CIDR
Technology & Computing abbreviation · Networking
| Stands for | Classless Inter-Domain Routing |
|---|---|
| Categories | Technology & Computing |
CIDR stands for Classless Inter-Domain Routing, a networking abbreviation.
A way of writing IP address ranges as an address plus a prefix length, such as 192.168.1.0/24, where /24 means the first 24 bits identify the network. CIDR replaced the rigid class A, B and C system in 1993, letting networks be sized to need.
Example: Allow SSH only from the office CIDR block 203.0.113.0/27 in the security group.
Usage notes
Introduced in RFCs 1518 and 1519 to slow IPv4 exhaustion and shrink internet routing tables through route aggregation. A /24 contains 256 addresses and a /32 is a single host. Pronounced "cider". Cloud consoles ask for CIDR notation when defining VPCs, subnets and firewall rules.
Related abbreviations
More networking abbreviations
- ARP – Address Resolution Protocol
- ARPANET – Advanced Research Projects Agency Network
- ASN – Autonomous system number
- ATM – Asynchronous Transfer Mode
- BGP – Border Gateway Protocol
- CGNAT – Carrier-grade NAT
- CIFS – Common Internet File System
- CNAME – Canonical name (record)
- CRC – Cyclic redundancy check
- CSMA/CD – Carrier-sense multiple access with collision detection
- DDNS – Dynamic DNS
- DHCP – Dynamic Host Configuration Protocol