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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 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]

Local subnetwork
Addresses in the range of 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Multicast DNS uses 224.0.0.251. Routers must not forward these messages outside the subnet from 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 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 224.0.1.1.
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.[2]: §6 
SDP/SAP block
Addresses in the reserved 224.2.0.0/16 range are not individually assigned by IANA. Fallen out of use [11]: §10  for security considerations, experimental Session Announcement Protocol [12] 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 232.0.0.0/8 (IPv4) and ff3x::/32 (IPv6) blocks are reserved for use by source-specific multicast.
GLOP[13]
The 233.0.0.0/8 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.[14] 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.[15] The method is not applicable to the newer 32-bit ASNs. In September 2001, the IETF envisioned a broader use of the range for many-to-many multicast applications.[16] Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.[citation needed]
Unicast-prefix-based
The 234.0.0.0/8 range is assigned as a range of global IPv4 multicast address space provided to each organization that has /24 or larger globally routed unicast address space allocated; one multicast address is reserved per /24 of unicast space.[17] A resulting advantage over GLOP is that the unicast-prefix mechanism resembles the unicast-prefix capabilities of IPv6.[18]
Administratively scoped
The 239.0.0.0/8 range is assigned for private use within an organization.[19] 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 239.0.0.0/8 range may be structured to be loosely similar to the scoped IPv6 multicast address.[20]
Ethernet-specific
In support of link-local multicasts which do not use IGMP, any IPv4 multicast address that falls within the *.0.0.0/24 and *.128.0.0/24 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.[21][dubious – discuss]

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).[5]

IPv6

Multicast addresses in IPv6 use the prefix ff00::/8.[20]

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;[20] the most-significant flag bit is reserved for future use.

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.

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.

Link-scoped multicast addresses use a comparable format.[27]

Based on the value of the flag bits, IPv6 multicast addresses can be Unicast-Prefix-based Multicast Addresses,[18] Source-Specific Multicast Addresses,[18] or Embedded RP IPv6 Multicast Addresses.[26] 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.

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.

Notable IPv6 multicast addresses

The following table is a list notable IPv6 multicast addresses that are registered with IANA.[29]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.[30] 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.[31]

Ethernet

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.[35]

802.11

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

See also

Notes

  1. ^ x is a place holder indicating that the value of the flags field is unimportant in the current discussion.
  2. ^ 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.

