As explained in the chapter 1, IANA has reserved Class D range for multicast. The difference between the multicast and unicast address, is that unicast IP addresses represent a single network device while multicast represent a group of network devices or receivers.
The range of IP that is reserved for multicast is from 224.0.0.0 until 239.255.255.255. But how did we come with this range. For this, we need to look at the binary representation of the IP address:
As you can see, the first 4 bits from the first octet are 1110 in binary which means that we have multicast addresses from 224.0.0.0 until 239.255.255.255
However, it is important to mention that you cannot use all this range when you want to do multicast in your network. There are some ranges that are reserved such as the range 224.0.0.0 – 224.0.0.255 which is reserved by IANA. This range is used with network protocols. If you use this range for multicast, then it will not be forwarded by routers between subnets. Here below a list of reserved multicast addresses (you may have seen some of them before):
| 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 |
As you can see, the whole range is reserved by IANA and you may have recognized some of the multicast addresses such as 224.0.0.5 & 224.0.06 which are used for OSPF, 224.0.0.9 which is used in RIPv2 and so forth. So bottom line, do not use the range of 224.0.0.0/24 when you want to use multicast in your network.
Additionally, IANA also reserved the subnet of 224.0.1.0/24 to be used for certain applications. If you use this range, the router can route it unlike 224.0.0.0/24 range, however it is highly recommended to not use it because this is used for some applications such as:
| Address | Usage |
| 224.0.1.0 | VMTP Managers Group |
| 224.0.1.1 | NTP |
| 224.0.1.2 | SGI-Dogfight |
| 224.0.1.3 | Rwhod |
| 224.0.1.6 | NSS |
| 224.0.1.8 | SUN NIS+ |
| 224.0.1.20 | Any Private Experiment |
| 224.0.1.21 | DVMRP on MOSPF |
| 224.0.1.32 | Mtrace |
| 224.0.1.33 | RSVP-encap-1 |
| 224.0.1.34 | RSVP-encap-2 |
| 224.0.1.39 | Cisco-RP-Announce |
| 224.0.1.40 | Cisco-RP-Discovery |
| 224.0.1.52 | Mbone-VCR-Directory |
| 224.0.1.78 | Tibco Multicast 1 |
| 224.0.1.79 | Tibco Multicast 2 |
| 224.0.1.80 – 224.0.1.255 | Unassigned |
In summary, when you want to do multicast do not use the following 2 ranges:
- 0.0.0/24
- 0.1.0/24
The last thing that I want to mention about the multicast IP addressing is that as we do have unicast public and private IP addresses, we also have the same in multicast. IANA has reserved the subnet 239.0.0.0/8 to be used for multicast in our local networks, that means everything between 239.0.0.0 – 239.255.255.255 is safe to use in our networks for multicast.
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