|Going in order of cheapest and normally least reliable, to more expensive, and most reliable.
A bus topology uses a single backbone segment (length of cable) that all the hosts connect to directly. It is very small scale (2-10 computers) and is extremely cheap. Think of a string of christmas lights, if one goes down, the network goes down.
A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable. This is more stable than the bus topology. If one cable or NIC goes out, the network can still operate by going the other way around the circle.
A star topology connects all cables to a central point of concentration. This point is usually a hub or switch. This is much better than the ring because a switch makes its forwarding desisions (based on the MAC table*). The only point that can shutdown the whole network is the one switch. Unlike in the past two examples, if a node goes down, the network is either shutdown or changed.
An extended star topology uses the star topology to be created. It links individual stars together by linking the hubs/switches. Picture a snowflake, with branches going off from a central point. the branches are smaller star networks connected by one switch or router at the center. This is used for larger networks. Very stable exept that if one switch/router goes down, that section of the network goes down.
A mesh topology is used when there can be absolutely no break in communications. Picture a pentagon, and connect all the points of the pentagon to each other point. Each connecting line is a network connection to the other nodes. If one node/connection goes down, the other ones can still communicate via the other connections. In that example, it would take four down network connections to cutoff a node from the network. Very expensive, but near impossible to go "down." This also reflects the design of the Internet, which has multiple paths to any one location.
*I will be doing a class on CAIRC in the near future that will cover this and other Cisco CCNA related material.
This article was originally written by phantum415