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DI-304/DI-304M ISDN Remote Router
Networks attached to the Internet are assigned class types that determine the
maximum number of possible hosts per network. The previous figure illustrates how
the net and host portions of the IP address differ among the three classes. Class A is
assigned to networks that have more than 65,535 hosts; Class B is for networks that
have 256 to 65534 hosts; Class C is for networks with less than 256 hosts.
IP Network Classes
Class Maximum
Number of
Networks in
Class
Network Addresses (Host
Portion in Parenthesis)
Maximum
Number of
Hosts per
Network
A 126 1(.0.0.0) to 126(.0.0.0) 16,777,214
B 16,382 128.1(.0.0) to 191.254(.0.0) 65,534
C 2,097,150 192.0.1(.0) to 223.255.254(.0) 254
Note: All network addresses outside of these ranges (Class D and E) are either
reserved or set aside for experimental networks or multicasting.
When an IP address's host portion contains only zero(s), the address identifies a
network and not a host. No physical device may be given such an address.
The network portion must start with a value from 1 to 126 or from 128 to 223. Any
other value(s) in the network portion may be from 0 to 255, except that in class B
the network addresses 128.0.0.0 and 191.255.0.0 are reserved, and in class C the
network addresses 192.0.0.0 and 223.255.255.0 are reserved.
The value(s) in the host portion of a physical device's IP address can be in the range
of 0 through 255 as long as this portion is not all-0 or all-255. Values outside the
range of 0 to 255 can never appear in an IP address (0 to 255 is the full range of
integer values that can be expressed with eight bits).
The network portion must be the same for all the IP devices on a discrete physical
network (a single Ethernet LAN, for example, or a WAN link). The host portion
must be different for each IP device — or, to be more precise, each IP-capable port
or interface — connected directly to that network.
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