CIDR Notation Chart

CIDR (Classless Inter-Domain Routing) notation is a compact way to specify IP address ranges and subnet masks. The number after the slash indicates how many bits of the address identify the network portion.

Complete IPv4 CIDR Reference

CIDR	Subnet Mask	Addresses	Usable Hosts	Class
/32	255.255.255.255	1	1	Host
/31	255.255.255.254	2	2*	P2P
/30	255.255.255.252	4	2	P2P
/29	255.255.255.248	8	6	C
/28	255.255.255.240	16	14	C
/27	255.255.255.224	32	30	C
/26	255.255.255.192	64	62	C
/25	255.255.255.128	128	126	C
/24	255.255.255.0	256	254	C
/23	255.255.254.0	512	510	2x C
/22	255.255.252.0	1,024	1,022	4x C
/21	255.255.248.0	2,048	2,046	8x C
/20	255.255.240.0	4,096	4,094	16x C
/19	255.255.224.0	8,192	8,190	32x C
/18	255.255.192.0	16,384	16,382	64x C
/17	255.255.128.0	32,768	32,766	128x C
/16	255.255.0.0	65,536	65,534	B
/15	255.254.0.0	131,072	131,070	2x B
/14	255.252.0.0	262,144	262,142	4x B
/13	255.248.0.0	524,288	524,286	8x B
/12	255.240.0.0	1,048,576	1,048,574	16x B
/11	255.224.0.0	2,097,152	2,097,150	32x B
/10	255.192.0.0	4,194,304	4,194,302	64x B
/9	255.128.0.0	8,388,608	8,388,606	128x B
/8	255.0.0.0	16,777,216	16,777,214	A
/7	254.0.0.0	33,554,432	33,554,430	2x A
/6	252.0.0.0	67,108,864	67,108,862	4x A
/5	248.0.0.0	134,217,728	134,217,726	8x A
/4	240.0.0.0	268,435,456	268,435,454	16x A
/3	224.0.0.0	536,870,912	536,870,910	32x A
/2	192.0.0.0	1,073,741,824	1,073,741,822	64x A
/1	128.0.0.0	2,147,483,648	2,147,483,646	128x A
/0	0.0.0.0	4,294,967,296	4,294,967,294	All IPv4

Common Use Cases

Cloud Provider Allocations

Use Case	Typical CIDR	Addresses	Notes
AWS VPC Default	/16	65,536	172.31.0.0/16
Kubernetes Pod Network	/16	65,536	10.244.0.0/16 typical
Docker Bridge Network	/16	65,536	172.17.0.0/16
Small Office	/24	256	192.168.1.0/24 typical
Router Link	/30 or /31	4 or 2	Point-to-point connections
Loopback/Host Route	/32	1	Single IP address

Subnet Mask Binary Breakdown

/24 = 255.255.255.0
      11111111.11111111.11111111.00000000
      |------- Network ---------|-- Host --|

/25 = 255.255.255.128
      11111111.11111111.11111111.10000000

/26 = 255.255.255.192
      11111111.11111111.11111111.11000000

/27 = 255.255.255.224
      11111111.11111111.11111111.11100000

/28 = 255.255.255.240
      11111111.11111111.11111111.11110000

IPv6 CIDR Quick Reference

CIDR	Addresses	Typical Use
/128	1	Single host
/64	18.4 quintillion	Standard subnet (required for SLAAC)
/56	256 x /64s	Typical ISP residential allocation
/48	65,536 x /64s	Enterprise/site allocation
/32	65,536 x /48s	ISP allocation from RIR