A multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service. Multicast addressing can be used in the Link Layer (Layer 2 in the OSI model), such as Ethernet multicast, and at the Internet Layer (Layer 3 for OSI) for Internet Protocol Version 4 (IPv4) or Version 6 (IPv6) multicast.
IPv4
IPv4 multicast addresses are defined by the leading address bits of 1110, originating from the classful network design of the early Internet when this group of addresses was designated as Class D. The Classless Inter-Domain Routing (CIDR) prefix of this group is 224.0.0.0/4. The group includes the addresses from 224.0.0.0 to 239.255.255.255. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) Best Current Practice document (BCP 51).
The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicasting and that are registered with the Internet Assigned Numbers Authority (IANA).
| IP multicast address | Description |
|---|---|
| 224.0.0.0 | Base address (reserved) |
| 224.0.0.1 | The All Hosts multicast group addresses all hosts on the same network segment. |
| 224.0.0.2 | The All Routers multicast group addresses all routers on the same network segment. |
| 224.0.0.4 | This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers. |
| 224.0.0.5 | The Open Shortest Path First (OSPF) All OSPF Routers address is used to send Hello packets to all OSPF routers on a network segment. |
| 224.0.0.6 | The OSPF All Designated Routers ""(DR)"" address is used to send OSPF routing information to designated routers on a network segment. |
| 224.0.0.9 | The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment. |
| 224.0.0.10 | The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment. |
| 224.0.0.13 | Protocol Independent Multicast (PIM) Version 2 |
| 224.0.0.18 | Virtual Router Redundancy Protocol (VRRP) |
| 224.0.0.19 - 21 | IS-IS over IP |
| 224.0.0.22 | Internet Group Management Protocol (IGMP) version 3 |
| 224.0.0.102 | Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP) |
| 224.0.0.107 | Precision Time Protocol (PTP) version 2 peer delay measurement messaging |
| 224.0.0.251 | Multicast DNS (mDNS) address |
| 224.0.0.252 | Link-local Multicast Name Resolution (LLMNR) address |
| 224.0.0.253 | Teredo tunneling client discovery address |
| 224.0.1.1 | Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode. |
| 224.0.1.22 | Service Location Protocol version 1 general |
| 224.0.1.35 | Service Location Protocol version 1 directory agent |
| 224.0.1.39 | The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements. |
| 224.0.1.40 | The Cisco multicast router AUTO-RP-DISCOVERY address is the destination address for messages from the RP mapping agent to discover candidates. |
| 224.0.1.41 | H.323 Gatekeeper discovery address |
| 224.0.1.129 - 132 | Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement |
| 224.0.1.129 | Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement |
| 239.255.255.250 | Simple Service Discovery Protocol address |
| 239.255.255.253 | Service Location Protocol version 2 address |
Local subnetwork
Addresses in the range of 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Zeroconf mDNS uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate.
Internetwork control block
Addresses in the range 224.0.1.0 to 224.0.1.255 are individually assigned by IANA and designated the Internetwork Control Block. This block of addresses is used for traffic that must be routed through the public Internet, such as for applications of the Network Time Protocol (224.0.1.1).
