IPv4 multicast addresses are defined as Class D addresses. The Internet Assigned Numbers Authority (IANA) reserves all addresses whose first four bits are '1110' for this purpose. This bit pattern results in a first octet value ranging from 224 (11100000) to 239 (11101111). Therefore, the entire IPv4 multicast address range is 224.0.0.0 to 239.255.255.255, which is also commonly represented in CIDR notation as 224.0.0.0/4.

A. The first 3 bits of the address set to '110' defines Class C unicast addresses (192.0.0.0 to 223.255.255.255), not multicast addresses.

B. The multicast address range begins at 224.0.0.0. The range specified (starting at 223.0.0.0) incorrectly includes a Class C unicast address.

C. The first 4 bits of the address set to '1111' defines Class E addresses (240.0.0.0 to 255.255.255.255), which are reserved for experimental use.

D. Subnet masks are used with unicast addresses to separate the network and host portions. Multicast addresses identify a group of recipients and do not have this structure.

1. Internet Engineering Task Force (IETF) RFC 1112, "Host Extensions for IP Multicasting":

Section 4, "IP Multicast Addresses", Page 5: "Class D addresses are used for IP multicasting. The high-order four bits of a Class D address are 1110. The remaining 28 bits identify the multicast "group" to which the datagram is sent." This directly supports option E.

2. Internet Engineering Task Force (IETF) RFC 5771, "IANA Guidelines for IPv4 Multicast Addresses":

Section 2, "The IPv4 Multicast Address Space", Page 2: "The range of IPv4 addresses from 224.0.0.0 to 239.255.255.255 is registered with IANA as the 'IPv4 Multicast Address Space'... This address range is also known as 'Class D'." This document reaffirms the address range defined by the '1110' prefix.

3. Nokia 4A0-108 Course Material (Nokia Interior Routing Protocols):

Module: IP Multicast Fundamentals: The course material explicitly defines the Class D address range (224.0.0.0/4) for multicast and specifies that these addresses are identified by the leading bit pattern '1110'. This is a foundational concept covered in the curriculum for this certification.