IPv4 Subnet Directory/8 – /32

IPv4 CIDR & Subnet Mask Reference

Deterministic reference guide for all IPv4 subnet masks from /8 to /32. Compare total address pools, usable host capacities, wildcard masks, and RFC 3021 point-to-point configurations.

Standard LAN Subnets

Common local development, VPC private subnets, and office networks.

/16 /24 /28

Point-to-Point Links

RFC 3021 point-to-point router interfaces and isolated single hosts.

/30 /31 /32

Large ISP & Enterprise

High-capacity CIDR allocations for cloud VPCs and routing backbones.

/8 /12 /20

Complete IPv4 CIDR Reference Table

25 Subnet Blocks

Prefix	Subnet Mask	Wildcard Mask	Total IPs	Usable Hosts	Guide
/8	255.0.0.0	0.255.255.255	16,777,216	16,777,214	Inspect
/9	255.128.0.0	0.127.255.255	8,388,608	8,388,606	Inspect
/10	255.192.0.0	0.63.255.255	4,194,304	4,194,302	Inspect
/11	255.224.0.0	0.31.255.255	2,097,152	2,097,150	Inspect
/12	255.240.0.0	0.15.255.255	1,048,576	1,048,574	Inspect
/13	255.248.0.0	0.7.255.255	524,288	524,286	Inspect
/14	255.252.0.0	0.3.255.255	262,144	262,142	Inspect
/15	255.254.0.0	0.1.255.255	131,072	131,070	Inspect
/16	255.255.0.0	0.0.255.255	65,536	65,534	Inspect
/17	255.255.128.0	0.0.127.255	32,768	32,766	Inspect
/18	255.255.192.0	0.0.63.255	16,384	16,382	Inspect
/19	255.255.224.0	0.0.31.255	8,192	8,190	Inspect
/20	255.255.240.0	0.0.15.255	4,096	4,094	Inspect
/21	255.255.248.0	0.0.7.255	2,048	2,046	Inspect
/22	255.255.252.0	0.0.3.255	1,024	1,022	Inspect
/23	255.255.254.0	0.0.1.255	512	510	Inspect
/24	255.255.255.0	0.0.0.255	256	254	Inspect
/25	255.255.255.128	0.0.0.127	128	126	Inspect
/26	255.255.255.192	0.0.0.63	64	62	Inspect
/27	255.255.255.224	0.0.0.31	32	30	Inspect
/28	255.255.255.240	0.0.0.15	16	14	Inspect
/29	255.255.255.248	0.0.0.7	8	6	Inspect
/30	255.255.255.252	0.0.0.3	4	2	Inspect
/31	255.255.255.254	0.0.0.1	2	2	Inspect
/32	255.255.255.255	0.0.0.0	1	1	Inspect

Frequently Asked Questions

What is CIDR notation?

Classless Inter-Domain Routing (CIDR) notation expresses an IP address and its associated routing prefix using a slash followed by the prefix length in bits (for example, 192.168.1.0/24).

How do I calculate usable hosts in a subnet?

For standard IPv4 subnets (/0 to /30), the formula for usable hosts is 2^(32 - prefix) - 2, subtracting 2 for the network and broadcast addresses. Under RFC 3021, /31 point-to-point links allow 2 usable host addresses with no dedicated broadcast.

What is a wildcard mask?

A wildcard mask is the inverted representation of a subnet mask (255.255.255.255 minus the subnet mask), commonly used in Cisco access control lists (ACLs) and OSPF configuration.