Spanning Tree Again

http://www.cisco.com/image/gif/paws/10556/spanning_tree1.swf

Basic but well explained....

Multicast Again

Multicast communication is a one-to-many communication pattern. It can be viewed as a broadcast to a subset of nodes of the network

Source: http://upload.wikimedia.org/wikipedia/commons/7/7b/Multicast_forwarding.png