Netmask Cheat Sheet

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# bits	 # hosts	Usable hosts	netmask	 		Cisco mask
/4	 268435456	268435454	240.0.0.0		15.255.255.255
/5	 134217728	134217726	248.0.0.0		7.255.255.255
/6	 67108864	67108862	252.0.0.0		3.255.255.255
/7	 33554432	33554430	254.0.0.0		1.255.255.255
/8	 16777216	16777214	255.0.0.0		class A network .255.255.255
/9	 8388608	8388606	 	255.128.0.0		0.127.255.255
/10	 4194304	4194302	 	255.192.0.0		0.63.255.255
/11	 2097152	2097150	 	255.224.0.0		0.31.255.255
/12	 1048576	1048574	 	255.240.0.0		0.15.255.255
/13	 524288	        524286	 	255.248.0.0		0.7.255.255
/14	 262144	 	262142	 	255.252.0.0		0.3.255.255
/15	 131072	 	131070		255.254.0.0		0.1.255.255
/16	 65536	 	65534	 	255.255.0.0		class B network	 0.0.255.255
/17	 32768	 	32766	 	255.255.128.0		0.0.127.255
/18	 16384	 	16382	 	255.255.192.0		0.0.63.255
/19	 8192	 	8190	 	255.255.224.0		0.0.31.255
/20	 4096	 	4094	 	255.255.240.0		0.0.15.255
/21	 2048	 	2046		255.255.248.0		0.0.7.255
/22	 1024	 	1022		255.255.252.0		0.0.3.255
/23	 512	 	510		255.255.254.0		0.0.1.255
/24	 256	 	254		255.255.255.0		class C network	 0.0.0.255
/25	 128	 	126		255.255.255.128		0.0.0.127
/26	 64	 	62	 	255.255.255.192		0.0.0.63
/27	 32	 	30	 	255.255.255.224		0.0.0.31
/28	 16	 	14	 	255.255.255.240		0.0.0.15
/29	 8	 	6	 	255.255.255.248		0.0.0.7
/30	 4	 	2	 	255.255.255.252		0.0.0.3
/31	 point to point links only
/32	 1	 	1	 	255.255.255.255		single IP address	use host notation