Multicast address
Encyclopedia
A multicast address is a logical identifier for a group of host
s 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.
multicast addresses are defined by the leading address bits of 1110, originating from the classful network
design of the early Internet when this group of addresses was designated as Class D. The Classless Inter-Domain Routing
(CIDR) prefix of this group is
(IETF) Best Current Practice document (BCP 51).
The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicast
ing and that are registered with the Internet Assigned Numbers Authority
(IANA).
only. For example, the Routing Information Protocol
(RIPv2) uses 224.0.0.9, Open Shortest Path First
(OSPF) uses 224.0.0.5 & 224.0.0.6, and Zeroconf mDNS
uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate.
.
number (ASN) allocation. In a nutshell, the middle two octet
s 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 extension AS numbers. RFC 3180, superseding RFC 2770, envisioned the use of the range for many-to-many multicast applications. This block has been one of the most successful multicast addressing schemes. Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.
The administratively scoped address block is further subdivided.
Within each scope, the top 256 addresses are reserved for relative assignments. For example, the topmost relative assignment address is used by the Session Announcement Protocol
.
have the prefix ff00::/8. IPv6 multicast addresses are generally formed from four bit groups, illustrated as follows:
The prefix holds the binary value 11111111 for any multicast address.
Currently, 3 of the 4 flag bits in the flgs field are defined; the most-significant flag bit is reserved for future use. The other three flags are known as R, P and T.
Similar to unicast
addresses, the prefix of IPv6 multicast addresses specifies their scope, however, the set of possible scopes is different. The 4-bit sc (or scope) field (bits 12 to 15) is used to indicate where the address is valid and unique.
The service is identified in the 112-bit 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 partial list of well-known IPv6 multicast addresses that are registered with the Internet Assigned Numbers Authority
(IANA).
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
s in a computer network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
, that are available to process datagrams or frames intended to be multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
for a designated network service
Network service
Network services are the foundation of a networked computing environment. Generally network services are installed on one or more servers to provide shared resources to client computers.- Network services in LAN :...
. Multicast addressing can be used in the Link Layer
Link Layer
In computer networking, the link layer is the lowest layer in the Internet Protocol Suite , the networking architecture of the Internet . It is the group of methods or protocols that only operate on a host's link...
(Layer 2 in the OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
), such as Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
multicast, and at the Internet Layer
Internet layer
The internet layer or IP layer is a group of internetworking methods in the Internet protocol suite, commonly also called TCP/IP, which is the foundation of the Internet...
(Layer 3 for OSI) for Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
Version 4 (IPv4) or Version 6 (IPv6) multicast.
IPv4
IPv4IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
multicast addresses are defined by the leading address bits of 1110, originating from the classful network
Classful network
A classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the address space for Internet Protocol Version 4 into five address classes. Each class, coded in the first four bits of the...
design of the early Internet when this group of addresses was designated as Class D. The Classless Inter-Domain Routing
Classless Inter-Domain Routing
Classless Inter-Domain Routing is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet...
(CIDR) prefix of this group is
224.0.0.0/4. The group includes the addresses from 224.0.0.0 to 239.255.255.255. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task ForceInternet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...
(IETF) Best Current Practice document (BCP 51).
The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicast
IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...
ing and that are registered with the Internet Assigned Numbers Authority
Internet Assigned Numbers Authority
The Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...
(IANA).
| IP multicast address | Description |
|---|---|
| 224.0.0.0 | Base address (reserved) |
| 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 Distance Vector Multicast Routing Protocol The Distance Vector Multicast Routing Protocol , defined in RFC 1075, is used to share information between routers to facilitate the transportation of IP Multicast packets among networks... (DVMRP) to address multicast routers. |
| 224.0.0.5 | The Open Shortest Path First Open Shortest Path First Open Shortest Path First is an adaptive routing protocol for Internet Protocol networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system . It is defined as OSPF Version 2 in RFC 2328 for IPv4... (OSPF) 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 D Routers address is used to send OSPF routing information to designated routers on a network segment. |
| 224.0.0.9 | The Routing Information Protocol Routing Information Protocol The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15.... (RIP) 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 Enhanced Interior Gateway Routing Protocol Enhanced Interior Gateway Routing Protocol - is a Cisco proprietary routing protocol loosely based on their original IGRP. EIGRP is an advanced distance-vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of... (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment. |
| 224.0.0.13 | Protocol Independent Multicast Protocol Independent Multicast Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet... (PIM) Version 2 |
| 224.0.0.18 | Virtual Router Redundancy Protocol Virtual Router Redundancy Protocol The Virtual Router Redundancy Protocol is a computer networking protocol that provides for automatic assignment of available Internet Protocol routers to participating hosts... (VRRP) |
