Multicast - Local Network Control Block
The Multicast range of addresses used in IPv4 are defined as 224.0.0.0/4. Of this range, the 224.0.0.0/24 subnet is known as the Local Network Control Block.
These are addresses used for protocol control traffic including OSPF, EIGRP, and others. Specific addresses within the range are reserved for use with various protocols. These multicast addresses are non-routable, meaning they will never be routed outside of the local subnet, nor will they be advertised. They are also ignored by the IGMP protocol, so on a switch they are always broadcast to all hosts within the network segment.