Special Addresses

Special Addresses

In classful addressing some addresses were reserved for special purposes. The classless addressing scheme inherits some of these addresses from classful addressing.

Special Blocks

Some blocks of address are reserved for special purposes. 

All-Zero Address

The block 0.0.0.0/32, is reserved for communication when a host needs to send an IPv4 packet but it does not know its own address. 

This is normally used host at bootstrap time when it does not know its IPv4 address. The host send an IPv4 packet to bootstrap server using this address as the source address and a limited broadcast address as the destination address to find its own address. 

All-0nes Address: Limited Broadcast Address

The block 255.255.255.255/32, is reserved for limited broadcast address in the current network. 

A host wants to send a message to every other host can use this address as destination address in an IPv4 packet. 

Loopback Addresses

The block 127.0.0.0/8 is used for the loopback address, which is an address used to test the software on a machine.

When loopback address is used, the packet never leaves the machine, it simply returns to the protocol software.

The loopback address can be used by a client process to send a message to a server process on the same machine.

Private Addresses 

A number of blocks are assigned for private use. These addresses are used either in isolation or in connection with network address translation techniques. 

 

 Multicast Addresses

The block 224.0.0.0/4 is reserved for multicast communication.

Special Addresses in Each block

Some address in a block be used for special addresses. These address are not assigned to any host.

Network Address 

The first address in a block defines the network/subnetwork address. It defines the network/subnetwork itself and not any host in the network. 

Direct Broadcast Address

The last address in a block or subblock can be used as a direct broadcast address. This address is usually used by a router to send a packet to all hosts in a specific network.  All hosts will accept a packet having this type of destination address. 

This address can be used only as a destination address in a IPv4 address.