| IP Subnetting |
Updated IP Subnetting Info @ randomKaos
These are tables to help in the understanding and generation of VLSM (Variable Length Subnet Masks) networks and CIDR (Classless Inter Domain Routing) which is what the Internet currently uses to route packets on the Internet Backbone. It makes it possible to represent the millions of networks which form the Internet to be represented by less than 100,000 routes.
Although years ago we couldn't use the "Zero Subnet" now we can, current IP stacks support using this address space. Same devices may have to be configured Cisco routers for example need the command "ip subnet-zero" put in and while you are at it do "ip classless".
Network Address Ranges by Class
Top
Network Address Ranges by Class
IP network addresses are issued as follows:
| Class | Range | Default Mask |
| Class A | 1-127 | 255.0.0.0 |
| Class B | 128-191 | 255.255.0.0 |
| Class C | 192-223 | 255.255.255.0 |
Top
Maximum Number of Hosts by Class
| Class | No. of Addresses | |
| Class A | 2^24 | 16,777,216 |
| Class B | 2^16 | 65,536 |
| Class C | 2^8 | 256 |
Top
Binary Calculations
| 2^0 | 1 | 00000001 |
| 2^1 | 2 | 00000010 |
| 2^2 | 4 | 00000100 |
| 2^3 | 8 | 00001000 |
| 2^4 | 16 | 00010000 |
| 2^5 | 32 | 00100000 |
| 2^6 | 64 | 01000000 |
| 2^7 | 128 | 10000000 |
Top
Subnet Masks - Binary Representations
| Decimal | Binary | |
| .192 | 11000000 | 2 bits |
| .224 | 11100000 | 3 bits |
| .240 | 11110000 | 4 bits |
| .248 | 11111000 | 5 bits |
| .252 | 11111100 | 6 bits |
| .254 | 11111110 | 7 bits |
| .255 | 11111111 | 8 bits |
Top
CIDR (Classless Inter Domain Routing) Bits to Mask
This tale helps with notation 192.168.4.4/30
| # Bits | Subnet Mask |
| 8 | 255.0.0.0 |
| 16 | 255.255.0.0 |
| 17 | 255.255.128.0 |
| 18 | 255.255.192.0 |
| 19 | 255.255.224.0 |
| 20 | 255.255.240.0 |
| 21 | 255.255.248.0 |
| 22 | 255.255.252.0 |
| 23 | 255.255.254.0 |
| 24 | 255.255.255.0 |
| 25 | 255.255.255.128 |
| 26 | 255.255.255.192 |
| 27 | 255.255.255.224 |
| 28 | 255.255.255.240 |
| 29 | 255.255.255.248 |
| 30 | 255.255.255.252 |
| 31 | 255.255.255.254 |
| 32 | 255.255.255.255 |
Top
Classfull Subnetting Tables
| Class B | |||
| # of bits | Subnet Mask | # Subnets | # Hosts |
| 2 | 255.255.192.0 | 2 | 16382 |
| 3 | 255.255.224.0 | 6 | 8190 |
| 4 | 255.255.240.0 | 14 | 4094 |
| 5 | 255.255.248.0 | 30 | 2046 |
| 6 | 255.255.252.0 | 62 | 1022 |
| 7 | 255.255.254.0 | 126 | 510 |
| 8 | 255.255.255.0 | 254 | 254 |
| 9 | 255.255.255.128 | 510 | 126 |
| 10 | 255.255.255.192 | 1022 | 62 |
| 11 | 255.255.255.224 | 2046 | 30 |
| 12 | 255.255.255.240 | 4094 | 14 |
| 13 | 255.255.255.248 | 8190 | 6 |
| 14 | 255.255.255.252 | 16382 | 2 |
| Class C | |||
| # Bits | Subnet Mask | # Subnets | # Hosts |
| 24 | 255.255.255.0 | 1 | 254 |
| 25 | 255.255.255.128 | 2 | 126 |
| 26 | 255.255.255.192 | 4 | 62 |
| 27 | 255.255.255.224 | 8 | 30 |
| 28 | 255.255.255.240 | 16 | 14 |
| 29 | 255.255.255.248 | 32 | 6 |
| 30 | 255.255.255.252 | 64 | 2 |
| 31 | 255.255.255.254 | UNUSED | N/A |
| 32 | 255.255.255.255 | 255 | 1 |
Last Updated on 8/11/97
By Keith Sinclair
Email: keith@sinclair.org.au
All contents copyright © 1997 Keith Sinclair.