| 224.0.0.19 - 21 | IS-IS IS-IS Intermediate System To Intermediate System , is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices.... over IP |
| 224.0.0.22 | Internet Group Management Protocol Internet Group Management Protocol The Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships.... (IGMP) Version 3 |
| 224.0.0.102 | Hot Standby Router Protocol Hot Standby Router Protocol Hot Standby Router Protocol is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway, and has been described in detail in RFC 2281.... version 2 (HSRPv2) / Gateway Load Balancing Protocol Gateway Load Balancing Protocol Gateway Load Balancing Protocol is a Cisco proprietary protocol that attempts to overcome the limitations of existing redundant router protocols by adding basic load balancing functionality.... (GLBP) |
| 224.0.0.107 | Precision Time Protocol Precision Time Protocol The Precision Time Protocol is a protocol used to synchronize clocks throughout a computer network. On a local area network it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.... version 2 peer delay measurement messaging |
| 224.0.0.251 | Multicast DNS Multicast DNS Multicast DNS is a way of using familiar DNS programming interfaces, packet formats and operating , in a small network where no conventional DNS server has been installed.... (mDNS) address |
| 224.0.0.252 | Link-local Multicast Name Resolution Link-local Multicast Name Resolution The Link Local Multicast Name Resolution is a protocol based on the Domain Name System packet format that allows both IPv4 and IPv6 hosts to perform name resolution for hosts on the same local link... (LLMNR) address |
| 224.0.1.1 | Network Time Protocol Network Time Protocol The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L... clients listen on this address for protocol messages when operating in multicast mode. |
| 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 H.323 Gatekeeper An H.323 Gatekeeper serves the purpose of Call Admission Control and translation services from E.164 IDs to IP addresses in an H.323 telephony network. Gatekeepers can be combined with a gateway function to proxy H.323 calls and are sometimes referred to as Session Border Controllers... discovery address |
| 224.0.1.129 - 132 | Precision Time Protocol Precision Time Protocol The Precision Time Protocol is a protocol used to synchronize clocks throughout a computer network. On a local area network it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.... version 1 time announcements |
| 224.0.1.129 | Precision Time Protocol Precision Time Protocol The Precision Time Protocol is a protocol used to synchronize clocks throughout a computer network. On a local area network it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.... version 2 time announcements |
Local subnetwork
Addresses in the range 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetworkSubnetwork
A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....
only. For example, the Routing Information Protocol
Routing Information Protocol
The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15....
(RIPv2) uses 224.0.0.9, Open Shortest Path First
Open Shortest Path First
Open Shortest Path First is an adaptive routing protocol for Internet Protocol networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system . It is defined as OSPF Version 2 in RFC 2328 for IPv4...
(OSPF) uses 224.0.0.5 & 224.0.0.6, and Zeroconf mDNS
Zeroconf
Zero configuration networking , is a set of techniques that automatically creates a usable Internet Protocol network without manual operator intervention or special configuration servers....
uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate.
Internetwork control block
Addresses in the range 224.0.1.0 to 224.0.1.255 are individually assigned by IANA and designated the Internetwork Control Block. It is used for traffic that must be routed through the public Internet, such as for applications of the Network Time Protocol (224.0.1.1).AD-HOC block
Addresses in the ranges 224.0.2.0 to 224.0.255.255, 224.3.0.0 to 224.4.255.255 and 233.252.0.0 to 233.255.255.255 are individually assigned by IANA and designated the AD-HOC block. These addresses are globally routed and are used for applications that don't fit either of the previously described purposes.Source-specific multicast
The 232.0.0.0/8 block is reserved for use by source-specific multicastSource-specific multicast
Source-specific multicast is a method of delivering multicast packets in which the only packets that are delivered to a receiver are those originating from a specific source address requested by the receiver...
.
GLOP addressing
The 233.0.0.0/8 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 systemAutonomous system (Internet)
Within the Internet, an Autonomous System is a collection of connected Internet Protocol routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet....
number (ASN) allocation. In a nutshell, the middle two octet
Octet (computing)
An octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as there is no standard for the size of the byte.-Overview:...
s 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 extension AS numbers. RFC 3180, superseding RFC 2770, envisioned the use of the range for many-to-many multicast applications. This block has been one of the most successful multicast addressing schemes. Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.
Unicast-Prefix-Based IPv4 Multicast addresses
The 234.0.0.0/8 range is assigned by RFC 6034 as a range of global IPv4 multicast address space provided to each organization that has /24 or larger globally routed unicast address space allocated. A resulting advantage over GLOP is that the mechanisms in IPv4 and IPv6 become more similar.Administratively scoped addresses
The 239.0.0.0/8 range is assigned by RFC 2365 as a locally administered address space with local or organizational scope. It may be used by anyone, without concern for address collisions, for private multicast domains.The administratively scoped address block is further subdivided.
- 239.255.0.0/16 is designated for local scope. Any scope boundary is a boundary for local scope. Local scope address space may be extended downwards if necessary (i.e. to 239.254.0.0/16, 239.253.0.0/16, etc.).
