Multicast address
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, such as Ethernet multicast, and at the internet layer for Internet Protocol Version 4 or Version 6 multicast.
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.The address range is divided into blocks, each assigned a specific purpose or behavior.
| IP multicast address range | Description | Routable |
| 224.0.0.0 to 224.0.0.255 | Local subnetwork | |
| 224.0.1.0 to 224.0.1.255 | Internetwork control | |
| 224.0.2.0 to 224.0.255.255 | AD-HOC block 1 | |
| 224.1.0.0 to 224.1.255.255 | Reserved | |
| 224.2.0.0 to 224.2.255.255 | SDP/SAP block | |
| 224.3.0.0 to 224.4.255.255 | AD-HOC block 2 | |
| 224.5.0.0 to 224.255.255.255 | Reserved | |
| 225.0.0.0 to 231.255.255.255 | Reserved | |
| 232.0.0.0 to 232.255.255.255 | Source-specific multicast | |
| 233.0.0.0 to 233.251.255.255 | GLOP addressing | |
| 233.252.0.0 to 233.255.255.255 | AD-HOC block 3 | |
| 234.0.0.0 to 234.255.255.255 | Unicast-prefix–based | |
| 235.0.0.0 to 238.255.255.255 | Reserved | |
| 239.0.0.0 to 239.255.255.255 | Administratively scoped |
;Local subnetwork
;Internetwork control block
;AD-HOC block
;SDP/SAP block
;Source-specific multicast
;GLOP
;Unicast-prefix–based
;Administratively scoped
;Ethernet-specific
Notable IPv4 multicast addresses
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.| IP multicast address | Description | Routable |
| 224.0.0.0 | Base address | |
| 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 to address multicast routers. | |
| 224.0.0.5 | The Open Shortest Path First 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 address is used to send OSPF routing information to designated routers on a network segment. | |
| 224.0.0.9 | The Routing Information Protocol 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 group address is used to send routing information to all EIGRP routers on a network segment. | |
| 224.0.0.13 | Protocol Independent Multicast Version 2 | |
| 224.0.0.18 | Virtual Router Redundancy Protocol | |
| 224.0.0.19–21 | IS-IS over IP | |
| 224.0.0.22 | Internet Group Management Protocol version 3 | |
| 224.0.0.102 | Hot Standby Router Protocol version 2 / Gateway Load Balancing Protocol | |
| 224.0.0.107 | Precision Time Protocol version 2 peer delay measurement messaging | |
| 224.0.0.251 | Multicast DNS address | |
| 224.0.0.252 | Link-local Multicast Name Resolution 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 version 1 messages except peer delay measurement | |
| 224.0.1.129 | Precision Time Protocol version 2 messages except peer delay measurement | |
| 224.0.23.12 | KNXnet/IP discovery | |
| 239.255.255.250 | Simple [Service Discovery Protocol] address | |
| 239.255.255.253 | Service Location Protocol version 2 address |
IPv6
Multicast addresses in IPv6 use the prefix.Based on the value of the flag bits, IPv6 multicast addresses can be unicast-prefix–based multicast addresses, source-specific multicast addresses, or embedded–rendezvous-point IPv6 multicast addresses. Each of these types of multicast addresses have their own format and follow specific rules.
Similar to a unicast address, the prefix of an IPv6 multicast address specifies its scope; however, the set of possible scopes for a multicast address is different. The 4-bit scope field is used to indicate where the address is valid and unique.
| IPv6 address | IPv4 equivalent | Scope | Purpose |
| Reserved | - | ||
| Interface-local | Packets with this destination address may not be sent over any network link, but must remain within the current node; this is the multicast equivalent of the unicast loopback address. | ||
| Link-local | Packets with this destination address may not be routed anywhere. | ||
| Realm-Local scope | Local multicast particular to a network technology | ||
| Admin-local | The smallest scope that must be administratively configured. | ||
| Site-local | Restricted to the local physical network. | ||
| Organization-local | Restricted to networks used by the organization administering the local network. | ||
| Global scope | Eligible to be routed over the public internet. |
The service is identified in the group ID field. For example, if refers to all Network Time Protocol servers on the local network segment, then refers to all NTP servers in an organization's networks. The group ID field may be further divided for special multicast address types.
Notable IPv6 multicast addresses
The following table is a list notable IPv6 multicast addresses that are registered with IANA.To be included in some of the below multicast groups a client must send a Multicast Listener Discovery, a component of ICMPv6 suite, to join that group. For example, to listen to, a client must send a MLD report to the router, containing the multicast address, to indicate that it wants to listen to that group.
| Address | Description |
| All nodes on the local network segment | |
| All routers on the local network segment | |
| OSPFv3 All SPF routers | |
| OSPFv3 All DR routers | |
| IS-IS for IPv6 routers | |
| RIP routers | |
| EIGRP routers | |
| PIM routers | |
| Virtual Router Redundancy Protocol version 3 | |
| MLDv2 reports | |
| All DHCPv6 servers and relay agents on the local network segment | |
| All LLMNR hosts on the local network segment | |
| All DHCPv6 servers on the local network site | |
| Simple Service Discovery Protocol | |
| Multicast DNS | |
| Network Time Protocol | |
| Network Information Service | |
| Precision Time Protocol version 2 messages except peer delay measurement | |
| Precision Time Protocol version 2 peer delay measurement messages | |
| Used for experiments |
Ethernet
Ethernet frames with a value of 1 in the least-significant bit of the first octet of the destination MAC address are treated as multicast frames and are flooded to all points on the network. While frames with ones in all bits of the destination address are sometimes referred to as broadcasts, Ethernet generally does not distinguish between multicast and broadcast frames. Modern Ethernet controllers filter received packets to reduce CPU load by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.The IEEE has allocated the address block to for group addresses for use by standard protocols. Of these, the MAC group addresses in the range of to are not forwarded by 802.1D-conformant MAC bridges.