IP Multicast the basics

IP Multicast is a seldom used but very useful mechanism for groups of machines to communicate. I will cover the basics of IP multicast in this document.

IP Multicast addresses

The typical IP addresses used by computers networking today are known as unicast addresses, meaning that every unicast address as a single (physical or logical) end point.

Most all computer networking is point to point between two specific IP addresses, you name it: web browsing, email exchange, transfer files and so much more.

However, there are other more specific forms on communication available and occasionally used: Broadcast and Multicast.

Broadcast vs. Multicast

  • Broadcast to everybody
  • Muilticast to a select group that have opted-in
  • Ethernet muilsticast addresses
  • Link local multicast and broadcast used all the time
  • Stays on a single physical link (or broadcast doamin if switches)
  • efficient transfer of redundant info
  • resource discovery

IP Multicast and IP mutlicast addresses

  • IP also has multicast address (class D) 224.0.0.0/32 to 239.255.255.25532
  • one sender many recievers

IP Multicast Routing

Setting up local IP multicast domains is not very difficult, IFF you have control over the local network, and can quickly recover if something goes wrong.

IP Multicast Routing Interdomain (worlwide!)

Multicast can extend beyond a link local network, building or company. But it is heavily regulated and global multicast feeds are generally not available unless you have a specific application and setup blessed by the powers above.

IP Multicast In the Real World

TODO: provide real world examles for this article.

TODO refer to my multicast work CRS and pimd