Multicast Address - FF00::/8

IP Multicast is a method of sending data to a group of hosts in a single transmission.  The principal idea behind multicast is to reduce duplicate datagrams that are being sent out from the same host to a group of indented recipients.  Imagine a host trying to send a message out to 50 other hosts.  Instead of connect to 50 hosts individually and send the message out, the host using IP Multicast would send the message to a special Multicast Address one time then those 50 hosts subscribe to that multicast address and would get the same message.  It's a huge bandwidth saver for the sending host.  Typically, IP Multicast is often employed in voice & video applications where bandwidth demand is high.

This technique of sending data is often referred to as a one-to-many communication as there is only one sending host and multiple receiving hosts.  The same IP Multicast Address is used for both the sending host & the receiving hosts.  Sending host would use it as the destination to send the message to while the receiving hosts use it to subscribe to or in other words, inform the network that they want to receive the message sent to that multicast address.

IPv6 Multicast Address has the prefix of FF00::/8 which are broken down into four groups as follows:

  • 8 bitsprefix
  • 4 bitsflags
  • 4 bitsscope
  • 112 bitsgroup ID
  • FF
  • 0
  • 2
  • AAAA:FEE5:0000:0000:0000:0001:0003

All 8 bits of the prefix are set o 1's.  The left most bit or the most significant bit of the Flags is reserved for future use while the next 3 bits are defined as RPT (Rendezvous, Prefix and Transient). 

Click on this link to examine the Multicast Address using the Advanced Online IPv6 Subnet Calculator: FF02:AAAA:FEE5:0000:0000:0000:0001:0003