What does network number, network prefix, CIDR prefix, subnet mask, netmask mean

Last Modified: Fri, 21 Mar 2014 20:39:20 +0000 ; Created: Fri, 21 Mar 2014 18:40:02 +0000

Doing some research on the origins of some common Internet terms for networking. Not a lot to go on as formal definitions in standard documents versus common usage vary. The terms themselves are used in different forms even in the same RFC document.

RFC4632 - Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan.

network number (or prefix) - which bits in a 32-bit IPv4 address are interpreted as the network number (or prefix) associated with a site

Also known as "network identifier" but not defined so in RFC.

network address is a common known term as well, but that was actually the term used in the old classful (or class based) system. The newer term for CIDR is prefixes. RFC4632: "The solution that the community created was to deprecate the Class A/B/C network address assignment system in favor of using "classless", hierarchical blocks of IP addresses (referred to as prefixes)."

CIDR prefix = 4 octets/mask (example:

RFC1812 has the following definition:

Network Prefix

The portion of an IP Address that signifies a set of systems. It is selected from the IP Address by logically ANDing a subnet mask with the address, or (equivalently) setting the bits of the address not among the most significant bits of the address to zero.

RFC950 - Internet Standard Subnetting Procedure

subnet address mask (a.k.a. address mask). RFC is for IPv4

The terms "network mask" or "netmask" never appear in this RFC. "network mask" appears in RFC4632. "netmask" is a common abbreviation.

RFC950 specifies a 32-bit address mask field. One common example would be the 4 octet decimal dotted form:

RFC4291 - IP Version 6 Addressing Architecture

node's subnet prefix (a.k.a. subnet number) - CIDR prefix form of the network number or prefix. Suitable for IPv6 and IPv4 (RFC4632).

Example: 2001:0DB8:0000:CD30:0000:0000:0000:0000/60