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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 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 Template:IPaddr. The group includes the addresses from Template:IPaddr to Template:IPaddr. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) Best Current Practice document (BCP 51).

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	否
224.0.1.0 to 224.0.1.255	Internetwork control	是
224.0.2.0 to 224.0.255.255	AD-HOC block 1	是
224.1.0.0 to 224.1.255.255	Reserved
224.3.0.0 to 224.4.255.255	AD-HOC block 2	是
225.0.0.0 to 231.255.255.255	Reserved
232.0.0.0 to 232.255.255.255	Source-specific multicast	是
233.0.0.0 to 233.251.255.255	GLOP addressing	是
233.252.0.0 to 233.255.255.255	AD-HOC block 3	是
234.0.0.0 to 234.255.255.255	Unicast-prefix-based	是
235.0.0.0 to 238.255.255.255	Reserved
239.0.0.0 to 239.255.255.255	Administratively scoped	是

Local subnetwork

Addresses in the range of Template:IPaddr to Template:IPaddr are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses Template:IPaddr, Open Shortest Path First (OSPF) uses Template:IPaddr and Template:IPaddr, and Multicast DNS uses Template:IPaddr. Routers must not forward these messages outside the subnet from which they originate.

Internetwork control block

Addresses in the range Template:IPaddr to Template:IPaddr 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 Template:IPaddr.

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.

Source-specific multicast

The Template:IPaddr (IPv4) and Template:IPaddr (IPv6) blocks are reserved for use by source-specific multicast.

GLOP

The Template:IPaddr range was originally assigned by RFC 2770 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. RFC 3180, superseding RFC 2770, envisioned the 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 Template:IPaddr range is assigned by RFC 6034 as a range of global IPv4 multicast address space provided to each organization that has Template:IPaddr or larger globally routed unicast address space allocated; one multicast address is reserved per Template:IPaddr of unicast space. A resulting advantage over GLOP is that the unicast-prefix mechanism resembles the unicast-prefix capabilities of IPv6 as defined in RFC 3306.

Administratively scoped

The Template:IPaddr range is assigned by RFC 2365 for private use within an organization. Per the RFC, 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 RFC also discusses structuring the Template:IPaddr range to be loosely similar to the scoped IPv6 multicast address range described in RFC 1884.

Ethernet-specific

In support of link-local multicasts which do not use IGMP, any IPv4 multicast address that falls within the Template:IPaddr and Template:IPaddr 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.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 (IANA).

IP multicast address	Description	Routable
224.0.0.0	Base address (reserved)	否
224.0.0.1	The All Hosts multicast group addresses all hosts on the same network segment.	否
224.0.0.2	The All Routers multicast group addresses all routers on the same network segment.	否
224.0.0.4	This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers.	否
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.	否
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.	否
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.	否
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.	否
224.0.0.13	Protocol Independent Multicast (PIM) Version 2	否
224.0.0.18	Virtual Router Redundancy Protocol (VRRP)	否
224.0.0.19–21	IS-IS over IP	否
224.0.0.22	Internet Group Management Protocol (IGMP) version 3	否
224.0.0.102	Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)	否
224.0.0.107	Precision Time Protocol (PTP) version 2 peer delay measurement messaging	否
224.0.0.251	Multicast DNS (mDNS) address	否
224.0.0.252	Link-local Multicast Name Resolution (LLMNR) address	否
224.0.0.253	Teredo tunneling client discovery address	否
224.0.1.1	Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode.	是
224.0.1.22	Service Location Protocol version 1 general	是
224.0.1.35	Service Location Protocol version 1 directory agent	是
224.0.1.39	The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements.	是
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.	是
224.0.1.41	H.323 Gatekeeper discovery address	是
224.0.1.129–132	Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement	是
224.0.1.129	Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement	是
239.255.255.250	Simple Service Discovery Protocol address	是
239.255.255.253	Service Location Protocol version 2 address	是

IPv6

Multicast addresses in IPv6 use the prefix Template:IPaddr. The general format of the IPv6 multicast address is described by RFC 4291:

General multicast address format

Bits	8	4	4	112
Field	prefix	flags	scope	group ID

Multicast address flags

Bit	Flag	0	1
0 (MSB)	Reserved	(Reserved)	(Reserved)
1	R (Rendezvous)	Rendezvous point not embedded	Rendezvous point embedded
2	P (Prefix)	Without prefix information	Address based on network prefix
3 (LSB)	T (Transient) You are invited to add it here.	Well-known multicast address	Dynamically assigned multicast address

Based on the value of the flag bits, IPv6 multicast addresses can be Unicast-Prefix-based Multicast Addresses, Source-Specific Multicast Addresses (both types introduced by RFC 3306, updated by RFC 7371), or Embedded RP IPv6 Multicast Addresses (introduced by RFC 3956, updated by RFC 7371). 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 scope

IPv6 address	IPv4 equivalent	Scope You are invited to add it here.	Purpose
ffx0::/16, ffxf::/16		Reserved
ffx1::/16		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.
ffx2::/16	224.0.0.0/24	Link-local	Packets with this destination address may not be routed anywhere.
ffx3::/16	239.255.0.0/16	Realm-Local scope You are invited to add it here.	Local multicast particular to a network technology
ffx4::/16		Admin-local	The smallest scope that must be administratively configured.
ffx5::/16		Site-local	Restricted to the local physical network.
ffx8::/16	239.192.0.0/14	Organization-local	Restricted 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.)
ffxe::/16	224.0.1.0-238.255.255.255	Global scope	Eligible to be routed over the public internet.

