子網路subnet相關資訊

0 AND 0 = 0

0 AND 1 = 0

1 AND 1 = 1

0 OR 0   = 0

0 OR 1   = 1

1 OR 1   = 1

               Net ID       Host ID

A class    00000000.00000000.00000000.00000000

               Net ID                        Host ID

B class    10000000.00000000.00000000.00000000

               Net ID                                         Host ID

C class    11000000.00000000.00000000.00000000

A Class – 00000001到011111110
B Class – 10000001到101111110
C Class – 11000001到110111110

Host ID      =    先將netmask NOT，再與ip AND

broadcast  =    先將netmask NOT，再與ip OR

EXAMPLE1:
IP                    = 128.128.128.128 -> 10000000.10000000.10000000.10000000
Netmask         = 255.255.0.0         -> 11111111.11111111.00000000.00000000
 
NetID(subnet) = IP AND Netmask  -> 10000000.10000000.00000000.00000000 -> 128.128.0.0
HostID            = NOT Netmask       -> 00000000.00000000.11111111.11111111 -> AND IP -> 00000000.00000000.10000000.10000000 -> 0.0.128.128
Broadcast       = NOT Netmask       -> 00000000.00000000.11111111.11111111 -> OR IP   -> 10000000.10000000.11111111.11111111 -> 128.128.255.255

EXAMPLE2:
139.175.152.254/255.255.0.0
   ->   10001011.10101111.10011000.11111110
          11111111.11111111.00000000.00000000

Net = ip AND netmask -> 10001011.1010111.00000000.00000000 = 139.175.0.0

HOST = NOT netmask -> 00000000.00000000.11111111.11111111
                                       10001011.10101111.10011000.11111110
                    AND IP    -> 00000000.00000000.10011000.11111110->0.0.152.254

Broadcast = NOT netmask -> 00000000.00000000.11111111.11111111
                                              10001011.10101111.10011000.11111110   
                              OR IP  ->  10001011.10101111.11111111.11111111 = 139.175.255.255

二進位換成十進位
   10011101 -> 2⁷+0⁶+0⁵+2⁴+2³+2²+0¹+2⁰=128+0+0+16+8+4+0+1=157

十進位換成二進位
   157/2
   78/2  餘1
   39/2  餘0
   19/2  餘1
   9/2    餘1
   4/2    餘1
   2/2    餘0
   1       餘0

network id             全1            -> broadcast擴播

host id                    全1           -> 識別網路 ex:10.130.1.0 表network id為10.130.1.z的網段

network id host id  全0           -> 0.0.0.0 裝置本身

host id                    全1           -> broadcast ex:203.74.205.255 表203.74.205.0這網段的廣播封包

host id network id  全1           -> limited/local broadcast ex:255.255.255.255 限同一網段

network id 除prefix 其餘全1     -> loopback ex:127.x.y.z 191.255.x.y 223.255.255.z

C class
 203.66.77.0/255.255.255.0
 11001011.01000010.01001101.00000000/11111111.11111111.11111111.00000000

從Netmask借3bit割成8(2³)個子網路
<————————SubnetID————————> <-HostID->
1 1 1 1 1 1 1 1.1 1 1 1 1 1 1 1.1 1 1 1 1 1 1 1.1 1 1 0 0 0 0 0   -> 255.255.255.224

有八個子網路，每個子網路有30主機(2⁵-2)，會扣掉兩個是因為203.66.77.00000000(subnet)與203.66.77.00011111(broadcast)不能用
 203.66.77.00000001到.00011110(1到30)
 203.66.77.00100001到.00111110(33到62)
 203.66.77.01000001到.01011110(65到94)
 203.66.77.01100001到.01111110(97到126)
 203.66.77.10000001到.10011110(129到158)
 203.66.77.10100001到.10111110(161到190)
 203.66.77.11000001到.11011110(193到222)
 203.66.77.11100001到.11111110(225到254)

B Class
   139.175.152.254/255.255.0.0
      -> 10001011.10101111.10011000.11111110/11111111.11111111.0000000.00000000
           

                                                           借三個 bits    11111111.11111111.1110000.00000000
                                                           Netmask = 255.255.224.0
   Subnet為

      10001011.10101111.00000000.00000000(139.175.0.0)
      10001011.10101111.00100000.00000000(139.175.32.0)
      10001011.10101111.01000000.00000000(139.175.64.0)
      10001011.10101111.01100000.00000000(139.175.96.0)
      10001011.10101111.10000000.00000000(139.175.128.0)
      10001011.10101111.10100000.00000000(139.175.160.0)
      10001011.10101111.11000000.00000000(139.175.192.0)
      10001011.10101111.11100000.00000000(139.175.224.0)

   IP為
      139.175.00000000.00000001到139.175.00011111.11111110
      139.175.00100000.00000001到139.175.00111111.11111110
      139.175.01000000.00000001到139.175.01011111.11111110
      139.175.01100000.00000001到139.175.01111111.11111110
      139.175.10000000.00000001到139.175.10011111.11111110
      139.175.10100000.00000001到139.175.10111111.11111110
      139.175.11000000.00000001到139.175.11011111.11111110
      139.175.11100000.00000001到139.175.11111111.11111110