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.
Multicast address
IPv4 multicast addresses are defined by the most-significant bit pattern of "1110". This originates from the classful network design of the early Internet when this group of addresses was designated as "Class D". The CIDR notation for this group is . The group includes the addresses from to . Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) "Best Current Practice" document (BCP 51).