IPv4 Subnetting: A Quick Overview
The practice of dividing a network into two or more networks is called subnetting. We steal bits from the hosts to create more subnets.
Public IP range – Used with the public network ex. WAN; Recognized over the internet, assigned by IANA or service provider. globally unique, cost associated with public IP.
CLASS | IP Address Range | Network Mask | Prefix | Number of Networks | Number of hosts |
A | 1 to 126 – Used for huge networks, like those deployed by Internet Service Providers (ISPs). | 255.0.0.0 | /8 | 125 | 16,777,241 |
B | 128 to 191 – Used for medium and large-sized networks in enterprises and organizations | 255.255.0.0 | /16 | 16,382 | 65,534 |
C | 192 to 223 – Used for small-sized networks. | 255.255.255.0 | /24 | 2,097,150 | 254 |
D | 224 to 239 – Used for multicasting applications | Multicast Addresses | |||
E | 240 to 254 – Reserved for experimental purposes only for R&D or Study. | R&D, Restricted/Experimental | |||
The above table is standard and good to remember but the actual range will look like below after excluding private IP range.
CLASS A | 1.0.0.0 – 9.255.255.255 11.0.0.0 – 126.255.255.255 |
CLASS B | 128.0.0.0 – 172.15.255.255 172.32.0.0 – 191.255.255.255 |
CLASS C | 192.0.0.0 – 192.167.255.255 192.169.0.0 – 223.255.255.255 |
127.0.0.0 is reserved for loopback (localhost).
Private IP range – Used with the private network ex. LAN; Not recognized over the internet, assigned by LAN Admin. unique only in LAN segment. free of charge.
CLASS A | 10.0.0.0 – 10.255.255.255 – Used for private network, local LAN. |
CLASS B | 172.16.0.0 – 172.31.255.255 – Used for private network, local LAN. |
CLASS C | 192.168.0.0 – 192.168.255.255 – Used for private network, local LAN. |
Types of Subnetting
- Fixed Length Subnetting – All the subnets are of same size, same subnet mask, equal number of hosts. It is also called as classful subnetting.
- Variable Length Subnetting – All the subnets are not of same size, do not have same subnet mask, no equal number of hosts. It is also called as classless subnetting
Types of addresses
- Network address – Network address represents the network.
- Broadcast address – Broadcast address represents all the hosts which belong to it.
Subnetting Table (Class A) –
NetBits | Network Mask | Subnets | Number of Hosts |
/8 | 255.0.0.0 | 0 | 16,777,214 |
/9 | 255.128.0.0 | 0 | 8,388,606 |
/10 | 255.192.0.0 | 2 | 4,194,302 |
/11 | 255.224.0.0 | 6 | 2,097,150 |
/12 | 255.240.0.0 | 14 | 1,048,574 |
/13 | 255.248.0.0 | 30 | 524,286 |
/14 | 255.252.0.0 | 62 | 262,142 |
/15 | 255.254.0.0 | 126 | 131,070 |
/16 | 255.255.0.0 | 254 | 65,534 |
/17 | 255.255.128.0 | 510 | 32,766 |
/18 | 255.255.192.0 | 1,022 | 16,382 |
/19 | 255.255.224.0 | 2,046 | 8,190 |
/20 | 255.255.240.0 | 4,094 | 4,094 |
/21 | 255.255.248.0 | 8,190 | 2,046 |
/22 | 255.255.252.0 | 16,382 | 1,022 |
/23 | 255.255.254.0 | 32,766 | 510 |
/24 | 255.255.255.0 | 65,534 | 254 |
/25 | 255.255.255.128 | 131,070 | 126 |
/26 | 255.255.255.192 | 262,142 | 62 |
/27 | 255.255.255.224 | 524,286 | 30 |
/28 | 255.255.255.240 | 1,048,574 | 14 |
/29 | 255.255.255.248 | 2,097,150 | 6 |
/30 | 255.255.255.252 | 4,194,302 | 2 |
Subnetting Table (Class B) –
NetBits | Network Mask | Subnets | Number of Hosts |
/16 | 255.255.0.0 | 0 | 65,534 |
/17 | 255.255.128.0 | 0 | 32,766 |
/18 | 255.255.192.0 | 2 | 16,382 |
/19 | 255.255.224.0 | 6 | 8,190 |
/20 | 255.255.240.0 | 14 | 4,094 |
/21 | 255.255.248.0 | 30 | 2,046 |
/22 | 255.255.252.0 | 62 | 1,022 |
/23 | 255.255.254.0 | 126 | 510 |
/24 | 255.255.255.0 | 254 | 254 |
/25 | 255.255.255.128 | 510 | 126 |
/26 | 255.255.255.192 | 1,022 | 62 |
/27 | 255.255.255.224 | 2,046 | 30 |
/28 | 255.255.255.240 | 4,094 | 14 |
/29 | 255.255.255.248 | 8,190 | 6 |
/30 | 255.255.255.252 | 16,382 | 2 |
Subnetting Table (Class C) –
NetBits | Network Mask | Subnets | Number of Hosts |
/24 | 255.255.255.0 | 0 | 254 |
/25 | 255.255.255.128 | 0 | 126 |
/26 | 255.255.255.192 | 2 | 62 |
/27 | 255.255.255.224 | 6 | 30 |
/28 | 255.255.255.240 | 14 | 14 |
/29 | 255.255.255.248 | 30 | 6 |
/30 | 255.255.255.252 | 62 | 2 |