서브넷(subnet)

서브넷팅 계산 공식  2^x -2 = Y 

x = 호스트 비트수 
-2 = (Network ID, boradcast 주소)
Y = 필요한 IP 갯수

 

121.160.42.0    <- 네트워크 ID
121.160.42.11   <-  255.255.255.0
121.160.42.255  <- 서브넷 브로드케스트 주소

서브넷 마스크	Prefix mask	설정 가능한 ip주소 개수
255.255.255.255	/32
255.255.255.0	/24	2^8 - 2 = 254
255.255.0.0	/16	2^16 - 2 = 65,534
255.0.0.0	/8	2^24 - 2 = 16,777,214
0.0.0.0	/0
255.255.255.252	/30	2^2 -2 = 2
255.255.255.240	/28	2^4 -2 = 14
255.255.255.224	/27	2^5 -2 = 30
255.255.255.xxx	/26	2^6 -2 = 62
255.255.255.128	/25	2^7 -2 = 126
255.255.254.0	/23	2^9 -2 = 510
255.255.248.0	/21	2^11 -2 = 2046

 

@공인 ip 주소 

- 인터넷이 가능한 ip 주소 (isp 업체로부터 임대)

A class  0.0.0.0 ~ 127.255.255.255
B class  128.16.0.0 ~ 191.31.255.255
C class  192.0.0.0 ~ 223.168.255.255

@사설 ip 주소

- 내부용으로 사용하는 ip주소 (isp 임대 X)

A class 10.0.0.0 ~ 10.255.255.255
B class  172.16.0.0 ~ 172.31.255.255
C class  192.168.0.0 ~ 192.168.255.255