Multicast address

Multicast address

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A multicast address is a logical identifier for a group of in a , that are available to process datagrams or frames intended for a designated network service. Multicast addressing can be used in the (Layer 2 in the model), such as multicast, and at the (Layer 3 for OSI) for Version 4 (IPv4) or Version 6 (IPv6) multicast.

Contents

[] IPv4

multicast addresses are defined by the leading address bits of 1110, originating from the design of the early Internet when this group of addresses was designated as Class D. The (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 , an (IETF) Best Current Practice document (BCP 51).

The following table is a partial list of well-known IPv4 addresses that are reserved for IP multicasting and that are registered with the (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 (DVMRP) to address multicast routers.
224.0.0.5	The (OSPF) AllSPFRouters address is used to send Hello packets to all OSPF routers on a network segment.
224.0.0.6	The OSPF AllDRouters address is used to send OSPF routing information to designated routers on a network segment.
224.0.0.9	The (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 (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.
224.0.0.13	(PIM) Version 2
224.0.0.18	(VRRP)
224.0.0.19 - 21	over IP
224.0.0.22	(IGMP) Version 3
224.0.0.102	(GLBP)
224.0.0.251	(mDNS) address
224.0.0.252	(LLMNR) address
224.0.1.1	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	discovery address

[] Local subnetwork

The address block 224.0.0.0/24 (224.0.0.0 to 224.0.0.255) is designated for multicasting on the local only. For example, the (RIPv2) uses 224.0.0.9, (OSPF) uses 224.0.0.5, and uses 224.0.0.251.

[] Source-specific multicast

The 232.0.0.0/8 block is reserved for use by .

[] GLOP addressing

The 233.0.0.0/8 range was originally assigned by as an experimental, public statically assigned multicast address space for publishers and Internet service providers, that wish to source content in the Internet. The allocation method is termed GLOP addressing and provides implementers a block of 255 addresses that is determined by their 16-bit number (ASN) allocation. In a nutshell, the middle two of this block are formed from assigned ASNs, allowing any operator assigned an ASN 256 globally unique multicast group addresses per ASN. The method is not applicable to the newer extension AS numbers which consist of 32 bits. , superseding , 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