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 (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.<ref>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.</ref> The group includes the addresses from Template:IPaddr to Template:IPaddr.

The address range is divided into blocks each assigned a specific purpose or behavior.Template:Ref RFC

IP multicast address range	Description	Routable
224.0.0.0 to 224.0.0.255	Local subnetwork<ref name="Cisco Multicast">Template:Citation</ref>	Template:No
224.0.1.0 to 224.0.1.255	Internetwork control	Template:Yes
224.0.2.0 to 224.0.255.255	AD-HOC block 1<ref>AD-HOC Block 1</ref>	Template:Yes
224.1.0.0 to 224.1.255.255	ReservedTemplate:Ref RFC<ref name="IANA IP"/>
224.2.0.0 to 224.2.255.255	SDP/SAP block<ref>SDP/SAP Block</ref>	Template:Yes
224.3.0.0 to 224.4.255.255	AD-HOC block 2<ref>AD-HOC Block 2</ref>	Template:Yes
224.5.0.0 to 224.255.255.255	ReservedTemplate:Ref RFC<ref name="IANA IP"/>
225.0.0.0 to 231.255.255.255	ReservedTemplate:Ref RFC<ref name="IANA IP"/>
232.0.0.0 to 232.255.255.255	Source-specific multicast<ref name="Cisco Multicast"/>	Template:Yes
233.0.0.0 to 233.251.255.255	GLOP addressing<ref name=fall2011tcp>Template:Cite book</ref>	Template:Yes
233.252.0.0 to 233.255.255.255	AD-HOC block 3<ref>AD-HOC Block 3</ref>	Template:Yes
234.0.0.0 to 234.255.255.255	Unicast-prefix-based<ref>Unicast-Prefix-based IPv4 Multicast Addresses</ref>	Template:Yes
235.0.0.0 to 238.255.255.255	ReservedTemplate:Ref RFC<ref name="IANA IP"/>
239.0.0.0 to 239.255.255.255	Administratively scoped<ref name="Cisco Multicast"/>	Template:Yes

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.Template:Ref RFC

SDP/SAP block

Addresses in the reserved Template:IPaddr range are not individually assigned by IANA. Fallen out of use Template:Ref RFC for security considerations, experimental Session Announcement Protocol Template:Ref RFC was the primary means of supplying addresses through Session Description Protocol, which now is mostly used in the establishment of private sessions.

Source-specific multicast

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

GLOP<ref>Template:Cite book</ref>

The Template:IPaddr 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.Template:Ref RFC 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.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> The method is not applicable to the newer 32-bit ASNs. In Template:Date, the IETF envisioned a broader use of the range for many-to-many multicast applications.Template:Ref RFC Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.Template:Citation needed

Unicast-prefix-based

The Template:IPaddr range is assigned 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.Template:Ref RFC A resulting advantage over GLOP is that the unicast-prefix mechanism resembles the unicast-prefix capabilities of IPv6.Template:Ref RFC

Administratively scoped

The Template:IPaddr range is assigned for private use within an organization.Template:Ref 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 Template:IPaddr range may be structured to be loosely similar to the scoped IPv6 multicast address.Template:Ref RFC

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.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>{{ safesubst:#invoke:Unsubst||date=__DATE__ |$B= Template:Fix }}

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).<ref name="IANA IP"/>

IP multicast address	Description	Routable
224.0.0.0	Base address (reserved)	Template:No
224.0.0.1	The All Hosts multicast group addresses all hosts on the same network segment.	Template:No
224.0.0.2	The All Routers multicast group addresses all routers on the same network segment.	Template:No
224.0.0.4	This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers.	Template:No
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.	Template:No
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.	Template:No
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.	Template:No
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.	Template:No
224.0.0.13	Protocol Independent Multicast (PIM) Version 2	Template:No
224.0.0.18	Virtual Router Redundancy Protocol (VRRP)	Template:No
224.0.0.19–21	IS-IS over IP	Template:No
224.0.0.22	Internet Group Management Protocol (IGMP) version 3Template:Ref RFC	Template:No
224.0.0.102	Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)	Template:No
224.0.0.107	Precision Time Protocol (PTP) version 2 peer delay measurement messaging	Template:No
224.0.0.251	Multicast DNS (mDNS) address	Template:No
224.0.0.252	Link-local Multicast Name Resolution (LLMNR) address	Template:No
224.0.0.253	Teredo tunneling client discovery addressTemplate:Ref RFC	Template:No
224.0.1.1	Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode.	Template:Yes
224.0.1.22	Service Location Protocol version 1 general	Template:Yes
224.0.1.35	Service Location Protocol version 1 directory agent	Template:Yes
224.0.1.39	The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements.	Template:Yes
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.	Template:Yes
224.0.1.41	H.323 Gatekeeper discovery address	Template:Yes
224.0.1.129–132	Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement	Template:Yes
224.0.1.129	Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement	Template:Yes
224.0.23.12	KNXnet/IP discovery<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>	Template:Yes
239.255.255.250	Simple Service Discovery Protocol address	Template:Yes
239.255.255.253	Service Location Protocol version 2 address	Template:Yes

