Multicast IP Addresses Overview

One of the differences between unicast and multicast IP addresses, is that unicast IP addresses represent a single network device while multicast IP addresses represent a group of receives. IANA has reserved the class D range to use for multicast. The first 4 bits in the first octet are 1110 in binary which means that we have the 224.0.0.0 through 239.255.255.255 range for IP multicast addresses.

multicast class D range

Some of the addresses are reserved however and we can’t use them for our own applications.

The 224.0.0.0 – 224.0.0.255 range has been reserved by IANA to use for network protocols. All multicast IP packets in this range are not forwarded by routers between subnets. Let me give you an overview of reserved link-local multicast addresses, I’m sure you recognize some of the protocols:

Address Usage
224.0.0.1 All Hosts
224.0.0.2 All Multicast Routers
224.0.0.3 Unassigned
224.0.0.4 DVMRP Routers
224.0.0.5 OSPF Routers
224.0.0.6 OSPF DR/BDR Router
224.0.0.7 ST Routers
224.0.0.8 ST Hosts
224.0.0.9 RIPv2 Routers
224.0.0.10 EIGRP Routers
224.0.0.11 Mobile Agents
224.0.0.12 DHCP Server / Relay
224.0.0.13 All PIM Routers
224.0.0.14 RSVP Encapsulation
224.0.0.15 All CBT Routers
224.0.0.16 Designated SBM
224.0.0.17 All SBMS
224.0.0.18 VRRP
224.0.0.19 – 255 Unassigned

You probably recognized OSPF (224.0.0.5 and 224.0.0.6), RIPv2 (224.0.0.9) and EIGRP (224.0.0.10).  Once you dive more into multicast you will also encounter PIM (Protocol Independent Multicast) with 224.0.0.13.

IANA also reserved the 224.0.1.0 /24 range for certain applications. Everything in the 224.0.1.0 /24 range can be routed however, unlike the 224.0.0.0 /24 range. Here’s an overview:

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Forum Replies

  1. Awesome post we’ve got here…

    But a couple of things that didn’t quite sync in my mind.

    First; When you mention that RIPv2 (224.0.0.9) and basically the range 224.0.0.0/24 is NOT routed between subnets, so my question is how RIPv2-aware routers advertise RIPv2 routes?

    Second; Can you give an example of a work with 239.0.0.0/8, cos I fear that if I applied it on a typical LAN (where I’m restricted to use only private IP addresses) that is connected to the Internet, it cause a conflict… Ain’t that right?

  2. Hi M. Bahwal,

    Multicast traffic in the 224.0.0.0/24 range is processed by routers but it won’t be “routed” to another subnet. Imagine a couple of routers connected to each other to a switch. They’ll use 224.0.0.9 to communicate with each on this segment. These routers won’t forward these multicast packets to other interfaces.

    What kind of multicast example are you looking for? There are many different configurations…

    Best Regards,

    Rene

  3. “The 224.0.0.0 – 224.0.0.255 range h…”
    I think multicast address range is 224.0.0.0-224.255.255.255

  4. Hi Navin,

    The 224.0.0.0 - 224.0.0.255 is a “special” range that IANA has assigned for certain applications, these addresses are not routed outside of the subnet. For example, RIPv2, OSPF, EIGRP, etc.

    Rene

     

  5. for 224 range : One such example could be “ospf hello” which is not a user traffic but traffic among routers and does not require to be routed.
    where-in for 239 range …it is a multicast user traffic . thats how IANA has separated both range for multicast…is that correct to say?

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