Unicast-prefix-based 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 one multicast address is reserved per / 24 of unicast space. Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters. RFC 3180, superseding RFC 2770, envisioned the use of the range for many-to-many multicast applications. The method is not applicable to the newer 32-bit ASNs. 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. 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. GLOP 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. Source-specific multicast The 232.0.0.0 / 8 (IPv4) and ff3x:: / 32 (IPv6) blocks are reserved for use by source-specific multicast. These addresses are globally routed and are used for applications that don't fit either of the previously described purposes. AD-HOC block Addresses in three separate blocks are not individually assigned by IANA. 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. 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. Routers must not forward these messages outside the subnet from which they originate. 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. The address range is divided into blocks each assigned a specific purpose or behavior.Ģ34.0.0.0 to 234.255.255.255 Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) Best Current Practice document (BCP 51). The CIDR notation for this group is 224.0.0.0 / 4. This originates from the classful network design of the early Internet when this group of addresses was designated as Class D. You can only recover the last 23 bits of the IPv4 multicast address from the 48-bit MAC multicast address.IPv4 multicast addresses are defined by the most-significant bit pattern of 1110. The reverse mapping is more complex, and it is inexact since each 48-bit MAC multicast address actually represents 32 different IPv4 multicast addresses. That creates the 48-bit MAC multicast address from an IPv4 multicast address. Just take the 48-bit MAC multicast OUI of 01-00-5E, append a zero bit, and append the low-order 23 bits of the IPv4 multicast address. The mapping from an IPv4 multicast address to a 48-bit MAC multicast address is pretty simple. Each 48-bit MAC multicast address will map to 32 different IPv4 multicast addresses. That means there are 32 times ( 28-23=5 and 2^5=32) as many IPv4 multicast addresses as there are 48-bit MAC multicast addresses. You must somehow map the 28 bits of IPv4 addressing into 23 bits of MAC addressing.

The guy experimenting with multicast couldn't afford it, so he went in with someone else to buy the OUI, and they split it, each getting 23 bits of addressing in the OUI.Īn IPv4 multicast address has 28 bits of addressing ( 224.0.0.0/4, so 32-4=28). To get a 48-bit MAC address OUI (24 bits, leaving 24 bits for individual addresses) registered with the IEEE used to cost $1000, which was a lot of money in those days. To convert an IP multicast address to a 48-bit MAC multicast address you need to understand how the 48-bit MAC multicast address came about.

Multicast to mac address converter