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I S P  G L O S S A R Y
Your source for the most up-to-date terms, definitions, and acronyms for and about internet service providers.

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CIDR
Last modified: Friday, November 07, 2003 

Short for Classless Inter-Domain Routing, an IP addressing scheme that replaces the older system based on classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP network prefix. For example:

172.200.0.0/16

The IP network prefix specifies how many addresses are covered by the CIDR address, with lower numbers covering more addresses. An IP network prefix of /12, for example, can be used to address 1,048,576 former Class C addresses.

CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations.

CIDR is also called supernetting.

  Related Links

CIDR overview 
Overview of CIDR with links to related Request for Comments documents. This page is hosted by Pacific Bell Internet.

Related Categories

Addressing

Internet Protocols

Related Terms

DDR

hot potato routing

IP address

routing

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