IPv4 Subnetting (Class A, Class B and Class C)

Each IP class is supplied with its own default subnet mask that bounds that IP class to own prefixed variety of Networks and prefixed number of Hosts per network. classful IP addressing doesn’t give any flexibility of getting less number of Hosts per Network or a lot of Networks per IP Class.

CIDR or Classless Inter Domain Routing provides the pliability of borrowing bits of Host a part of the IP address and victimisation them as Network in Network, referred to as Subnet. By victimisation subnetting, one single class A IP address will be used to have smaller sub-networks that provides higher network management capabilities.

IPv4 Class A Subnets

In Class A, solely the first octet is used as Network symbol and remainder of 3 octets are used to be assigned to Hosts (i.e. 16777214 Hosts per Network). to create a lot of subnet in class A, bits from Host part are borrowed and therefore the subnet mask is modified consequently.

For example, if one MSB (Most Significant Bit) is borrowed from host bits of second octet and added to Network address, it creates 2 Subnets (21=2) with (223-2) 8388606 Hosts per Subnet.

The Subnet mask is modified consequently to mirror subnetting. Given below may be a list of all potential combination of class A subnets:

Network Bits Subnet Mask Bits Borrowed Subnets Hosts/Subnet
8 255.0.0.0 0 1 16777214
9 255.128.0.0 1 2 8388606
10 255.192.0.0 2 4 4194302
11 255.224.0.0 3 8 2097150
12 255.240.0.0 4 16 1048574
13 255.248.0.0 5 32 524286
14 255.252.0.0 6 64 262142
15 255.254.0.0 7 128 131070
16 255.255.0.0 8 256 65534
17 255.255.128.0 9 512 32766
18 255.255.192.0 10 1024 16382
19 255.255.224.0 11 2048 8190
20 255.255.240.0 12 4096 4094
21 255.255.248.0 13 8192 2046
22 255.255.252.0 14 16384 1022
23 255.255.254.0 15 32768 510
24 255.255.255.0 16 65536 254
25 255.255.255.128 17 131072 126
26 255.255.255.192 18 262144 62
27 255.255.255.224 19 524288 30
28 255.255.255.240 20 1048576 14
29 255.255.255.248 21 2097152 6
30 255.255.255.252 22 4194304 2

In case of subnetting too, the terribly first and last IP address of each subnet is used for Subnet number and Subnet Broadcast IP address severally. as a result of these 2 IP addresses can’t be assigned to hosts, sub-netting can’t be enforced by using quite 30 bits as Network Bits, that provides only 2 hosts per subnet.

IPv4 Class B Subnets

By default, using Classful Networking, fourteen bits are used as Network bits providing (214)  16384 Networks and (216-1) 65534 Hosts. class B IP Addresses will be subnetted constant means as class A addresses, by borrowing bits from Host bits. Below is given all potential combination of class B subnetting:

Network Bits Subnet Mask Bits Borrowed Subnets Hosts/Subnet
16 255.255.0.0 0 1 65534
17 255.255.128.0 1 2 32766
18 255.255.192.0 2 4 16382
19 255.255.224.0 3 8 8190
20 255.255.240.0 4 16 4094
21 255.255.248.0 5 32 2046
22 255.255.252.0 6 64 1022
23 255.255.254.0 7 128 510
24 255.255.255.0 8 256 254
25 255.255.255.128 9 512 126
26 255.255.255.192 10 1024 62
27 255.255.255.224 11 2048 30
28 255.255.255.240 12 4096 14
29 255.255.255.248 13 8192 6
30 255.255.255.252 14 16384 2


IPv4 
Class C Subnets

Class C IP addresses are ordinarily assigned to a really little size network as a result of it will only have 254 hosts per network. Given below may be a list of all potential combination of subnetted class B IP address:

Class C ip addresses are usually allotted to small size network as a result of it will solely have 254 hosts in an exceedingly network. Given below could be a list of all potential combination of subnetted class B ip address:

Network Bits Subnet Mask Bits Borrowed Subnets Hosts/Subnet
24 255.255.255.0 0 1 254
25 255.255.255.128 1 2 126
26 255.255.255.192 2 4 62
27 255.255.255.224 3 8 30
28 255.255.255.240 4 16 14
29 255.255.255.248 5 32 6
30 255.255.255.252 6 64 2

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