Special IPv4 Addresses

IPv4 Broadcast Addresses

A broadcast address is the address used to represent broadcasts to the network. A broadcast means that data is simultaneously sent to all hosts on the LAN. In most systems, the default broadcast address is the address with a host number of all ones (255). An example of a broadcast address is :

Note : The broadcast address is computed by applying another set of binary functions to the netmask and network number (the logical NOT operator applied to the netmask followed by the logical OR of the resulting value with the network number). For further discussion of these and other operations, see TCP/IP Addressing, by Buck Graham.

Reserved Network and Host IPv4 Values

Certain values associated with IPv4 addresses are reserved for specific purposes. Tese are defined in the following table :

IPv4 Address Description
127.x.x.xReserved for loopback.
Network Number followed by all bits set to 0Network address, such as
Network Number followed by all bits set to 1Broadcast address, such as address used by systems that do not yet know its own IP address. Protocals such as RARP and BOOTP use this address when attempting to communicate with a server. broadcast.

There is a range of network addresses that IANA has set aside for private use and therefore packets addressed to them are not routed between real Internet sites. They are:

Class A
Class B172.16.0.0 through
Class C192.168.0.0 through

However be carefull, hosts with such addresses should not even be connected to the Internet. Note : For a more thorough treatment, seeRFC #1597 and RFC #1627