IP address
An IP address serves two principal functions. It identifies the host, or more specifically its network interface, and it provides the location of the host in the network, and thus the capability of establishing a path to that host. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."
The header of each IP packet contains the IP address of the sending host, and that of the destination host.
Subnetwork
The "routing prefix" may be expressed in Classless Inter-Domain Routing (CIDR) notation written as the first address of a network, followed by a slash character ("/"), and ending with the bit-length of the prefix. For example, is the prefix of the Internet Protocol version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing. Addresses in the range to belong to this subnet. The IPv6 address specification is a large address block with 2 addresses, having a 32-bit routing prefix.