References

  1. ^ 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.
  2. ^ a b c d e M. Cotton; L. Vegoda; D. Meyer (March 2010). IANA Guidelines for IPv4 Multicast Address Assignments. IETF. doi:10.17487/RFC5771. ISSN 2070-1721. BCP 51. RFC 5771. Best Common Practice. Obsoletes RFC 3138 and 3171. Updates RFC 2780.
  3. ^ a b c IP Multicast Routing Configuration Guide, Cisco, retrieved 2021-01-13
  4. ^ AD-HOC Block 1
  5. ^ a b c d "IANA IP multicast addresses assignments". Internet Assigned Numbers Authority.
  6. ^ SDP/SAP Block
  7. ^ AD-HOC Block 2
  8. ^ Fall, K.R. and Stevens, W.R. (2011). TCP/IP Illustrated. Vol. 1. Addison-Wesley. p. 55. ISBN 9780321336316.{{cite book}}: CS1 maint: multiple names: authors list (link)
  9. ^ AD-HOC Block 3
  10. ^ Unicast-Prefix-based IPv4 Multicast Addresses
  11. ^ Begen, A; Kyzivat, P; Perkins, C; Handley, M (January 2021). SDP: Session Description Protocol. Internet Engineering Task Force (IETF). doi:10.17487/RFC8866. ISSN 2070-1721. RFC 8866. Proposed Standard. Obsoletes RFC 4566.
  12. ^ Handley, M; Perkins, C; Whelan, E (October 2000). Session Announcement Protocol. Network Working Group. doi:10.17487/RFC2974. RFC 2974. Experimental.
  13. ^ Joseph, Vinod; Mugulu, Srinivas (2011). Deploying Next Generation Multicast-Enabled Applications - Label Switched Multicast for MPLS, VPN, VPLS, and Wholesale Ethernet. Morgan Kaufmann/Elsevier. p. 7. ISBN 978-0-12-384923-6. 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.
  14. ^ D. Meyer; P. Lothberg (February 2000). GLOP Addressing in 233/8. Network Working Group. doi:10.17487/RFC2770. RFC 2770. Obsolete. Obsoleted by RFC 3180.
  15. ^ "Frequently Asked Questions (FAQ) File for Multicasting". Multicast Tech. Archived from the original on 2011-05-16.
  16. ^ D. Meyer; P. Lothberg (September 2001). GLOP Addressing in 233/8. Network Working Group. doi:10.17487/RFC3180. BCP 53. RFC 3180. Best Common Practice. Obsoletes RFC 2770.
  17. ^ M. Thaler (October 2010). Unicast-Prefix-Based IPv4 Multicast Addresses. Internet Engineering Task Force (IETF). doi:10.17487/RFC6034. ISSN 2070-1721. RFC 6034. Proposed Standard.
  18. ^ a b c d e B. Haberman; D. Thaler (August 2002). Unicast-Prefix-based IPv6 Multicast Addresses. Network Working Group. doi:10.17487/RFC3306. RFC 3306. Proposed Standard. Updated by RFC 3956, 4489 and 7371.
  19. ^ a b D. Meyer (July 1998). Administratively Scoped IP Multicast. Network Working Group. doi:10.17487/RFC2365. BCP 23. RFC 2365. Best Common Practice.
  20. ^ a b c d R. Hinden; S. Deering (February 2006). IP Version 6 Addressing Architecture. Network Working Group. doi:10.17487/RFC4291. RFC 4291. Draft Standard. Obsoletes RFC 3513. Updated by RFC 5952, 6052, 7136, 7346, 7371 and 8064.
  21. ^ "Guidelines for Enterprise IP Multicast Address Allocation" (PDF). Cisco. p. 7. Retrieved 2023-01-14. 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.
  22. ^ B. Cain; S. Deering; I. Kouvelas; B. Fenner; A. Thyagarajan (October 2002). Internet Group Management Protocol, Version 3. Network Working Group. doi:10.17487/RFC3376. RFC 3376. Proposed Standard. Updates RFC 2236. Updated by RFC 4604.
  23. ^ C. Huitema (February 2006). Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs). Network Working Group. doi:10.17487/RFC4380. RFC 4380. Proposed Standard. Updated by RFC 5991 and 6081.
  24. ^ "IPv4 Multicast Address Space Registry". www.iana.org. Retrieved 2024-06-30.
  25. ^ Silvia Hagen (May 2006). IPv6 Essentials (Second ed.). O'Reilly. ISBN 978-0-596-10058-2.
  26. ^ a b c P. Savola; B. Haberman (November 2004). Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address. Network Working Group. doi:10.17487/RFC3956. RFC 3956. Proposed Standard. Updated by RFC 7371. Updates RFC 3306.
  27. ^ J-S. Park; M-K. Shin; H-J. Kim (April 2006). A Method for Generating Link-Scoped IPv6 Multicast Addresses. Network Working Group. doi:10.17487/RFC4489. RFC 4489. Proposed Standard. Updates RFC 3306.
  28. ^ a b R. Droms (August 2014). IPv6 Multicast Address Scopes. Internet Engineering Task Force. doi:10.17487/RFC7346. ISSN 2070-1721. RFC 7346. Proposed Standard. Updates RFC 4007 and 4291.
  29. ^ "IPv6 Multicast Address Space Registry". Internet Assigned Numbers Authority.
  30. ^ P. Savola (January 2008). Overview of the Internet Multicast Routing Architecture. Network Working Group. doi:10.17487/RFC5110. RFC 5110. Informational.
  31. ^ S. Deering; W. Fenner; B. Haberman (October 1999). Multicast Listener Discovery (MLD) for IPv6. Network Working Group. doi:10.17487/RFC2710. RFC 2710. Proposed Standard. Updated by RFC 3590 and 3810.
  32. ^ R. Vida; L. Costa, eds. (June 2004). Multicast Listener Discovery Version 2 (MLDv2) for IPv6. Network Working Group. doi:10.17487/RFC3810. RFC 3810. Proposed Standard. Updates RFC 2710. Updated by RFC 4604.
  33. ^ a b T. Mrugalski; M. Siodelski; B. Volz; A. Yourtchenko; M. Richardson; S. Jiang; T. Lemon; T. Winters (November 2018). Dynamic Host Configuration Protocol for IPv6 (DHCPv6). IETF. doi:10.17487/RFC8415. ISSN 2070-1721. RFC 8415. Proposed Standard. Obsoletes RFC 3315, 3633, 3736, 4242, 7083, 7283 and 7550.
  34. ^ B. Aboba; D. Thaler; L. Esibov (January 2007). Link-Local Multicast Name Resolution (LLMNR). Network Working Group. doi:10.17487/RFC4795. RFC 4795. Informational.
  35. ^ IEEE. "Standard Group MAC Address: A Tutorial Guide" (PDF). IEEE Standards Association. pp. 2–3. Archived from the original (PDF) on 2022-10-09.
  36. ^ Patton, Michael A.; et al. "Multicast (including Broadcast) Addresses". cavebear.com. Karl Auerbach.
  37. ^ "Standard Group MAC Address - Public Listing". IEEE-SA. Retrieved 30 November 2022.
  38. ^ "IANA Multicast 48-bit MAC Addresses". IANA. Retrieved 31 January 2021.
  39. ^ S. Deering (August 1989). Host Extensions for IP Multicasting. Network Working Group. doi:10.17487/RFC1112. STD 5. RFC 1112. Internet Standard 5. Obsoletes RFC 988 and 1054. Updated by RFC 2236.
  40. ^ a b D. Eastlake III; J. Abley (October 2013). IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters. Internet Engineering Task Force (IETF). doi:10.17487/RFC7042. ISSN 2070-1721. BCP 141. RFC 7042. Best Common Practice. Obsoletes RFC 5342. Updates RFC 2153.
  41. ^ M. Crawford (December 1998). Transmission of IPv6 Packets over Ethernet Networks. Network Working Group. doi:10.17487/RFC2464. RFC 2464. Proposed Standard. Obsoletes RFC 1972.