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 224.0.0.0/4. [1] The group includes the addresses from 224.0.0.0 to 239.255.255.255.
The address range is divided into blocks each assigned a specific purpose or behavior. [2]
IP multicast address range | Description | Routable |
---|---|---|
224.0.0.0 to 224.0.0.255 | Local subnetwork [3] | No |
224.0.1.0 to 224.0.1.255 | Internetwork control | Yes |
224.0.2.0 to 224.0.255.255 | AD-HOC block 1 [4] | Yes |
224.1.0.0 to 224.1.255.255 | Reserved [2] : §3 [5] | |
224.2.0.0 to 224.2.255.255 | SDP/SAP block [6] | Yes |
224.3.0.0 to 224.4.255.255 | AD-HOC block 2 [7] | Yes |
225.0.0.0 to 231.255.255.255 | Reserved [2] : §3 [5] | |
232.0.0.0 to 232.255.255.255 | Source-specific multicast [3] | Yes |
233.0.0.0 to 233.251.255.255 | GLOP addressing [8] | Yes |
233.252.0.0 to 233.255.255.255 | AD-HOC block 3 [9] | Yes |
234.0.0.0 to 234.255.255.255[ citation needed ] | Unicast-prefix-based | Yes |
235.0.0.0 to 238.255.255.255 | Reserved [2] : §3 [5] | |
239.0.0.0 to 239.255.255.255 | Administratively scoped [3] | 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). [5]
IP multicast address | Description | Routable |
---|---|---|
224.0.0.0 | Base address (reserved) | No |
224.0.0.1 | The All Hosts multicast group addresses all hosts on the same network segment. | No |
224.0.0.2 | The All Routers multicast group addresses all routers on the same network segment. | No |
224.0.0.4 | This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers. | 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. | 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. | 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. | 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. | No |
224.0.0.13 | Protocol Independent Multicast (PIM) Version 2 | No |
224.0.0.18 | Virtual Router Redundancy Protocol (VRRP) | No |
224.0.0.19–21 | IS-IS over IP | No |
224.0.0.22 | Internet Group Management Protocol (IGMP) version 3 [21] : §4.2.14 | No |
224.0.0.102 | Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP) | No |
224.0.0.107 | Precision Time Protocol (PTP) version 2 peer delay measurement messaging | No |
224.0.0.251 | Multicast DNS (mDNS) address | No |
224.0.0.252 | Link-local Multicast Name Resolution (LLMNR) address | No |
224.0.0.253 | Teredo tunneling client discovery address [22] : §2.17 | No |
224.0.1.1 | Network Time Protocol clients listen on this address for protocol messages when operating in multicast mode. | Yes |
224.0.1.22 | Service Location Protocol version 1 general | Yes |
224.0.1.35 | Service Location Protocol version 1 directory agent | Yes |
224.0.1.39 | The Cisco multicast router AUTO-RP-ANNOUNCE address is used by RP mapping agents to listen for candidate announcements. | 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. | Yes |
224.0.1.41 | H.323 Gatekeeper discovery address | Yes |
224.0.1.129–132 | Precision Time Protocol (PTP) version 1 messages (Sync, Announce, etc.) except peer delay measurement | Yes |
224.0.1.129 | Precision Time Protocol (PTP) version 2 messages (Sync, Announce, etc.) except peer delay measurement | Yes |
224.0.23.12 | KNXnet/IP discovery [23] | Yes |
239.255.255.250 | Simple Service Discovery Protocol address | Yes |
239.255.255.253 | Service Location Protocol version 2 address | Yes |
Multicast addresses in IPv6 use the prefix ff00::/8. [19]
bits | 8 | 4 | 4 | 112 |
---|---|---|---|---|
field | prefix | flg | sc | group ID |
For all multicast addresses, the prefix field holds the binary value 11111111.
Currently, three of the four flag bits in the flg field are defined; [19] the most-significant flag bit is reserved for future use.
bit | flag | Meaning when 0 | Meaning when 1 |
---|---|---|---|
8 | reserved | reserved | reserved |
9 | R (Rendezvous) [25] | Rendezvous point not embedded | Rendezvous point embedded |
10 | P (Prefix) [17] | Without prefix information | Address based on network prefix |
11 | T (Transient) [19] | Well-known multicast address | Dynamically assigned multicast address |
The four-bit scope field (sc) is used to indicate where the address is valid and unique.
In addition, the scope field is used to identify special multicast addresses, like solicited node.
bits | 8 | 4 | 4 | 79 | 9 | 24 |
---|---|---|---|---|---|---|
field | prefix | flg | sc | zeroes | ones | unicast address |
The sc(ope) field holds the binary value 0010 (link-local). Solicited-node multicast addresses are computed as a function of a node's unicast or anycast addresses. A solicited-node multicast address is created by copying the last 24 bits of a unicast or anycast address to the last 24 bits of the multicast address.
bits | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
---|---|---|---|---|---|---|---|---|
field | prefix | flg | sc | res | riid | plen | network prefix | group ID |
Link-scoped multicast addresses use a comparable format. [26]
Based on the value of the flag bits, IPv6 multicast addresses can be Unicast-Prefix-based Multicast Addresses, [17] Source-Specific Multicast Addresses, [17] or Embedded RP IPv6 Multicast Addresses. [25] 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.
IPv6 address [note 1] | IPv4 equivalent [18] : §8 | Scope [27] | 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 [27] | 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 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. [28] 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. [29] 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. [30]
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 [31] |
ff02::1:2 | All DHCPv6 servers and relay agents on the local network segment [32] |
ff02::1:3 | All LLMNR hosts on the local network segment [33] |
ff05::1:3 | All DHCPv6 servers on the local network site [32] |
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 frames with a value of 1 in the least-significant bit of the first octet [note 2] 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. [34]
Block | Ethernet multicast address | Ethertype | Usage |
---|---|---|---|
01-80-C2-00-00-00 | 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) | |
01-80-C2-00-00-03 | 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) | |
01-80-C2-00-00-30 through 01-80-C2-00-00-3F | 0x8902 | Ethernet CFM Protocol IEEE 802.1ag | |
01-1B-19 | 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 |
01-00-5E-00-00-00 through 01-00-5E-7F-FF-FF | 0x0800 | IPv4 Multicast: [38] Insert the low 23 bits of the multicast IPv4 address into the Ethernet address [39] : §2.1.1 | |
33-33-xx | 33-33-00-00-00-00 through 33-33-FF-FF-FF-FF | 0x86DD | IPv6 multicast: [40] The low 32 bits an Ethernet address for IPv6 multicast traffic are the low 32 bits of the multicast IPv6 address used. [39] : §2.3.1 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. |
01-0C-CD | 01-0C-CD-01-00-00 through 01-0C-CD-01-01-FF | 0x88B8 | IEC 61850-8-1 GOOSE Type 1/1A |
01-0C-CD-02-00-00 through 01-0C-CD-02-01-FF | 0x88B9 | GSSE (IEC 61850 8-1) | |
01-0C-CD-04-00-00 through 01-0C-CD-04-01-FF | 0x88BA | Multicast sampled values (IEC 61850 8-1) | |
01-00-0C | 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[ citation needed ] |
802.11 wireless networks use the same MAC addresses for multicast as Ethernet.
An Internet Protocol address is a numerical label such as 192.0.2.1 that is assigned to a device connected to a computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface identification, and location addressing.
Internet Protocol version 4 (IPv4) is the first version of the Internet Protocol (IP) as a standalone specification. It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version deployed for production on SATNET in 1982 and on the ARPANET in January 1983. It is still used to route most Internet traffic today, even with the ongoing deployment of Internet Protocol version 6 (IPv6), its successor.
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion, and was intended to replace IPv4. In December 1998, IPv6 became a Draft Standard for the IETF, which subsequently ratified it as an Internet Standard on 14 July 2017.
Classless Inter-Domain Routing is a method for allocating IP addresses for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet. Its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.
Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS).
A subnetwork, or subnet, is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.
A classful network is an obsolete network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing (CIDR) in 1993. The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits. Classes A, B, and C provide unicast addresses for networks of three different network sizes. Class D is for multicast networking and the class E address range is reserved for future or experimental purposes.
