Classless Inter-Domain Routing: Difference between revisions

Revision as of 14:46, 4 May 2025

Revision as of 10:16, 5 May 2025

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In routed subnets larger than {{IPaddr||31}} or {{IPaddr||32}}, the number of available host addresses is usually reduced by two, namely the largest address, which is reserved as the [[broadcast address]], and the smallest address, which identifies the network itself.<ref name="RFC 922">{{cite IETF |rfc=922 |title=Broadcasting Internet Datagrams in the Presence of Subnets |editor=J. Mogul |date=October 1984 |section=7}}</ref><ref name="RFC 1812">{{cite IETF |rfc=1812 |title=Requirements for IP Version 4 Routers |editor=F. Baker |date=June 1995 |section=4.2.3.1}}</ref>

inIn such usage, a {{IPaddr||31}} network, with one binary digit in the host identifier, is unusable, as such a subnet would provide no available host addresses after this reduction. {{IETF RFC|3021}} creates an exception to the "host all ones" and "host all zeros" rules to make {{IPaddr||31}} networks usable for point-to-point links. {{IPaddr||32}} addresses (single-host network) must be accessed by explicit routing rules, as there is no address available for a gateway.

===IPv6 CIDR blocks===