Multicast trivia

In multicast IP addressses, the low 28 bits are varied (the high four are a 1110). But in ethernet, only 23 bits are avaiable to multicast. So level 2 devices throw out the high 5 bits of the lower 28 of a multicast address, which obviously causes over-subscription on LANs. If you subscribe to 224.1.1.1, you'll get 224.129.1.1, 225.1.1.1, through 239.129.1.1.

Therefore! Kids, always vary the low byte of a multicast address.