A broadcast address is a network address used to transmit to all devices connected to a multiple-access communications network. A message sent to a broadcast address may be received by all network-attached hosts.
In Internet networking, a private network is a computer network that uses a private address space of IP addresses. These addresses are commonly used for local area networks (LANs) in residential, office, and enterprise environments. Both the IPv4 and the IPv6 specifications define private IP address ranges.
The Neighbor Discovery Protocol (NDP), or simply Neighbor Discovery (ND), is a protocol of the Internet protocol suite used with Internet Protocol Version 6 (IPv6). It operates at the internet layer of the Internet model, and is responsible for gathering various information required for network communication, including the configuration of local connections and the domain name servers and gateways.
In computer networking, the multicast DNS (mDNS) protocol resolves hostnames to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, packet formats and operating semantics as unicast Domain Name System (DNS). It was designed to work as either a stand-alone protocol or compatible with standard DNS servers. It uses IP multicast User Datagram Protocol (UDP) packets and is implemented by the Apple Bonjour and open-source Avahi software packages, included in most Linux distributions. Although the Windows 10 implementation was limited to discovering networked printers, subsequent releases resolved hostnames as well. mDNS can work in conjunction with DNS Service Discovery (DNS-SD), a companion zero-configuration networking technique specified separately in RFC 6763.
IP multicast is a method of sending Internet Protocol (IP) datagrams to a group of interested receivers in a single transmission. It is the IP-specific form of multicast and is used for streaming media and other network applications. It uses specially reserved multicast address blocks in IPv4 and IPv6.
In the Internet addressing architecture, the Internet Engineering Task Force (IETF) and the Internet Assigned Numbers Authority (IANA) have reserved various Internet Protocol (IP) addresses for special purposes.
Internet Control Message Protocol version 6 (ICMPv6) is the implementation of the Internet Control Message Protocol (ICMP) for Internet Protocol version 6 (IPv6). ICMPv6 is an integral part of IPv6 and performs error reporting and diagnostic functions.
In computer networking, a link-local address is a network address that is valid only for communications on a local link, i.e. within a subnetwork that a host is connected to. Link-local addresses are most often unicast network addresses assigned automatically through a process known as stateless address autoconfiguration (SLAAC) or link-local address autoconfiguration, also known as automatic private IP addressing (APIPA) or auto-IP. Link-local addresses are not all unicast; e.g. IPv6 addresses beginning with ff02:, and IPv4 addresses beginning with 224.0.0. are multicast addresses that are link-local.
A unique local address (ULA) is an Internet Protocol version 6 (IPv6) address in the address range fc00::/7. These addresses are non-globally reachable. For this reason, ULAs are somewhat analogous to IPv4 private network addressing, but with significant differences. Unique local addresses may be used freely, without centralized registration, inside a single site or organization or spanning a limited number of sites or organizations.
An Internet Protocol version 6 address is a numeric label that is used to identify and locate a network interface of a computer or a network node participating in a computer network using IPv6. IP addresses are included in the packet header to indicate the source and the destination of each packet. The IP address of the destination is used to make decisions about routing IP packets to other networks.
An IPv6 packet is the smallest message entity exchanged using Internet Protocol version 6 (IPv6). Packets consist of control information for addressing and routing and a payload of user data. The control information in IPv6 packets is subdivided into a mandatory fixed header and optional extension headers. The payload of an IPv6 packet is typically a datagram or segment of the higher-level transport layer protocol, but may be data for an internet layer or link layer instead.
A solicited-node multicast address is an IPv6 multicast address used by the Neighbor Discovery Protocol to determine the link layer address associated with a given IPv6 address, which is also used to check if an address is already being used by the local-link or not, through a process called DAD. The solicited-node multicast addresses are generated from the host's IPv6 unicast or anycast address, and each interface must have a solicited-node multicast address associated with it.
In network prefix or Classless Inter-Domain Routing ( CIDR) notation, IP multicast addresses are summarized as 224.0.0.0/4.
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: 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 224.0.0.0/24 that will map to the 0x0100.5E00.00xx MAC address range and hence also will be flooded by most Layer 2 switches.