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DSL-504 ADSL Router User’s Guide

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

Cla

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.