A multicast address is a numerical 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 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 .MULTICAST_IP_ADDR. General Electric Digital Solutions. CIMPLICITY 10.0. In network prefix or Classless Inter-Domain Routing ( CIDR) notation, IP multicast addresses are summarized as 224.0.0.0/4. The group includes the addresses from to .
The address range is divided into blocks, each assigned a specific purpose or behavior. IP multicast address rangeDescriptionRoutable224.0.0.0 to 224.0.0.255Local subnetwork224.0.1.0 to 224.0.1.255Internetwork control224.0.2.0 to 224.0.255.255AD-HOC block 1AD-HOC Block 1224.1.0.0 to 224.1.255.255Reserved224.2.0.0 to 224.2.255.255SDP/SAP blockSDP/SAP Block224.3.0.0 to 224.4.255.255AD-HOC block 2AD-HOC Block 2224.5.0.0 to 224.255.255.255Reserved225.0.0.0 to 231.255.255.255Reserved232.0.0.0 to 232.255.255.255Source-specific multicast233.0.0.0 to 233.251.255.255GLOP addressing233.252.0.0 to 233.255.255.255AD-HOC block 3AD-HOC Block 3234.0.0.0 to 234.255.255.255Unicast-prefix–basedUnicast-Prefix–Based IPv4 Multicast Addresses235.0.0.0 to 238.255.255.255Reserved239.0.0.0 to 239.255.255.255Administratively scoped
Local subnetwork Addresses in the range of to are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses , Open Shortest Path First (OSPF) uses and , and Multicast DNS uses . Routers must not forward these messages outside the subnet from which they originate.
Internetwork control block Addresses in the range to are individually assigned by IANA and designated as 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 using .
AD-HOC block Addresses in three separate blocks are not individually assigned by IANA. These addresses are globally routed and are used for applications that don't fit either of the previously described purposes.
SDP/SAP block Addresses in the reserved range are not individually assigned by IANA. Fallen out of use for security considerations, experimental Session Announcement Protocol was the primary means of supplying addresses through Session Description Protocol, which is now mostly used in the establishment of private sessions.
Source-specific multicast The (IPv4) and (IPv6) blocks are reserved for use by source-specific multicast.
GLOP The range was originally assigned as an experimental, public statically-assigned multicast address space for publishers and Internet service providers that wished to source content on the Internet. The allocation method is termed GLOP addressing and provides implementers a block of 255 addresses that is determined by their 16-bit autonomous system number (ASN) allocation. In a nutshell, the middle two octets of this block are formed from assigned ASNs, giving any operator assigned an ASN 256 globally unique multicast group addresses. The method is not applicable to the newer 32-bit ASNs. In , the IETF envisioned a broader use of the range for many-to-many multicast applications. Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.
Unicast-prefix–based The range is assigned as a range of global IPv4 multicast address space provided to each organization that has or larger globally routed unicast address space allocated; one multicast address is reserved per of unicast space. A resulting advantage over GLOP is that the unicast-prefix mechanism resembles the unicast-prefix capabilities of IPv6.
Administratively scoped The range is assigned for private use within an organization. Packets destined to administratively scoped IPv4 multicast addresses do not cross administratively defined organizational boundaries, and administratively scoped IPv4 multicast addresses are locally assigned and do not have to be globally unique. The range may be structured to be loosely similar to the scoped IPv6 multicast address.
Ethernet-specific In support of link-local multicasts which do not use IGMP, any IPv4 multicast address that falls within the and ranges will be broadcast to all ports on many Ethernet switches, even if IGMP snooping is enabled, so addresses within these ranges should be avoided on Ethernet networks where the functionality of IGMP snooping is desired.
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 (IANA).
IP multicast addressDescriptionRoutable224.0.0.0Base address (reserved)224.0.0.1The All Hosts multicast group addresses all hosts on the same network segment.224.0.0.2The All Routers multicast group addresses all routers on the same network segment.224.0.0.4This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers.224.0.0.5The Open Shortest Path First (OSPF) All OSPF Routers address is used to send Hello packets to all OSPF routers on a network segment.224.0.0.6The OSPF All Designated Routers (DR) address is used to send OSPF routing information to designated routers on a network segment.224.0.0.9The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment.224.0.0.10The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.224.0.0.13Protocol Independent Multicast (PIM) Version 2224.0.0.18Virtual Router Redundancy Protocol (VRRP)224.0.0.19–21IS-IS over IP224.0.0.22Internet Group Management Protocol (IGMP) version 3224.0.0.102Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)224.0.0.107 Precision Time Protocol (PTP) version 2 peer delay measurement messaging224.0.0.251Multicast DNS (mDNS) address224.0.0.252Link-local Multicast Name Resolution (LLMNR) address224.0.0.253Teredo tunneling client discovery address224.0.1.1Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode.224.0.1.22Service Location Protocol version 1 general224.0.1.35Service Location Protocol version 1 directory agent224.0.1.39The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements.224.0.1.40The Cisco multicast router AUTO-RP-DISCOVERY address is the destination address for messages from the RP mapping agent to discover candidates.224.0.1.41H.323 Gatekeeper discovery address224.0.1.129–132Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement224.0.1.129Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement224.0.23.12KNXnet/IP discovery239.255.0.0-239.255.249.255sACN (streaming ACN) ANSI E1.31 standard. Used by all sACN-capable lighting consoles for multicast of lighting control data of 1 to 63,999 DMX512 universes, as a multicast (non-RDM) alternative to Artnet broadcast. Designed by the Entertainment Services and Technology Association (ESTA). Refer public tool to translate between sACN DMX universe number versus multicast IP. 239.255.255.250Simple Service Discovery Protocol address239.255.255.253Service 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 (bits 12 to 15) is used to indicate where the address is valid and unique.
+Multicast address scopeIPv6 addressIPv4 equivalentScopePurposeReservedInterface-localPackets 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-localPackets with this destination address may not be routed anywhere.Realm-Local scopeLocal multicast particular to a network technologyAdmin-localThe smallest scope that must be administratively configured.Site-localRestricted to the local physical network.Organization-localRestricted to networks used by the organization administering the local network. (For example, these addresses might be used over VPNs; when packets for this group are routed over the public internet (where these addresses are not valid), they would have to be encapsulated in some other protocol.)Global scopeEligible 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 (NTP) 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 (MLD), 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 (VRRP) 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 (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement Precision Time Protocol (PTP) 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.
+Some well known Ethernet multicast addressesBlockEthernet multicast addressEthertypeUsage01-80-C2