ipv4 subnetting reference

Certain chunks of IPv4 address space are specially allocated by RFCs for special uses such as loopback, RFC 1918 networks, and Zeroconf usage, and are not available for allocation by Regional Internet Registries (RIRs). The netmask is a bitmask that can be used to separate the bits of the network identifier from the bits of the host identifier. It is often written in the same notation used to denote IP addresses. Not all sizes of prefix announcement may be routable on the public Internet: see routing, peering.

CIDR	Netmask	Hosts / subnet	Classful name	Typical usage
/8	255.0.0.0	16777216	Class A	Largest block allocation made by IANA
/9	255.128.0.0	8388608
/10	255.192.0.0	4194304
/11	255.224.0.0	2097152
/12	255.240.0.0	1048576
/13	255.248.0.0	524288
/14	255.252.0.0	262144
/15	255.254.0.0	131072
/16	255.255.0.0	65536	Class B
/17	255.255.128.0	32768		ISP / large business
/18	255.255.192.0	16384		ISP / large business
/19	255.255.224.0	8192		ISP / large business
/20	255.255.240.0	4096		Small ISP / large business
/21	255.255.248.0	2048		Small ISP / large business
/22	255.255.252.0	1024
/23	255.255.254.0	512
/24	255.255.255.0	256	Class C	Large LAN
/25	255.255.255.128	128		Large LAN
/26	255.255.255.192	64		Small LAN
/27	255.255.255.224	32		Small LAN
/28	255.255.255.240	16		Small LAN
/29	255.255.255.248	8
/30	255.255.255.252	4		"Glue network" (point to point links)
/31	255.255.255.254	2		"Useless Network", proposed for point to point links (RFC 3021)
/32	255.255.255.255	1		Host route

Ipv4 Subnetting Reference

See also