Network Topologies

In networking, there are a number of different topologies that you will encounter. In this lesson, I’ll explain the most common topologies that are covered in the CCNA Routing & Switching exam(s).



Let’s start with the star topology…

Star Topology

You will see the star topology often when we talk about switches, here’s an example:

switch star topology hosts

It’s called a star topology because all communication has to go through the switch, it is the central component of our network.

Full Mesh

The full mesh topology means that each device is connected to all other devices. Here’s an example:

full mesh router topology

The advantage of a full mesh topology is that you have full redundancy. For example, in the picture above we can see routers in different cities. We can go from Los Angeles to New York with a direct connection. If this link fails, there are still plenty of backup links we can choose from. The downside of a full mesh topology is that it’s expensive. For each link, you will need to pay for the connection and you require additional interfaces on your routers.

Partial Mesh

An alternative to full mesh is the partial mesh topology. This is a trade-off between cost and redundancy. Here’s an example:

partial mesh router topology

The Los Angeles and New York sites are the most important ones, so they are connected to all other sites. There is no direct connection between San Francisco, Detroit and Miami. This doesn’t mean that these sites won’t be able to communicate with each other but communication has to go through the Los Angeles or New York sites.

You might also encounter partial mesh topologies on our LANs. For example:

partial mesh switch building topology

Above we see the switches in a single building. The access layer switches (A1 and A2) are connected to the distribution layer switches (D1 and D2) with partial mesh. There is no link in between the two access switches. The distribution layer switches however, are connected to each other and the two access layer switches (full mesh).

Hub and Spoke

Another topology we might encounter is the hub and spoke topology:

hub and spoke topology

In this topology, we have one central device called the hub and the other devices are called spokes. Above we see that the New York router is our hub, Miami and Los Angeles are two spoke routers. When our two spoke routers want to communicate with each other, it will have to go through the hub router.

Hybrid

In reality, we will mix a lot of the network topologies that we described above. Here’s an example of a complete network:

hybrid topology

Here’s what we see above:

  • Our LAN located in New York with two buildings and a core layer.
  • Each building has access and distribution layer switches. The access layer switches are connected with partial mesh to the distribution layer switches. The distribution layer switches use full mesh.
  • The buildings are connected with full mesh to two core layer switches.
  • Our WAN is connected to Los Angeles and Miami with full mesh.
  • Our WAN is also connected to Amsterdam and Paris, our New York router is the hub and Amsterdam/Paris are two spoke routers.

Conclusion

I hope these examples have been useful to understand the different network topologies that you might encounter. Keep in mind that in reality, we use a combination of these different topologies.


Forum Replies

  1. Hi guys.
    I was not able to find lessons about that.

    Can you explain the difference between a LAN SWITCH and a SAN SWITCH?

    Thank you very much

  2. Hello Giovanni

    The first thing we should do is determine the difference between a LAN and a SAN. A LAN is already well defined within the Introduction to LANs lesson. A SAN is a storage area network, which is a network architecture that is used to provide access to consolidated data storage. This is often used within a datacenter to provide servers with direct high-speed access to a shared storage repository.

    SANs can use conventional Layer 2 networking protocols such as Ethernet, but must often use a specialized Layer 3 protocol called Fiber Channel (FC) wh

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  3. Hello Pau

    Yes, you are correct. I believe that the point of the diagram was to show the various interconnections that can be made without actually showing every individual link. However, I will let Rene know to clarify and possibly to modify the image.

    Thanks again for pointing this out!

    Laz

  4. Hello Victor

    Yes, your suggestion is excellent. This would allow traffic between buildings to avoid going through the New York router, offloading a lot of work from that device. It would also provide a level of redundancy, in case one of the core routers failed (if you enable something like load-balanced routing, HSRP, Stacking, or VSS.

    You are correct again, that it would be beneficial to enable redundancy at the New York router, for both links, as well as in hardware. The NY router is a single point of failure that would cause a disconnection between multi

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  5. Hello Peter

    That’s a good question, and it is true that terminology can sometimes be confusing. The term hub is used in various situations, and its meaning must be identified based on the context.

    A Layer 2 hub is a device that physically looks like a switch, as shown below. It does the same thing as a switch, that is, it interconnects network devices by having them plug into the Ethernet ports, and allows them to communicate with each other.

    https://cdn-forum.networklessons.com/uploads/default/original/2X/8/842abbc01bfc51d8b3eb556189db3fb618ffd8d6.png

    The di

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