📡 Enter IPv4 Multicast Address
Enter a valid IPv4 multicast address (224.0.0.0 – 239.255.255.255).
Must be in Class D range: 224.0.0.0 to 239.255.255.255
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Multicast MAC Address
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Sources & Methodology
Multicast address ranges from IANA IPv4 Multicast Address Space Registry. MAC mapping from RFC 1112. SSM range from RFC 4607. IGMPv3 from RFC 3376.
IANA IPv4 Multicast Address Space Registry
Authoritative registry of all assigned IPv4 multicast addresses and ranges. Source for well-known address assignments including OSPF, VRRP, HSRP, PIM, IGMP, mDNS, and all other protocol-specific multicast addresses.
RFC 1112 — Host Extensions for IP Multicasting
Defines the mapping of IPv4 multicast addresses to Ethernet multicast MAC addresses using the 01:00:5E prefix and the low-order 23 bits of the IP address.
RFC 4607 — Source-Specific Multicast for IP
Defines the SSM address range 232.0.0.0/8 for IPv4 Source-Specific Multicast. Source for SSM range classification and IGMPv3 requirement for SSM deployments.
Methodology — Multicast IP to MAC conversion (RFC 1112):
MAC = 01:00:5E : [IP octet 2 & 0x7F] : [IP octet 3] : [IP octet 4]
Start with IANA prefix 01:00:5E. Set the next bit to 0 (drops the MSB of the 2nd IP octet). Append the last 3 octets of the IP with the MSB of the second octet masked to 0. This uses only 23 of the 28 multicast group bits, causing 32 IP addresses to map to each MAC.
Last reviewed: April 2026
How Are IP Multicast Addresses Classified?
All IPv4 multicast addresses fall in the Class D range 224.0.0.0 to 239.255.255.255. This range is subdivided into distinct blocks, each serving a specific purpose. Understanding which block an address belongs to is critical for firewall configuration, PIM mode selection, IGMP version requirements, and multicast routing policy.
Multicast MAC = 01:00:5E:[last 23 bits of IP as 3 bytes]
Example: 224.1.2.3 to MAC
IP in binary: 11100000.00000001.00000010.00000011
Last 23 bits: 000 0000 0001 | 0000 0010 | 0000 0011
Hex: 00.01.02.03
Full MAC: 01:00:5E:01:02:03
Note: 225.1.2.3 maps to the SAME MAC (the upper 5 bits are lost)
IP in binary: 11100000.00000001.00000010.00000011
Last 23 bits: 000 0000 0001 | 0000 0010 | 0000 0011
Hex: 00.01.02.03
Full MAC: 01:00:5E:01:02:03
Note: 225.1.2.3 maps to the SAME MAC (the upper 5 bits are lost)
IPv4 Multicast Address Ranges
| Range | Name | Scope | Use Case |
|---|---|---|---|
| 224.0.0.0/24 | Local Network Control | Link-local (TTL=1) | Routing protocols, VRRP, HSRP |
| 224.0.1.0/24 | Internetwork Control | Global | NTP (224.0.1.1), WINS |
| 224.0.2.0 - 224.0.255.255 | AD-HOC (historical) | Global | Legacy assignments |
| 224.1.0.0 - 231.255.255.255 | Global Scope ASM | Global | Any-source multicast applications |
| 232.0.0.0/8 | Source-Specific (SSM) | Global | SSM, requires IGMPv3, no RP needed |
| 233.0.0.0/8 | GLOP Addressing | Global | AS-based multicast allocation (RFC 3180) |
| 234.0.0.0/8 | Unicast-Prefix-Based | Global | RFC 6034 unicast-prefix multicast |
| 235.0.0.0 - 238.255.255.255 | Reserved / IANA | - | Unassigned, not for use |
| 239.0.0.0/8 | Administratively Scoped | Org-local | Private multicast (RFC 2365) |
Well-Known Multicast Addresses
| Address | Name | Protocol |
|---|---|---|
| 224.0.0.1 | All Hosts | General multicast |
| 224.0.0.2 | All Routers | General multicast |
| 224.0.0.5 | All OSPF Routers | OSPFv2 |
| 224.0.0.6 | All OSPF DR/BDR | OSPFv2 |
| 224.0.0.9 | All RIP Routers | RIPv2 |
| 224.0.0.10 | All EIGRP Routers | EIGRP |
| 224.0.0.13 | All PIM Routers | PIM |
| 224.0.0.18 | VRRP | VRRP |
| 224.0.0.22 | IGMPv3 Report | IGMPv3 |
| 224.0.0.102 | HSRP v2 | HSRP |
| 224.0.0.251 | mDNS | Multicast DNS |
| 224.0.1.1 | NTP | Network Time Protocol |
💡 MAC ambiguity: Because only 23 of 28 multicast group bits are used in the Ethernet MAC mapping, 32 different multicast IP addresses map to the same MAC. For example, 224.1.1.1 and 225.1.1.1 both map to 01:00:5E:01:01:01. Hosts receive traffic for all 32 groups at the MAC layer and must filter at the IP layer, potentially causing unnecessary CPU overhead in dense multicast environments.
