TechKnowSurge
CompTIA Network+ 3.1 Cisco CCNA 1.2 Cisco CCST Networking 4.2 CompTIA Network+ 1.6
TechKnowSurge Catalog Videos Physical and Logical Diagrams
VideoNetworkFree

Physical and Logical Diagrams

Network diagrams come in two types—physical and logical—each representing a different aspect of how a network is structured and how data moves through it. Understanding both is essential for accurate documentation and effective troubleshooting.

⚑ Complete this video to capture a CTF flag worth 1 point.

About this video

Network documentation relies on two fundamentally different types of diagrams: physical and logical. A physical diagram represents the actual hardware connections—how devices like switches, routers, and endpoints are physically linked across buildings, floors, or campuses. A logical diagram represents how data flows and how devices are grouped into networks, which may bear little resemblance to the physical layout. Both views are necessary because each answers different questions and supports different aspects of network management and troubleshooting. The distinction becomes especially clear in environments that use VLANs. Physically, devices may share the same switches and cabling infrastructure, but logically they belong to entirely separate networks—such as administration, operations, or sales—and cannot communicate across those boundaries. A physical diagram alone would not reveal this segmentation, and a logical diagram alone would not show where cables run or where hardware is installed. Maintaining both types of diagrams gives network administrators a complete picture of their environment and a reliable reference when issues arise.

What you'll learn

Aligned to

CompTIA Network+
3.1 Explain the purpose of organizational processes and procedures.
1.6 Compare and contrast network topologies, architectures, and types.
Cisco CCNA
1.2 Describe characteristics of network topology architectures
Cisco CCST Networking
4.2 Use a network diagram to attach the appropriate cables

Key terms

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.
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.
Virtual LAN
VLAN
A logical grouping of network devices that behave as if they are on the same network regardless of physical location.
Physical Network Diagram
A visual representation of the actual physical layout and connections of network devices, including cables, hardware locations, and physical topology.
Logical Network Diagram
A visual representation of how data flows through a network, showing communication paths, IP addressing, and logical groupings such as VLANs independent of physical layout.

Transcript

Physical and Logical Topologies

When we interconnect our devices together, we're physically connecting them, so there's some sort of physical topology that we have. But there's also the way that communication can flow — there's a logical way that we can set things up. And we need different diagrams to represent those two different topologies.

A diagram is just a simplified drawing showing the appearance, structure or workings of something. Essentially, this is our map. It's a network map, it's a network diagram. We use these network maps and network diagrams to really understand what the flow is of our network, and if something happens, it helps us troubleshoot those issues.

Here's a topology that I use often in my lessons. We've got some sort of end devices that need to communicate to other end devices, and they're interconnected. These LANs are interconnected with these switches on these different networks, and then they're interconnected with this layer 3, these routers here. So it really represents all kinds of aspects from a layer 1, 2 and 3, and how they're interconnected. We may want to create network diagrams that show this physical, the data link, and the network layer, so we can understand and troubleshoot depending on what issues we're having on our network.

A Physical Diagram

The way that these physical and logical diagrams get represented could look wildly different. I just showed you one that I commonly use within my lessons, but this is kind of a representation of one I used in one of the places I worked prior to this. I had a physical diagram of how it was set up and a logical diagram of how it was set up, because I needed to know both physically how things were interconnected and how logically things actually flowed.

So this is what this looks like here. First of all, I had a layer 3 switch, and so this is representing a layer 3 switch. Now, we have not gone over what a layer 3 switch is — just know that it's like a router. So we essentially had a router that was functioning here at this level.

And then I had different buildings. Here's building A, B, and C. And then we had an annex, so this was like another building that was set off from the rest of the campus, and we needed to still get a connection to it. It was too expensive to run a physical line there, so we actually had a wireless bridge that was set up over to the annex. So this is representing how we had this router that was set up, and then maybe the main headquarters or the main building, and interconnected to these different switches here, and then interconnected this equipment.

A Logical Diagram

That's how it's physically set up, but logically the data flowed a little differently. Logically things were connected differently. What we had over there is we had this network for administration, one for operations, one for sales, one for all of the servers. Now, this is actually a college campus. It was actually much bigger than this, and we had a lot more VLANs and it didn't quite look like this, but let's just go with this right here.

From a logical perspective, how things were connected looked a lot different. For instance, this computer right here was connected to administration. Same thing with this one, same thing with this one right here. And then from a sales perspective, this laptop needed to be part of sales. This laptop, sales. This desktop right here, sales. And so it looked a lot different from a logical perspective.

You may ask, well, how does that happen that way? Well, we use something called VLANs. I'm not going to get into what VLANs are right here, but just from a really high perspective, VLANs broke apart these machines into their separate networks. So this was on a logical network called administration; same thing with this one and this one. They could all communicate together, but they couldn't communicate to the sales machines that were on these networks, because the VLANs didn't allow that.

So just realize here that we have physically the way we connect these different devices, but the communication could flow differently, and especially when we're dealing with VLANs, we'll want to represent that in a different diagram. So what we do is we set up a diagram that represents physically how things are set up, and then we set up a logical diagram of how things are set up logically.

About TechKnowSurge

TechKnowSurge builds IT and cybersecurity professionals through hands-on, concept-first training built around real understanding — not memorization. Free interactive tools, structured programs, and 25+ years of real-world experience, all in one place.

Explore free tools and programs →