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