, 3, etc.

> > Example network address 172.16.0.0/18

Analysis:

172.16.0.0 means Class B, with Subnet Mask /18 means 11111111.11111111.11000000.00000000 (255.255.192.0).

Counting:

Number of subnets = 2x, where x is the number of binary 1s in the last 2 octets. So the number of subnets is 22 = 4 subnets

Number of Hosts per Subnet = 2y-2, Where y is the inverse of x i.e. the number of binary 0s in the last 2 octets. So the number of hosts per subnet is 214 – 2 = 16,382 hosts

Subnet Block = 256 – 192 = 64. The next Subnet is 64 + 64 = 128, and 128+64=192. So the full subnet is 0, 64, 128, 192.

> > Example network address 172.16.0.0/25.

Analysis:

172.16.0.0 means Class B, with Subnet Mask /25 means 11111111.11111111.11111111.10000000 (255.255.255.128).

Counting:

Number of subnets = 29 = 512 subnets

Number of Hosts per Subnet = 27 – 2 = 126 hosts

Subnet Block = 256 – 128 = 128. So the complete is (0, 128)

3. Example of a Subnetting case that occurs with a NETWORK ADDRESS192. 168.1. 0/26

SUBNETTING OF CLASS C IP ADDRESSES

Also read: what is a VLAN ? how to create a VLAN

Analysis :

192.168.1.0 means Class C with Subnet Mask /26 means 11111111.11111111.11111111.11000000 (255.255.255.192).

Counting :

Number of subnets = 2x, where x is the number of binaries 1 in the last octet of the subnet mask (the last 2 octets for Class B, and the last 3 octets for Class A). So the number of subnets is 22 = 4 subnets

Number of Hosts per Subnet = 2y – 2, Where y is the inverse of x which is the number of binary 0s in the last octet of the subnet. So the number of hosts per subnet is 26 – 2 = 62 hosts

Subnet block = 256 – 192 (value of the last octet of the subnet mask) = 64. The next Subnet is 64 + 64 = 128, and 128+64=192. So the full subnet is 0, 64, 128, 192.