# subnet mask(서브넷 마스크) 비트 별 정리 #

bit	netmask	Cisco mask	hosts	usable hosts	Class
/4	240.0.0.0	15.255.255.255	268435456	268435454
/5	248.0.0.0	7.255.255.255	134217728	134217726
/6	252.0.0.0	3.255.255.255	67108864	67108862
/7	254.0.0.0	1.255.255.255	33554432	33554430
/8	255.0.0.0	0.255.255.255	16777216	16777214	A Class
/9	255.128.0.0	0.127.255.255	8388608	8388606
/10	255.192.0.0	0.63.255.255	4194304	4194302
/11	255.224.0.0	0.31.255.255	2097152	2097150
/12	255.240.0.0	0.15.255.255	1048576	1048574
/13	255.248.0.0	0.7.255.255	524288	524286
/14	255.252.0.0	0.3.255.255	262144	262142
/15	255.254.0.0	0.1.255.255	131072	131070
/16	255.255.0.0	0.0.255.255	65536	65534	B Class
/17	255.255.128.0	0.0.127.255	32768	32766
/18	255.255.192.0	0.0.63.255	16384	16382
/19	255.255.224.0	0.0.31.255	8192	8190
/20	255.255.240.0	0.0.15.255	4096	4094
/21	255.255.248.0	0.0.7.255	2048	2046
/22	255.255.252.0	0.0.3.255	1024	1022
/23	255.255.254.0	0.0.1.255	512	510
/24	255.255.255.0	0.0.0.255	256	254	C Class
/25	255.255.255.128	0.0.0.127	128	126
/26	255.255.255.192	0.0.0.63	64	62
/27	255.255.255.224	0.0.0.31	32	30
/28	255.255.255.240	0.0.0.15	16	14
/29	255.255.255.248	0.0.0.7	8	6
/30	255.255.255.252	0.0.0.3	4	2
/31	point to point links only
/32	255.255.255.255	use host notaition	1	1