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

ring

• 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

bus

• 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

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

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.

 

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