IPv4 Address Types – Internet Protocol Version 4 (IPv4) Design

IPv4 addresses can be classified as one of three types: 

• Unicast
• Broadcast
• Multicast

A unicast address represents a single interface of a host (PC, router, or server). It can be a source or destination IP address. A broadcast address is a destination IP address that is set to all other devices in a given address range; normally, it is sent to all devices in the IP subnet. A multicast address is a destination IP address sent to a specific set of hosts. Table 1-11 summarizes IPv4 address types.

Table 1-11 IPv4 Address Types

IPv4 Private Addresses 

Some network numbers in the IPv4 address space are reserved for private use. These numbers are not routed on the Internet, so there is no way to reach them over an Internet connection. Many organizations today use private addresses in their internal networks with NAT to access the Internet. (NAT is covered later in this chapter.) Private addresses are explained in RFC 1918: Address Allocation for Private Internets, published in 1996. Creating private addresses was one of the first steps in dealing with the concern that the globally unique IPv4 address space would become exhausted. The availability of private addresses combined with NAT reduces the need for organizations to carefully define subnets to minimize the waste of assigned public global IP addresses.

The IP network address space reserved for private internetworks is 10/8, 172.16/12, and 192.168/16. It includes one Class A network, 16 Class B networks, and 256 Class C networks. Table 1-12 summarizes private address space. Large organizations can use network 10.0.0.0/8 to assign address space throughout the enterprise. Midsize organizations can use one of the Class B private networks 172.16.0.0/16 through 172.31.0.0/16 for IP addresses. The smaller Class C addresses, which begin with 192.168, can be used by corporations and are commonly used in home routers.

Table 1-12 IPv4 Private Address Space