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The Definitive Guide for Working with GNS3

In this video training course, CBT Nuggets trainer Keith Barker is your guide and introduces the typical issues facing every GNS3 user and, more importantly, how to overcome and solve each of these challenges. Topics in the course include running GNS3 in Windows, Mac, and Linux environments; how to integrate virtual workstations into the GNS3 topology; how to connect the virtual GNS3 network to a live network; and much more....
In this video training course, CBT Nuggets trainer Keith Barker is your guide and introduces the typical issues facing every GNS3 user and, more importantly, how to overcome and solve each of these challenges. Topics in the course include running GNS3 in Windows, Mac, and Linux environments; how to integrate virtual workstations into the GNS3 topology; how to connect the virtual GNS3 network to a live network; and much more.

GNS3 is a free, open-source tool that provides emulation of network hardware (such as Cisco routers and firewalls), so that customers can practice, configure, and troubleshoot network scenarios all in a virtual environment running right on their Windows, Mac OSX, or Linux computers. Multiple network topologies can be saved, paused and/or resumed on the fly so that the learner can practice at the convenience of their own schedule. GNS3 provides the emulation of the physical devices, and the user provides the OS image for the version/vendor of the software on which you want to practice. GNS3 is a fantastic tool, but there are a few stumbling blocks facing the typical user.

Note: The technology associated with this course is currently outdated. However, this course still retains value as a training resource.

Keith Barker has been a CBT Nuggets trainer since 2012 and holds a variety of networking and security certifications, including CCIE R&S, CCIE Security, (ISC)2 CISSP, Palo Alto CNSE, and Check Point CCSA.
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1. Welcome to GNS3 (17 min)
2. GNS3: Up and Running on Windows (38 min)
3. GNS3: Troubleshooting on Windows (30 min)
4. GNS3: Automating Initial Configurations (14 min)
5. GNS3: Adding Hosts with Virtual PC Simulator (34 min)
6. GNS3: VirtualBox Host Integration (39 min)
7. GNS3: Integrating DHCP and the Host PC (29 min)
8. GNS3: Connecting to the Internet (38 min)
9. GNS3: Protocol Analyzer (23 min)
10. GNS3: Custom Terminal Emulation (29 min)
11. GNS3: Trunk to Live Equipment (30 min)
12. GNS3: ASA Firewall (42 min)
13. GNS3: Ubuntu and Distributed Processing (29 min)
14. GNS3: AWS Cloud Hosting (20 min)
15. GNS3: Mac OSX (32 min)
16. GNS3: L2 Ethernet Switching (60 min)
17. GNS3: Connecting Virtual to Live Gear on the Mac (27 min)
18. GNS3: Trunking and Tunneling to Live Gear on Linux (23 min)
19. GNS3: Ubuntu, the ASA and Qemu (16 min)
20. GNS3: Creating a Frame-Relay Switch (18 min)
21. GNS3: Cisco Configuration Professional (18 min)
22. GNS3: NTP and CA Servers (19 min)
23. GNS3 v1.x Update (10 min)

Welcome to GNS3


Welcome to the virtual world of GNS3. On behalf of the entire CBT Nuggets family, I'd like to be the first to welcome you. I'm Keith Barker. Let's begin. Our objective in this video is simple. It is to identify how you can get the absolute most out of our time together in this GNS3 series.


I've learned that there's several different types of experiences that people have with GNS3. There's people who are brand new to it, who have never touched it. There's people who have been using it for years. And there's a whole wide range of everybody else in between.


No matter where you are on that scale, this GNS3 series has something for you. Let's take a moment and identify why GNS3 is so valuable to so many people. Let's imagine that you and I and a few other friends are planning a trip. And we're going to go on an airplane.


So we all meet early in the morning, and it's still cold, at the airport at 6:00 AM. We go through security. We get on the plane. And we discover, to our dismay, that the pilot, although he studied really hard, he's never actually flown a plane before.


Neither has the co-pilot, but don't worry they've studied. We, you and I, are off of that plane. We are not flying with a guy who's never really flown before. Well, as silly as that sounds, we have the same challenge inside our computer networks. Let's take this network right here.


We've got some switches and routers. We've got some WAN connections. We have an internet service provider. It's very unlikely that someone would trust you and I to work on this network had we never practiced hands-on configuring a network before. Even if we've studied in our minds and we've read and watched videos, it's important for us to practice.


So for you and I to get our hands-on practice there's three basic things that we can do, actually four. One's kind of silly. One is to use Notepad. And just put in the commands-- Notepad or a text editor-- and pretend that we're actually putting commands in.


Now, I've seen people do that. And that doesn't work for me because there's no response from a text editor. So you put the command in and you press Enter. And you think it's right. You hope it's right. But that's not really a great reinforcement. The next option is we could go ahead use a simulator.


Now that would also work for a pilot. Pilots have simulators. So they can practice and get a feel for it. And there's great simulators out there. So you can purchase a simulator. Practice with a simulator. You put the commands in, but it's not the real deal.


It's simulated. The next option, which is cool, is hardware. Now, in many companies, you may have racks of hardware that you can put together. Or you can go out and purchase hardware. I love hardware. I have hardware in my lab here at my home office.


Hardware is a great, great thing. What's the challenge though? Oftentimes, we don't have enough of it. If you have the hardware to practice with, it's not in production and you can go ahead and use it to reconfigure, that's fantastic. So if that option is open for you, go for it.


