IPv4 地址转换器

Q: What is the difference between decimal, hex and binary forms?

They are the same 32 bits written three ways. `192.168.1.1` is `3232235777` in decimal, `c0:a8:01:01` in hex, and `11000000.10101000.00000001.00000001` in binary.

把 IPv4 地址转为十进制、十六进制、二进制和 CIDR 表示，查看子网范围、地址类别与是否为内网地址。

The 32-bit model

An IPv4 address is 32 bits, usually written as four decimal octets. Each octet is 8 bits and ranges from 0 to 255.

192.168.1.1
  |  |  |  |
  |  |  |  +-- 1   = 0x01
  |  |  +----- 1   = 0x01
  |  +-------- 168 = 0xA8
  +----------- 192 = 0xC0

The same address in binary is 11000000.10101000.00000001.00000001, and in hex it is C0A80101.

Address classes

Class	First octet	Purpose
A	1–126	Large networks
B	128–191	Medium networks
C	192–223	Small networks
D	224–239	Multicast
E	240–255	Reserved / experimental

Classful addressing is obsolete — CIDR replaced it in 1993 — but the labels persist in documentation and exam material.

Private ranges

Range	RFC	Use
`10.0.0.0/8`	RFC 1918	Large private networks
`172.16.0.0/12`	RFC 1918	Medium private networks
`192.168.0.0/16`	RFC 1918	Small private networks (home routers)
`127.0.0.0/8`	RFC 1122	Loopback (`127.0.0.1` = localhost)
`169.254.0.0/16`	RFC 3927	Link-local / APIPA

Anything in these ranges is not routable on the public internet. 192.168.x.x is the range most home routers hand out via DHCP.

Common gotchas

127.0.0.1 is localhost; 0.0.0.0 means "all interfaces" when binding a server, and is not a valid destination address
255.255.255.255 is the limited broadcast address
Leading zeros are ambiguous — some parsers treat 010.1.1.1 as octal
The loopback range 127.0.0.0/8 is entirely reserved, not just 127.0.0.1

常见问题

How is an IPv4 address stored?

As 32 bits, usually written as four decimal octets. Each octet is 8 bits and ranges from 0 to 255.

What is the difference between decimal, hex and binary forms?

They are the same 32 bits written three ways. 192.168.1.1 is 3232235777 in decimal, c0:a8:01:01 in hex, and 11000000.10101000.00000001.00000001 in binary.

What does the tool detect about my address?

Whether it falls in a private range, is a loopback address, or is link-local, plus its class and the host range of a /24 subnet.

Is 0.0.0.0 a valid destination?

No. It is a special value meaning "all interfaces" when binding a server, and it is not routable as a destination address.

What is 127.0.0.1?

The loopback address, pointing back at your own machine. The entire 127.0.0.0/8 range is reserved, not just that one address.