Frequently Asked Questions
IP multicast is a one-to-many communication method delivering a single packet to multiple receivers. IPv4 multicast uses the Class D range 224.0.0.0 to 239.255.255.255. This is divided into link-local (224.0.0.0/24), global ASM (224.0.1.0 to 231.255.255.255), SSM (232.0.0.0/8), and administratively scoped (239.0.0.0/8) ranges.
Start with IANA prefix 01:00:5E, then mask the second IP octet to 0 in the MSB position, and append the last 3 octets. Example: 224.1.2.3 becomes 01:00:5E:01:02:03. Only 23 of 28 multicast group bits are used, so 32 different IP multicast addresses map to the same MAC. Use the calculator above for instant conversion.
ASM (Any-Source Multicast) allows any source to send to a group. It uses PIM-SM with a Rendezvous Point and covers most of the multicast range. SSM (Source-Specific Multicast) uses 232.0.0.0/8 and allows receivers to specify the exact source IP, eliminating the need for an RP. SSM requires IGMPv3 and is simpler and more scalable for large deployments like IPTV.
The range 224.0.0.0/24 is link-local. These addresses have TTL=1 and are never forwarded by routers. Key assignments: 224.0.0.1 All Hosts, 224.0.0.2 All Routers, 224.0.0.5 OSPF All Routers, 224.0.0.6 OSPF DR/BDR, 224.0.0.9 RIP v2, 224.0.0.10 EIGRP, 224.0.0.13 PIM, 224.0.0.18 VRRP, 224.0.0.102 HSRP v2, 224.0.0.251 mDNS.
IGMP (Internet Group Management Protocol) manages multicast group membership. IGMPv1 (RFC 1112) provides basic join. IGMPv2 (RFC 2236) adds leave messages for faster departure. IGMPv3 (RFC 3376) adds source filtering for SSM, allowing hosts to specify which sources to receive. IGMPv3 is required for SSM (232.0.0.0/8 range). IGMPv2 is the most commonly deployed version for ASM.
The range 239.0.0.0/8 is reserved for administratively scoped multicast (RFC 2365). Analogous to RFC 1918 private addresses for multicast. These should never appear on the public internet. Sub-ranges: 239.255.0.0/16 is local scope, 239.254.0.0/16 is site-local scope. Use these ranges for internal multicast applications that must not cross organizational boundaries.
The Ethernet multicast MAC prefix 01:00:5E uses only 23 of the 28 available multicast group bits. The top 5 bits of the multicast group are discarded. This means 2^5 = 32 different multicast IP addresses share each MAC address. Hosts must filter unwanted traffic at the IP layer after receiving it at the MAC layer, potentially wasting CPU on dense multicast networks.
PIM (Protocol Independent Multicast) builds multicast distribution trees. PIM-SM (Sparse Mode) uses a Rendezvous Point for ASM. PIM-SSM supports the 232.0.0.0/8 range without an RP. PIM uses multicast address 224.0.0.13 for PIM Hello messages. The multicast address range determines which PIM mode applies: ASM ranges use PIM-SM, SSM range uses PIM-SSM.
Scope controls how far multicast traffic propagates. TTL 1 = link-local (not forwarded by routers), TTL 16 = site, TTL 64 = continental, TTL 128 = worldwide. Administratively scoped multicast (239.0.0.0/8) uses PIM boundaries instead of TTL for more reliable scope control. Modern networks prefer administrative boundary configuration over TTL-based scoping.
Key addresses to know: 224.0.0.1 All Hosts, 224.0.0.2 All Routers, 224.0.0.5 OSPF All Routers, 224.0.0.6 OSPF DR/BDR, 224.0.0.9 RIP v2, 224.0.0.10 EIGRP, 224.0.0.13 PIM, 224.0.0.18 VRRP, 224.0.0.22 IGMPv3, 224.0.0.102 HSRP v2, 224.0.0.251 mDNS, 224.0.1.1 NTP. Full registry at iana.org/assignments/multicast-addresses.
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