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What’s a Network Topology

Network topology refers to the arrangement and interconnection of nodes within a network, typically documented through topology maps that serve as visual references for understanding and troubleshooting network infrastructure. These maps can represent physical connections, data flow, and logical routing across OSI layers 1, 2, and 3.

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About this video

Network topology is the study of how network nodes are arranged and interconnected, encompassing both the physical layout of devices and the logical paths through which data travels. Because networks can be complex and span multiple devices and segments, topology maps serve as essential reference documents that provide a visual representation of what actually exists within the environment. These maps make it possible to understand the structure of a network at a glance and form the foundation for effective network management and documentation. Topology maps are commonly organized around the OSI model, with separate or combined diagrams representing Layer 1 physical connections, Layer 2 data link relationships, and Layer 3 routing and logical network boundaries. A Layer 1 diagram might show how switches are physically cabled and stacked in a rack, while a Layer 2 map illustrates how data flows between those same devices, and a Layer 3 diagram focuses on routers and the subnets they connect. While additional detail such as port numbers or application data from higher OSI layers can be included, the lower three layers form the core of most network topology documentation. The practical value of topology maps becomes most apparent during troubleshooting. When connectivity issues arise, these diagrams allow network engineers to systematically trace a communication path, identify which devices are involved, and pinpoint exactly where a failure has occurred. Rather than investigating blindly, teams can reference the topology to determine whether traffic is reaching the first router, the second, or failing before either, dramatically reducing the time needed to isolate and resolve network problems.

What you'll learn

What's covered

Network Topology

Aligned to

CompTIA Network+
1.6 Compare and contrast network topologies, architectures, and types.
1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.
Cisco CCNA
1.2 Describe characteristics of network topology architectures
Cisco CCST Networking
1.1 Identify the fundamental conceptual building blocks of networks

Key terms

Network Topology
The arrangement and interconnection of network nodes, often represented as maps showing physical and logical connectivity.
Physical Layer
Layer 1 of the OSI model, responsible for the transmission of raw bits over a physical medium.
Data Link Layer
Layer 2 of the OSI model responsible for node-to-node data transfer and error detection on a single network segment.
Network Layer
Layer 3 of the OSI model, responsible for logical addressing and routing data packets between networks.
Open Systems Interconnection Model
OSI
A conceptual framework that standardizes network communication into seven distinct layers.
Switch
A network device that connects devices within a LAN and forwards traffic based on MAC addresses.
Router
A network device that forwards data packets between networks based on IP addresses.

Transcript

If we're going to be taking a look at different types of topology, let's make sure that we really understand what a topology is and what that looks like.

What a Topology Is

The word topology means how parts are interrelated or arranged. So when we're talking about network topology, we're talking about the arrangement and connection of network nodes and how we're interconnecting those.

We often associate network topologies with maps. Why? Because when we're connecting things, we're creating some sort of topology here, and by interconnecting them, what we want to do is have some sort of reference for that. So we create a map. This really helps with things like troubleshooting. When something goes awry and we need to figure out what's going on on our network and explore it, it helps to have some sort of reference for that. So we create network topology maps so that way we can see a representation of what actually exists. We use this map to see how our network is interconnected.

Different Maps for Different Layers

Many times we have many different maps that represent different aspects of the same network. Here's an example of it. Maybe we have a bunch of switches on a rack and need to understand how these switches are stacked on the rack physically and how they're physically connected. What we're talking about here is layer 1. From a layer 1 perspective, how do these switches interconnect? So we could have a map that outlines this physical connection.

Or maybe how data flows within the network. This is an example of how data might flow from layer 2 using those same switches. Or perhaps what we want to do is represent all of the layer three network within ours, so these are routers right here. This is representing the routers and the layer three devices on our network. And then rather than having switches on it, maybe we just have branches out here for our different LANs, and those represent different LANs there. So it could have different pieces of information on it.

There are times when we actually incorporate this layer 1, this layer 2 and layer 3, that we might incorporate multiple layers in the same map. Like maybe we have a network diagram that represents layer 2 and three, or maybe it represents one and two, or one and three, or one two and three. So there are different ways that we could actually lay this out on here.

Which Layers We Usually Show

Really, what we record on these diagrams could really vary and be at any of these layers. For instance, we could do ports for layer 4, or we could do the apps that we're using for layer 7. But generally speaking, when we're showing the topology, the interconnection, what we're really talking about is the layer 1, 2, and three: how physically it's connected, how the data link layer is connected, and how the network layer is connected. So usually we're representing the bottom layers of this, one, two, and three.

So if one device on here is not successfully talking to another device, we can start figuring out where is the disconnect. Can we make it to the first router, or maybe the second router, or third router? And if we find that one of these are down, we may find that is where the issue is at. So pulling out this map can help us troubleshoot and figure out where might there be issues.

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