IPv6

Multicast addresses in IPv6 use the prefix Template:IPaddr.Template:Ref RFC Template:Trim

Based on the value of the flag bits, IPv6 multicast addresses can be Unicast-Prefix-based Multicast Addresses,Template:Ref RFC Source-Specific Multicast Addresses,Template:Ref RFC or Embedded RP IPv6 Multicast Addresses.Template:Ref RFC 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<ref group=note>x is a place holder indicating that the value of the flags field is unimportant in the current discussion.</ref>	IPv4 equivalentTemplate:Ref RFC	ScopeTemplate:Ref RFC	Purpose
Template:Mono		Reserved
Template:Mono		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.
Template:Mono	Template:Mono	Link-local	Packets with this destination address may not be routed anywhere.
Template:Mono	Template:Mono	Realm-Local scopeTemplate:Ref RFC	Local multicast particular to a network technology
Template:Mono		Admin-local	The smallest scope that must be administratively configured.
Template:Mono		Site-local	Restricted to the local physical network.
Template:Mono	Template:Mono	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.)
Template:Mono	Template:Mono	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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.Template:Ref RFC For example, to listen to Template:IPaddr, a client must send a MLD report to the router, containing the multicast address, to indicate that it wants to listen to that group.Template:Ref RFC

Address	Description
Template:Mono	All nodes on the local network segment
Template:Mono	All routers on the local network segment
Template:Mono	OSPFv3 All SPF routers
Template:Mono	OSPFv3 All DR routers
Template:Mono	IS-IS for IPv6 routers
Template:Mono	RIP routers
Template:Mono	EIGRP routers
Template:Mono	PIM routers
Template:Mono	Virtual Router Redundancy Protocol (VRRP) version 3
Template:Mono	MLDv2 reportsTemplate:Ref RFC
Template:Mono	All DHCPv6 servers and relay agents on the local network segmentTemplate:Ref RFC
Template:Mono	All LLMNR hosts on the local network segmentTemplate:Ref RFC
Template:Mono	All DHCPv6 servers on the local network siteTemplate:Ref RFC
Template:Mono	Simple Service Discovery Protocol
Template:Mono	Multicast DNS
Template:Mono	Network Time Protocol
Template:Mono	Network Information Service
Template:Mono	Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement
Template:Mono	Precision Time Protocol (PTP) version 2 peer delay measurement messages
Template:Mono	Used for experiments

Ethernet

Ethernet frames with a value of 1 in the least-significant bit of the first octet<ref group=note>On Ethernet, the least-significant bit of an octet is the first to be transmitted. A multicast is indicated by the first transmitted bit of the destination address being 1.</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Some well known Ethernet multicast addresses<ref>{{#invoke:citation/CS1|citation

CitationClass=web }}</ref>	Block	Ethernet multicast address	Ethertype	Usage
01-80-C2<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> 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<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref> ICANN/IANA	Template:Macaddr through Template:Macaddr	0x0800	IPv4 Multicast:Template:Ref RFC Insert the low 23 bits of the multicast IPv4 address into the Ethernet addressTemplate:Ref RFC
33-33-xx locally administered	Template:MACaddr through Template:MACaddr	0x86DD	IPv6 multicast:Template:Ref RFC The low 32 bits an Ethernet address for IPv6 multicast traffic are the low 32 bits of the multicast IPv6 address used.Template:Ref RFC 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 AddressTemplate:Citation needed

802.11

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

See also

• Broadcast address
• Reserved IP addresses