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 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 22.214.171.124/4. The group includes the addresses from 126.96.36.199 to 188.8.131.52. 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|
|184.108.40.206 to 220.127.116.11||Local subnetwork||No|
|18.104.22.168 to 22.214.171.124||Internetwork control||Yes|
|126.96.36.199 to 188.8.131.52||AD-HOC block 1||Yes|
|184.108.40.206 to 220.127.116.11||Reserved|
|18.104.22.168 to 22.214.171.124||AD-HOC block 2||Yes|
|126.96.36.199 to 188.8.131.52||Reserved|
|184.108.40.206 to 220.127.116.11||Source-specific multicast||Yes|
|18.104.22.168 to 22.214.171.124||GLOP addressing||Yes|
|126.96.36.199 to 188.8.131.52||AD-HOC block 3||Yes|
|184.108.40.206 to 220.127.116.11||Unicast-prefix-based||Yes|
|18.104.22.168 to 22.214.171.124||Reserved|
|126.96.36.199 to 188.8.131.52||Administratively scoped||Yes|
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|
|184.108.40.206||Base address (reserved)||No|
|220.127.116.11||The All Hosts multicast group addresses all hosts on the same network segment.||No|
|18.104.22.168||The All Routers multicast group addresses all routers on the same network segment.||No|
|22.214.171.124||This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers.||No|
|126.96.36.199||The Open Shortest Path First (OSPF) All OSPF Routers address is used to send Hello packets to all OSPF routers on a network segment.||No|
|188.8.131.52||The OSPF All Designated Routers (DR) address is used to send OSPF routing information to designated routers on a network segment.||No|
|184.108.40.206||The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment.||No|
|220.127.116.11||The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.||No|
|18.104.22.168||Protocol Independent Multicast (PIM) Version 2||No|
|22.214.171.124||Virtual Router Redundancy Protocol (VRRP)||No|
|126.96.36.199–21||IS-IS over IP||No|
|188.8.131.52||Internet Group Management Protocol (IGMP) version 3||No|
|184.108.40.206||Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)||No|
|220.127.116.11||Precision Time Protocol (PTP) version 2 peer delay measurement messaging||No|
|18.104.22.168||Multicast DNS (mDNS) address||No|
|22.214.171.124||Link-local Multicast Name Resolution (LLMNR) address||No|
|126.96.36.199||Teredo tunneling client discovery address||No|
|188.8.131.52||Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode.||Yes|
|184.108.40.206||Service Location Protocol version 1 general||Yes|
|220.127.116.11||Service Location Protocol version 1 directory agent||Yes|
|18.104.22.168||The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements.||Yes|
|22.214.171.124||The Cisco multicast router AUTO-RP-DISCOVERY address is the destination address for messages from the RP mapping agent to discover candidates.||Yes|
|126.96.36.199||H.323 Gatekeeper discovery address||Yes|
|188.8.131.52–132||Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement||Yes|
|184.108.40.206||Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement||Yes|
|220.127.116.11||Simple Service Discovery Protocol address||Yes|
|18.104.22.168||Service Location Protocol version 2 address||Yes|
Multicast addresses in IPv6 use the prefix ff00::/8. IPv6 multicast addresses can be structured using the old format (RFC 2373) or the new format (RFC 3306, updated by RFC 7371).
|Field||prefix||ff1||scope||ff2||reserved||plen||network prefix||group ID|
The prefix holds the value ff for all multicast addresses.
Currently, 3 of the 4 flag bits in the flags field (ff1) are defined; the most-significant flag bit is reserved for future use. The other three flags are known as R, P and T. All 4 bits in the additional flags field (ff2) are reserved for future use and must hold the value 0.
|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)||Well-known multicast address||Dynamically assigned multicast address|
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 sc (or scope) field (bits 12 to 15) is used to indicate where the address is valid and unique.
|IPv6 address[note 2]||IPv4 equivalent||Scope||Purpose|
|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||22.214.171.124/24||Link-local||Packets with this destination address may not be routed anywhere.|
|ffx3::/16||126.96.36.199/16||Realm-Local scope||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||188.8.131.52/14||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||184.108.40.206-220.127.116.11||Global scope||Eligible to be routed over the public internet.|
The service is identified in the group ID field. For example, if ff02::101 refers to all Network Time Protocol (NTP) servers on the local network segment, then ff08::101 refers to all NTP servers in an organization's networks. The group ID field may be further divided for special multicast address types.
