9.2 | Internet Addresses | |||
9.2.5 | Reserved IP addresses |
Certain host addresses are reserved and
cannot be assigned to devices on a network. These reserved host
addresses include the following:
An IP address that has binary 0s in all host bit positions is reserved for the network address. In a Class A network example, 113.0.0.0 is the IP address of the network, known as the network ID, containing the host 113.1.2.3. A router uses the network IP address when it forwards data on the Internet. In a Class B network example, the address 176.10.0.0 is a network address, as shown in Figure . In a Class B network address, the first two octets are designated as the network portion. The last two octets contain 0s because those 16 bits are for host numbers and are used to identify devices that are attached to the network. The IP address, 176.10.0.0, is an example of a network address. This address is never assigned as a host address. A host address for a device on the 176.10.0.0 network might be 176.10.16.1. In this example, “176.10” is the network portion and “16.1” is the host portion. To send data to all the devices on a network, a broadcast address is needed. A broadcast occurs when a source sends data to all devices on a network. To ensure that all the other devices on the network process the broadcast, the sender must use a destination IP address that they can recognize and process. Broadcast IP addresses end with binary 1s in the entire host part of the address. In the network example, 176.10.0.0, the last 16 bits make up the host field or host part of the address. The broadcast that would be sent out to all devices on that network would include a destination address of 176.10.255.255. This is because 255 is the decimal value of an octet containing 11111111.
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