- 239.192.0.0/14 is designated for organizational local scope. This space may be extended to 239.0.0.0/10, 239.64.0.0/10 and 239.128.0.0/10 if necessary.
Within each scope, the top 256 addresses are reserved for relative assignments. For example, the topmost relative assignment address is used by the Session Announcement Protocol
Session Announcement Protocol
Session Announcement Protocol is a protocol for broadcasting multicast session information.A SAP listening application can listen to the SAP multicast IP address and construct a guide of all advertised multicast sessions...
.
IPv6
Multicast addresses in IPv6IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
have the prefix ff00::/8. IPv6 multicast addresses are generally formed from four bit groups, illustrated as follows:
| Bits | 8 | 4 | 4 | 112 |
|---|---|---|---|---|
| Field | prefix | flgs | sc | group ID |
The prefix holds the binary value 11111111 for any multicast address.
Currently, 3 of the 4 flag bits in the flgs field are defined; the most-significant flag bit is reserved for future use. The other three flags are known as R, P and T.
| Flag | 0 | 1 |
|---|---|---|
| R (Rendezvous) | Rendezvous point not embedded | Rendezvous point embedded |
| P (Prefix) | Without prefix information | Address based on network prefix |
| T (Transient) | Well-known multicast address | Dynamically assigned multicast address |
Similar to unicast
Unicast
right|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
addresses, the prefix of IPv6 multicast addresses specifies their scope, however, the set of possible scopes 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 addressx is a place holder indicating that the value of the flags field is unimportant in the current discussion. | IPv4 equivalent | Scope | Purpose |
|---|---|---|---|
| ff00::/16-ff0f::/16 | Reserved | ||
| ffx1::/16 | 127.0.0.0/8 | 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 | IPv4 local scope | |
| 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 112-bit Group ID field. For example, if ff02::101 refers to all Network Time Protocol
Network Time Protocol
The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L...
(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 partial list of well-known IPv6 multicast addresses that are registered with the Internet Assigned Numbers Authority
Internet Assigned Numbers Authority
The Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...
(IANA).
| Address | Description |
|---|---|
| ff02::1 | All nodes on the local network segment |
| ff02::2 | All routers on the local network segment |
| ff02::5 | OSPFv3 AllSPF routers |
| ff02::6 | OSPFv3 AllDR routers |
| ff02::9 | RIP Routing Information Protocol The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15.... routers |
| ff02::a | EIGRP routers |
| ff02::d | PIM Protocol Independent Multicast Protocol-Independent Multicast is a family of multicast routing protocols for Internet Protocol networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet... routers |
| ff02::16 | MLDv2 Multicast Listener Discovery Multicast Listener Discovery is a component of the Internet Protocol Version 6 suite. MLD is used by IPv6 routers for discovering multicast listeners on a directly attached link, much like IGMP is used in IPv4. The protocol is embedded in ICMPv6 instead of using a separate protocol. MLDv1 is... reports (defined in RFC 3810) |
| ff02::1:2 | All DHCP servers and relay agents on the local network site (defined in RFC 3315) |
| ff05::1:3 | All DHCP servers on the local network site (defined in RFC 3315) |
| ff0x::fb | Multicast DNS |
| ff0x::101 | Network Time Protocol Network Time Protocol The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L... |
| ff0x::108 | Network Information Service Network Information Service The Network Information Service, or NIS is a client–server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network... |
| ff0x::114 | Used for experiments |
Ethernet
Ethernet frames with a value of 1 in the least-significant bit of the first octetOn 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. of the destination 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 network equipment 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.| Ethernet multicast address | Type Field | Usage |
|---|---|---|
| 01-00-0C-CC-CC-CC | 0x0802 | CDP Cisco Discovery Protocol The Cisco Discovery Protocol is a proprietary Data Link Layer network protocol developed by Cisco Systems. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address... (Cisco Discovery Protocol), VTP (VLAN Trunking Protocol) |
| 01-00-0C-CC-CC-CD | 0x0802 | Cisco Shared Spanning Tree Protocol Address |
| 01-80-C2-00-00-00 | 0x0802 | Spanning Tree Protocol (for bridges) IEEE 802.1D IEEE 802.1D 802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree and others. It is standardized by the IEEE 802.1 working group. It includes details specific to linking many of the other 802 projects including the widely deployed 802.3 , 802.11 and 802.16 standards.VLANs are not... |
| 01-80-C2-00-00-08 | 0x0802 | Spanning Tree Protocol (for provider bridges) IEEE 802.1AD |
| 01-80-C2-00-00-02 | 0x8809 | Ethernet OAM Protocol IEEE 802.3ah |
| 01-00-5E-xx-xx-xx | 0x0800 | IPv4 Multicast (RFC 1112) |
| 33-33-xx-xx-xx-xx | 0x86DD | IPv6 Multicast (RFC 2464) |