Managing Multicast in an Internetwork

Managing Multicast in an Internetwork
As a user on the network, you can understand that spam is not something that is managed by
a systems administrator, whereas valid mailing lists require maintenance to keep a current list
of valid subscribers. The same can be said of multicast. As we said earlier, one of the major differences
between broadcast and multicast communication is that broadcast traffic goes to all
hosts on a subnet, whereas multicast traffic goes only to the hosts that request it. The distinguishing
factor that puts multicast traffic so far ahead of broadcast traffic in utility is the ability
to specify which multiple hosts will receive the transmission.
This isn’t done magically; routers and switches don’t know who and where the recipients are
just because it’s multicast traffic. As with any application, protocols are needed to make things
happen. Multicast works on the basis of host subscription to groups.
Several methods and protocols have been developed and implemented to facilitate multicast
functionality within the internetwork:

Subscribing groups

Maintaining groups

Joining groups

Leaving groups
1 1 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1
01-00-5e-00-01-01
225.128.1.1
1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1
224.0.1.1
Final MAC
multicast address
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Chapter 19 
Understanding and Configuring Multicast Operation
Each of these protocols and methods is used for specific tasks or to achieve specific results
within the multicast environment. More importantly, each device in the network must know its
role regarding multicasting; otherwise, you are left with nothing except a broadcast.
We will now look at these protocols and learn just where they fit in and what they are needed
for. We begin with the most important—subscription and group maintenance—and then move
on to enhancements for multicast deployment and distribution.