Class D and E:
Class D is a class with first 4 MSB (Most significance bit) set to
According to IANA (Internet Assigned Numbers Authority), there are three specific IP address blocks reserved and able to be used for extending internal network. We call it Private IP address and list below:
Class A | 10.0.0.0 | 10.255.255.255 | |
Class B | 172.16.0.0 | 172.31.255.255 | |
Class C | 192.168.0.0 | 192.168.255.255 |
Please refer to RFC 1597 and RFC 1466 for more information. Subnet mask:
It means the
For a class B network, 128.1.2.3, it may have a subnet mask 255.255.0.0 in default, in which the first two bytes is with all 1s. This means more than 60 thousands of nodes in flat IP address will be at the same network. It’s too large to manage practically. Now if we divide it into smaller network by extending network prefix from 16 bits to, say 24 bits, that’s using its third byte to subnet this class B network. Now it has a subnet mask 255.255.255.0, in which each bit of the first three bytes is 1. It’s now clear that the first two bytes is used to identify the class B network, the third byte is used to identify the subnet within this class B network and, of course, the last byte is the host number.
Not all IP address is available in the
128.1.2.128/25
Network
Subnet
10000000.00000001.00000010.1 0000000
25 bits
All 0s = 128.1.2.128 All 1s= 128.1.2.255
10000000
11111111
18