The service is identified in the group ID field. For example, if Template:IPaddr refers to all Network Time Protocol (NTP) servers on the local network segment, then Template:IPaddr 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 ff02::1:ff28:9c5a, 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
ff02::1	All nodes on the local network segment
ff02::2	All routers on the local network segment
ff02::5	OSPFv3 All SPF routers
ff02::6	OSPFv3 All DR routers
ff02::8	IS-IS for IPv6 routers
ff02::9	RIP routers
ff02::a	EIGRP routers
ff02::d	PIM routers
ff02::12	Virtual Router Redundancy Protocol (VRRP) version 3
ff02::16	MLDv2 reports You are invited to add it here.
ff02::1:2	All DHCPv6 servers and relay agents on the local network segment You are invited to add it here.
ff02::1:3	All LLMNR hosts on the local network segment You are invited to add it here.
ff05::1:3	All DHCPv6 servers on the local network site You are invited to add it here.
ff0x::c	Simple Service Discovery Protocol
ff0x::fb	Multicast DNS
ff0x::101	Network Time Protocol
ff0x::108	Network Information Service
ff0x::181	Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement
ff02::6b	Precision Time Protocol (PTP) version 2 peer delay measurement messages
ff0x::114	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 (Template:Macaddr) 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 Template:Macaddr to Template:Macaddr for group addresses for use by standard protocols. Of these, the MAC group addresses in the range of Template:Macaddr to Template:Macaddr are not forwarded by 802.1D-conformant MAC bridges.

Some well known Ethernet multicast addresses

Block	Ethernet multicast address	Ethertype	Usage
01-80-C2 IEEE (802 group)		Local LAN Segment, stopping at STP-capable switches
		SNAP (length)	Spanning Tree Protocol (for bridges) IEEE 802.1D
		0x88CC	Link Layer Discovery Protocol (additional)
	Template:Macaddr	0x8808	Ethernet flow control (pause frame) IEEE 802.3x
	Template:Macaddr	0x8809	"Slow protocols" including Ethernet OAM Protocol (IEEE 802.3ah) and Link Aggregation Control Protocol (LACP)
		Local LAN Segment until next multi-port ("non-TPMR") switch
		0x888E	Port authentication (IEEE 802.1X EAPOL)
		0x88CC	Link Layer Discovery Protocol (additional)
	Template:Macaddr	SNAP (length)	Spanning Tree Protocol (for provider bridges) IEEE 802.1ad
	Template:Macaddr	0x88F5	Multiple VLAN Registration Protocol (for provider bridges) IEEE 802.1ad
	Template:Macaddr	Local LAN Link, never crosses another device
		0x88CC	Link Layer Discovery Protocol (primary)
		0x88F7	Precision Time Protocol (PTP) version 2 over Ethernet (802.1AS)
	Template:Macaddr	0x88F5	GARP VLAN Registration Protocol (also known as IEEE 802.1Q GVRP) Multiple VLAN Registration Protocol (MVRP)
	Template:Macaddr through Template:Macaddr	0x8902	Ethernet CFM Protocol IEEE 802.1ag
01-1B-19 IEEE (TC9)	Template:Macaddr	0x88F7	Precision Time Protocol (PTP) version 2 over Ethernet (native layer-2) for electing the Grandmaster clock and advanced applications, otherwise Template:Macaddr
01-00-5E ICANN/IANA	Template:Macaddr through Template:Macaddr	0x0800	IPv4 Multicast (RFC 1112), insert the low 23 bits of the multicast IPv4 address into the Ethernet address
33-33-xx locally administered	Template:Macaddr through Template:Macaddr	0x86DD	IPv6 multicast (RFC 2464): The low 32 bits an Ethernet address for IPv6 multicast traffic are the low 32 bits of the multicast IPv6 address used. For example, IPv6 multicast traffic using the address Template:IPaddr uses the MAC address Template:Macaddr, and traffic to Template:IPaddr goes to the MAC address Template:Macaddr.
01-0C-CD IEC	Template:Macaddr through Template:Macaddr	0x88B8	IEC 61850-8-1 GOOSE Type 1/1A
	Template:Macaddr through Template:Macaddr	0x88B9	GSSE (IEC 61850 8-1)
	Template:Macaddr through Template:Macaddr	0x88BA	Multicast sampled values (IEC 61850 8-1)
01-00-0C Cisco Systems	Template:Macaddr	SNAP (length)	Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Unidirectional_Link_Detection (UDLD)
	Template:Macaddr	SNAP (length)	Cisco Shared Spanning Tree Protocol Address

802.11

802.11 wireless networks use the same MAC addresses for multicast as Ethernet.

See also

• Broadcast address
• Reserved IP addresses