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 184.108.40.206 through 220.127.116.11 range for IP multicast addresses.
Some of the addresses are reserved however and we can’t use them for our own applications.
The 18.104.22.168 – 22.214.171.124 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:
|126.96.36.199||All Multicast Routers|
|188.8.131.52||OSPF DR/BDR Router|
|184.108.40.206||DHCP Server / Relay|
|220.127.116.11||All PIM Routers|
|18.104.22.168||All CBT Routers|
|22.214.171.124 – 255||Unassigned|
You probably recognized OSPF (126.96.36.199 and 188.8.131.52), RIPv2 (184.108.40.206) and EIGRP (220.127.116.11). Once you dive more into multicast you will also encounter PIM (Protocol Independent Multicast) with 18.104.22.168.
IANA also reserved the 22.214.171.124 /24 range for certain applications. Everything in the 126.96.36.199 /24 range can be routed however, unlike the 188.8.131.52 /24 range. Here’s an overview: