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Windows Server 2012 R2 Inside Out: Networking with TCP/IP

Special IPv4 addressing rules

As you’ve seen, certain IPv4 addresses and address ranges have special uses:

  • The addresses 127.0.0.0 through 127.255.255.255 are reserved for local loopback.
  • The addresses 10.0.0.0 through 10.255.255.255, 172.16.0.0 through 172.31.255.255, and 192.168.0.0 through 192.168.255.255 are designated as private and, as such, are nonroutable.
  • On classful networks, the Class A addresses w.255.255.255, the Class B addresses w.x.255.255, and the Class C addresses w.x.y.255 are reserved for broadcasts.
  • On nonclassful networks, the broadcast address is the last IPv4 address in the range of IPv4 addresses for the associated subnet.

On classful networks, all the bits in the network ID can’t be set to 0 because this expression is reserved to indicate a host on a local network. Similarly, on a classful network all the bits in the host ID can’t be set to 0 because this is reserved to indicate the IPv4 network number.

Table 2-3 lists the ranges of network numbers based on address classes. You can’t assign the network number to a network interface. The network number is common to all network interfaces attached to the same logical network. On a nonclassful network, the network number is the first IPv4 address in the range of IPv4 addresses for the associated subnet—as specified in RFC 1812.

Table 2-3 Network IDs for classful networks

Address Class

First Network Number

Last Network Number

Class A

1.0.0.0

126.0.0.0

Class B

128.0.0.0

191.255.0.0

Class C

192.0.0.0

223.255.255.0

When you apply all the rules for IPv4 addresses, you find that hosts on a network can’t use many IPv4 addresses. This means that the first available host ID and last available host ID are different from the range of available IPv4 addresses. Table 2-4 shows how these rules apply to classful networks. On a nonclassful network, the same rules apply—you lose the first and last available host IDs from the range of available IPv4 addresses.

Table 2-4 Available host IDs on classful networks

Address Class

First Host ID

Last Host ID

Class A

w.0.0.1

w.255.255.254

Class B

w.x.0.1

w.x.255.254

Class C

w.x.y.1

w.x.y.254