The following table is a list notable IPv6 multicast addresses that are registered with IANA.
|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::12||Virtual Router Redundancy Protocol (VRRP) version 3|
|ff02::1:2||All DHCPv6 servers and relay agents on the local network segment|
|ff02::1:3||All LLMNR hosts on the local network segment|
|ff05::1:3||All DHCPv6 servers on the local network site|
|ff0x::c||Simple Service Discovery Protocol|
|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 frames with a value of 1 in the least-significant bit of the first octet[note 3] 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 (FF-FF-FF-FF-FF-FF) 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 01-80-C2-00-00-00 to 01-80-C2-FF-FF-FF for group addresses for use by standard protocols. Of these, the MAC group addresses in the range of 01-80-C2-00-00-00 to 01-80-C2-00-00-0F are not forwarded by 802.1D-conformant MAC bridges.
|Block||Ethernet multicast address||Ethertype||Usage|
|Local LAN Segment, stopping at STP-capable switches|
|SNAP (length)||Spanning Tree Protocol (for bridges) IEEE 802.1D|
|0x88CC||Link Layer Discovery Protocol (additional)|
|01-80-C2-00-00-01||0x8808||Ethernet flow control (pause frame) IEEE 802.3x|
|01-80-C2-00-00-02||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)|
|01-80-C2-00-00-08||SNAP (length)||Spanning Tree Protocol (for provider bridges) IEEE 802.1ad|
|01-80-C2-00-00-0D||0x88F5||Multiple VLAN Registration Protocol (for provider bridges) IEEE 802.1ad|
|01-80-C2-00-00-0E||Local LAN Link, never crosses another device|
|0x88CC||Link Layer Discovery Protocol (primary)|
|0x88F7||Precision Time Protocol (PTP) version 2 over Ethernet (802.1AS)|
|01-80-C2-00-00-21||0x88F5||GARP VLAN Registration Protocol (also known as IEEE 802.1Q GVRP)|
Multiple VLAN Registration Protocol (MVRP)
|0x8902||Ethernet CFM Protocol IEEE 802.1ag|
|01-1B-19-00-00-00||0x88F7||Precision Time Protocol (PTP) version 2 over Ethernet (native layer-2)|
for electing the Grandmaster clock and advanced applications, otherwise 01-80-C2-00-00-0E
|0x0800||IPv4 Multicast (RFC 1112), insert the low 23 bits of the multicast IPv4 address into the Ethernet address|
|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 ff02::d uses the MAC address 33-33-00-00-00-0D, and traffic to ff05::1:3 goes to the MAC address 33-33-00-01-00-03.|
|0x88B8||IEC 61850-8-1 GOOSE Type 1/1A|
|0x88B9||GSSE (IEC 61850 8-1)|
|0x88BA||Multicast sampled values (IEC 61850 8-1)|
|01-00-0C-CC-CC-CC||SNAP (length)||Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Unidirectional_Link_Detection (UDLD)|
|01-00-0C-CC-CC-CD||SNAP (length)||Cisco Shared Spanning Tree Protocol Address|
802.11 wireless networks use the same MAC addresses for multicast as Ethernet.
In network prefix or Classless Inter-Domain Routing ( CIDR) notation, IP multicast addresses are summarized as 18.104.22.168/4.
((cite book)): CS1 maint: multiple names: authors list (link)
Lacking anything better to call it, one of the authors [of RFC2770], David Meyer, simply began refer to this as "GLOP" addressing and the name stuck.
most Layer 2 switches flood all multicast traffic that falls within the MAC address range of 0x0100.5E00.00xx [...] to all ports on the switch even if IGMP Snooping is enabled. [...] There are several multicast group ranges besides the 22.214.171.124/24 that will map to the 0x0100.5E00.00xx MAC address range and hence also will be flooded by most Layer 2 switches.
((cite web)): External link in