Classless Inter-Domain Routing

lastmod 2024-05-31created 2015-07-139 edits

CIDR (Classless Inter-Domain Routing) is a classless inter-domain routing technique and a modern IP address allocation method that began to be introduced in 1993. CIDR replaced network classes, the previous IP address allocation scheme. CIDR adds flexibility compared to the previous scheme when dividing an IP address space into multiple network ranges. In particular, it has the following advantages.

• It allows the rapidly dwindling IPv4 addresses to be used more efficiently.
• It reduces the burden of Internet-wide routing by using a hierarchical structure with prefix-based addressing.

Notation

• The slash after an IP Address - CIDR Notation

IP/MaskNumber

For example, it is written as 192.168.0.0/16. /16 indicates the bit length of the Korean: 서브넷 마스크.

For reference, in the commonly used 192.168.0.xxx/24, the first 24 bits are the bit and mask used to obtain the subnet, and the trailing xxx becomes the host number.

See also

• DNS
• IP
• Subnetwork/Subnet mask
• ipcalc - IP calculator. Calculates host ranges, netmasks, etc.

Favorite site

• Wikipedia (en) description of CIDR
• Zetawiki: CIDR
• A summary of the CIDR ("cider") technique :: Jins' Dev Inside

Online Tools

• Online IP Subnet Calculator and CIDR Calculator