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Next: 2.15 What is the Up: 2 Getting Started Previous: 2.13 I want to

2.14 What are CIDR netmasks?

(Excerpt from url: http://public.pacbell.net/dedicated/cidr.html)

CIDR is a new addressing scheme for the Internet which allows for more i efficient allocation of IP addresses than the old Class A, B, and C address scheme.

CIDR Block Equivalent Class C Addresses
/27 1/8th of a Class C 32 hosts
/26 1/4th of a Class C 64 hosts
/25 1/2 of a Class C 128 hosts
/24 1 Class C 256 hosts
/23 2 Class C 512 hosts
/22 4 Class C 1,024 hosts
/21 8 Class C 2,048 hosts
/20 16 Class C 4,096 hosts
/19 32 Class C 8,192 hosts
/18 64 Class C 16,384 hosts
/17 128 Class C 32,768 hosts
/16 256 Class C 65,536 hosts
/15 512 Class C 131,072 hosts
/14 1,024 Class C 262,144 hosts
/13 2,048 Class C 524,288 hosts

For more detailed technical information on CIDR, check out the following RFCs:

  • RFC 1517: Applicability Statement for the Implementation of CIDR
  • RFC 1518: An Architecture for IP Address Allocation with CIDR
  • RFC 1519: CIDR: An Address Assignment and Aggregation Strategy
  • RFC 1520: Exchanging Routing Information Across Provider Boundaries in the CIDR Environment

RFCs are available at http://www.rfc-editor.org/rfcsearch.html

next up previous
Next: 2.15 What is the Up: 2 Getting Started Previous: 2.13 I want to
Nigel Houghton 2006-10-02
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