# Appendix D. IP Addresses and Ranges Format

# IPv4 Addresses and Ranges

An IPv4 address is made of 4 numbers separated by dots as in `aaa.bbb.ccc.ddd`, each number ranges from 0 to 255.

An IPv4 address range must conform to one of the following forms:

- `*`: the range includes all valid IP addresses,

- `aaa.*`: the range includes the IPv4 addresses which first part is equal to `aaa`,

- `aaa.bbb.*`: the range includes the IPv4 addresses which first and second parts are respectively equal to `aaa` and `bbb`,

- `aaa.bbb.ccc.*`: the range includes the IPv4 addresses which first, second, and third parts are respectively equal to `aaa`, `bbb`, and `ccc`,

- `aaa.bbb.ccc.ddd-iii.jjj.kkk.lll`: the range includes the IPv4 addresses between `aaa.bbb.ccc.ddd` and `iii.jjj.kkk.lll`,

- `aaa.bbb.ccc.ddd/n`: the range includes all the IPv4 addresses that belong to the subnet which network prefix or CIDR (Classless Interdomain Routing) notation is `aaa.bbb.ccc.ddd/n`. An IPv4 address that is included in this range has its first `n` bits identical to the first `n` bits of `aaa.bbb.ccc.ddd`,

- `aaa.bbb.ccc.ddd-iii.jjj.kkk.lll/n`: An IPv4 address that is included in this range is comprised between `aaa.bbb.ccc.ddd` and `iii.jjj.kkk.lll`, and has its first `n` bits identical to the first `n` bits of `aaa.bbb.ccc.ddd` and `iii.jjj.kkk.lll`.

Example D-1. CIDR Notation Example

`220.78.168.0/21` represents IPv4 addresses between `220.78.168.0` and `220.78.175.255`. Actually, 220.78.168.0 in binary is 11011100 01001110 10101000 00000000. So `220.78.168.0/21` includes all the IPv4 addresses which 21 first bits are 11011100 01001110 10101. Therefore, it represents the range `220.78.168.0-220.78.175.255` (in binary 11011100 01001110 10101000 00000000 - 11011100 01001110 10101111 11111111.)