## How many people here failed basic net address 101 class?

decimal representation of IP address is four numbers (eg 100.102.103.104) each group goes from 0 to 256. Due to management reasons two addresses are reserved within every network or sub-network, so the available numbers for use in any group is two less, or only 254 for a Class A. 8 bits to the byte means 2 to the 8th power, minus two unique addresses for admin = 254 not 127 as set out in the question.

Class A means the IP address is in the first group (100 above - shown as 100.xxx.xxx.xxx) and all the options available in the other three groups are part of it. Thus a class 1 address has only 254 available address, but within that Class A address the owner has 254 x 254 x 254 address available to them to use, or 16,387,064 addresses within their own group.

Class B means the IP address is a sub-group of a Class A and is in the second group (102 above - shown as 100.102.xxx.xxx ) and with 254 options within that sub group, but has 254 x 254 addresses open to it to use, or 64,516 addresses within it's group.

Class C means the IP address is a sub-group of Class B and is in the third group (103 above - shown as 100.102.103.xxx) and has only 254 options within that sub-group and only 254 address open to use within it.

Class D is a sub-net of Class C and reduces one more binary spot within the Class C, and Class E is the same again but down another binary spot. Total for a Class D is 128 - 2 or 126 addresses while Class E is 64 - 2 or 62 addresses.
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Now having said all that, some address ranges are reserved and will NOT be recognised by Internet routers because of that.
The 127.0.0.0 is admin reserved; the 10.xxx.xxx.xxx is the Class A internal network reserved; there is a Class B reserved one that I can't remember off hand, but think it may be 172.1.xxx.xxx; there is a Class C reserved of 192.168.0.xxx - - in each of these the x represents a number where you can substitute your own for use on your internal network.