Network Topologies

Things I’ve never heard as a network security engineer:

“I see this network uses a star topology.”

“In order better understand your network, can you please let me know if you use a ring, star, bus, or mesh topology?”

Nobody talks about network topologies like it is explained in the books.

It is more common to just look at a network topology diagram.

Network Topology Diagrams A handy tool for network security engineers is a graphical representation of all the inter-connected devices that comprise a network, known as a network topology diagram. It can point out the locations of routers, firewalls, IPS devices, or database servers. It can additionally include all IP addresses and their associated subnets.

Study Notes
A network topology diagram is also a form of documentation. A crucial CISSP concept to understand is the importance of documentation in the security field.

The CISSP exam does not require you to study network diagrams to answer a question, but it does need you to know the basic concepts of network topologies.

There are 4 different types of network topologies that you need to know for the CISSP exam: ring, bus, star, mesh.

These topology concepts are a high-level overview of a bus, ring, and mesh topology.  

Then finally the star topology – perhaps the most common topology used today.

Ring Topology


• Every node has the ability to look at every packet passed around the cable
• A single break in the cable means the network is down
• If one device in the cable loop stops working, the network is down
• Since every device between the source and destination receives the packet – it makes for a slow network
• All devices have equal access to the cable

Bus Topology


• It is a simple network setup that is cost-efficient (it’s cheap to setup!)
• It’s good for a small local area network
• Not a great setup for security as every computer has the ability to see packets from every other computer
• If the single line of cable breaks, the network is down
• The ends of the single line of cable must have a terminator so that there isn’t a signal loop

Star Topology


You might not know it, but odds are good that the company that you work for is currently using a star topology for their network design. Your office computer plugs into an Ethernet port in the wall, which then plugs into a switch somewhere in a closet, which in turn plugs into a router that enables you access to the Internet.
It is called a star topology because all devices connect to a central device, and kind of makes a star shape as pictured in Figure 3 above. It is the most common network topology because if one node fails, it doesn’t affect the whole network.
Why is it the most common network topology?
• Unlike the ring topology, if one device goes down, the network does not go down
• But, if the central device (switch or hub) fails, then the nodes attached to that device are not able to communicate

Mesh Topology


If you want redundancy, the mesh topology is the best design around.  If you want a cabling nightmare, then the mesh topology is the best design around.  It isn’t a common network setup, you can find it in backbone networks.  Additionally, node traffic can be diverted to elsewhere if one node fails.