What is a subnet mask?

A subnet mask is a 32-bit value that separates the network portion from the host portion of an IP address using bitwise AND.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of a subnet mask. It is used in Cisco ACLs and OSPF to match IP ranges flexibly.

How many hosts can a /24 support?

254 usable hosts. A /24 provides 256 total addresses, minus 2 for network and broadcast.

What are RFC 1918 private IP ranges?

10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C) are reserved for private networks.

What CIDR do I need for 1000 devices?

A /22 provides 1,022 usable hosts, which is sufficient for 1,000 devices with room for growth.

Is this cheat sheet printable?

Yes. The table is responsive and can be printed directly from your browser. A PDF version is also available from the Subnet Mask Table tutorial page.

Subnet Cheat Sheet

Quick reference for CIDR notation, subnet masks, wildcard masks, and host counts. Bookmark this page for your CCNA exam prep. The chart below covers all 25 CIDR prefixes from /8 to /32, showing the corresponding subnet mask, wildcard mask, number of usable hosts, total hosts, and binary mask representation. Private IP ranges per RFC 1918 are also included so you can quickly identify non-public address space. Each table row includes complete subnetting parameters that you can verify using our subnet calculator for real-time IP address calculations.

CIDR Reference Chart

Complete reference from /8 to /32. Subnet mask, wildcard mask, and usable host counts.

CIDR Chart — Subnet Mask, Wildcard Mask & Usable Hosts
CIDR	Subnet Mask	Wildcard Mask	Usable Hosts	Notation
/8	255.0.0.0	0.255.255.255	16,777,214	/8
/9	255.128.0.0	0.127.255.255	8,388,606	/9
/10	255.192.0.0	0.63.255.255	4,194,302	/10
/11	255.224.0.0	0.31.255.255	2,097,150	/11
/12	255.240.0.0	0.15.255.255	1,048,574	/12
/13	255.248.0.0	0.7.255.255	524,286	/13
/14	255.252.0.0	0.3.255.255	262,142	/14
/15	255.254.0.0	0.1.255.255	131,070	/15
/16	255.255.0.0	0.0.255.255	65,534	/16
/17	255.255.128.0	0.0.127.255	32,766	/17
/18	255.255.192.0	0.0.63.255	16,382	/18
/19	255.255.224.0	0.0.31.255	8,190	/19
/20	255.255.240.0	0.0.15.255	4,094	/20
/21	255.255.248.0	0.0.7.255	2,046	/21
/22	255.255.252.0	0.0.3.255	1,022	/22
/23	255.255.254.0	0.0.1.255	510	/23
/24	255.255.255.0	0.0.0.255	254	/24
/25	255.255.255.128	0.0.0.127	126	/25
/26	255.255.255.192	0.0.0.63	62	/26
/27	255.255.255.224	0.0.0.31	30	/27
/28	255.255.255.240	0.0.0.15	14	/28
/29	255.255.255.248	0.0.0.7	6	/29
/30	255.255.255.252	0.0.0.3	2	/30
/31	255.255.255.254	0.0.0.1	2	/31
/32	255.255.255.255	0.0.0.0	0	/32

Private IPv4 Address Ranges (RFC 1918)

RFC 1918 Private IPv4 Address Ranges
Class	CIDR	Range	Approx. Hosts
A	10.0.0.0/8	10.0.0.0 – 10.255.255.255	16.7 million
B	172.16.0.0/12	172.16.0.0 – 172.31.255.255	1.0 million
C	192.168.0.0/16	192.168.0.0 – 192.168.255.255	65,536

Common Subnetting Patterns

Common Subnet Sizing Patterns
Need	Min CIDR	Example Use Case
2 hosts	/30	Point-to-point WAN links
6 hosts	/29	Small office subnet
14 hosts	/28	Branch office subnet
30 hosts	/27	Medium department
62 hosts	/26	Large department
126 hosts	/25	Small building
254 hosts	/24	Typical campus subnet
1,022 hosts	/22	Enterprise floor

Want a printable version?

📥 PDF download available at Subnet Mask Table