An IPv6 multicast address is an identifier for a group of interfaces (typically on different nodes). An interface may belong to any number of multicast groups. If the data is sent to this address, it has to be delivered to all interfaces in the multicast group. The distribution of video and audio signals in real time (videoconferences, radio and television broadcasting, etc.) is a typical example of the use of multicast addresses.
The prefix of each multicast address starts with the value FF in hexadecimal system (binary 11111111). Therefore, these addresses are easily recognizable. Multicast addresses have the following format:
Description of individual fields of multicast address:
Multicast address must never be used as a source address of the sender in an IPv6 datagram and it must not also be included in the Routing header.
The topic related to the multicast addresses is extensive. Therefore, we only discuss the individual types of multicast addresses. These are:
There are a number of multicast addresses with a special significance. These addresses are defined in RFC 4291. Pre-Defined Multicast addresses essentially replace the broadcast addresses. There are:
Pre-Defined Multicast addresses are used for some internal IPv6 mechanisms.
RFC 2375 defines other multicast groups that are used for various network protocols and services. For example, the multicast addresses FF0x::101 are used for NTP (Network Time Protocol).