The other option is to go ahead and use an emulator. An emulator pretends. It pretends to be something. For example, if you want to run a PC in a virtual environment, there's lots of virtual environments to run a PC in. For example, you have Virtual Box.


You have VMware and others that can virtualize the hardware. So you might have an operating system like Windows. It's running inside of this virtual machine. It's not real. But the operating system doesn't know it. So the key is, when you bring up Windows and you run it, the Windows operating system doesn't know that it's not really running on physical hardware.


It's logically in some bigger server somewhere. We can do that same thing with GNS3 because GNS3, and behind the scenes something called Dynamips, it's an emulator. If we do a show version right here and we do a show IP interface brief and we do anything else, this is live IOS.


It's really running. It's not running on a real hardware platform. It's all virtualized. Now the benefit of that is, is that if we want to practice a network-- for example, let's say we're just dreaming and we're thinking, OK-- so the light bulb's going off in our mind-- I'd like to create a couple routers, a WAN link, a connection to the service provider, a switched environment, including spanning tree, we could actually do it.


We could emulate all this stuff. And actually run the software and have it respond like it would on live gear, which is pretty darn amazing. So the biggest benefit of GNS3 is that it gives us an emulated environment where we can emulate the hardware, run live IOS software, and actually practice the commands.


So the case is, before we roll this out, we could logically do it inside of GNS3. Practice all of it. And then have our design perfect before we roll it out on the production equipment. Another challenge that comes up all the time that makes GNS3 very, very powerful is the ability to validate what we think is happening.


For example, one of the concepts that we learned about is this thing called DHCP. In fact, let me bring up a topology in GNS3 to show you. So let's consider this topology. Here we have DHCP. And this is the inside of the network from a NAT perspective and the outside of the network from a NAT perspective.


This is R1. We have various interfaces. He's connected to the live internet. And everything from here over, this is all virtualized. The PC is virtualized. The router is virtualized. The connection to the Internet through my home network is real. And then of course, the internet's real as well.


But if we wanted to verify basic concepts like DHCP what's supposed to happen? Well, what we learn in technical books is that, well, DHCP here's what supposed to happen. The client does a discover. The DHCP server sends an offer this way. The client requests that.


And then the DHCP server sends an acknowledgement. So we have DORA, like Dora the Explorer. Now, that's great. And we can study that. But if we wanted to just confirm that that's really what's happening, one of my friend's Marvin says, Keith, the packets, they don't lie.


So what we could do is we could actually capture traffic on this wire right here. Check this out. I could say-- Oh, I have a capture running. Let me stop that capture. Let me start a new capture. And click OK. And then let's bring up that capture live.


So I'm going to start Wireshark. So here's a capture of everything that's happening on that wire real-time. So if we wanted to actually see DHCP, we could bring up this virtual machine like this. And I'm going to just bring this over, so we can see it all.


I'm going to right click on Disable for the network adapter. And then I've got to go back to Control Panel to start it. I'm going to start it again. And as I enable it, let's take a look right here at the packet capture. So that's capturing all of the traffic as it really happens on the wire, which is pretty darn amazing.


So you might look at this and say, wow, this Windows machine-- it's Windows XP-- what's all this traffic that's happening. Well, my friends, that's the native, natural traffic that that Windows machine is really going to generate. So I'm going to go ahead and stop this.


And we'll scroll up. Let's take a look at the DHCP, which was really our important part here. If we wanted to verify how DHCP worked, we could simply open it up. Say, OK, here's our DHCP. Let me bring this a little bit bigger so we can see all of it.


So here we have our discover, right here. That's the first packet. And the next packet, we have an offer from the server. Third packet, we have the DHCP request. And the fourth packet, we have the acknowledgement. And there's also ARPs and all the other traffic that you'd normally see on a production network.


So if you really want to dig down for understanding the protocols, how they work, built in to the installation for the all-in-one installer for GNS3, it not only includes all the back end stuff like Dynamips, it also includes Wireshark and the drivers to make that all work.


So you can just simply right click, start a capture, view it real-time if you want to. And as I forgot to do earlier, I'm going to go ahead and stop the capturing as well. Otherwise, that capture keep growing and growing up until the size limit that I set for it.


So that is just an incredible feature that's very, very helpful not only for just designing networks, but also for verifying that the network is operating and the protocols are operating as you thought they were. And it never ceases to amaze me what I find when I look at my own GNS3 networks with the protocol analyzer.


I'm always surprised. And it gives me an opportunity to dig deeper, and deeper, and deeper to find out what the real behavior of these protocols are, even ones I've thought I've known for many, many years. Another comment I get all the time is that, oh yeah, Keith, GNS3 is great.


I love it. Once I got it dialed in, it was fantastic. However, it doesn't do switching. And I think to myself, OK, I know it doesn't do advanced switching like at the CCNP and CCIE level, however, for basic switching let's take a look at what it can do.


We can do ether channel. We can do trunks, whether it's between switches or for a router on a stick configuration over to R1. We can do access ports. And we can use spanning tree. It also does VTP, if you care about VTP. So if you want to practice with some of those technologies, all of those that I just mentioned, are supported inside of GNS3.


And I've got a Nugget to walk you through exactly how to do those aspects as well. I've had the opportunity to work with a lot of wonderful people. And sometimes in live class I would have an evening GNS3 workshop. So I'd say, OK, class is from 8:00 to 6:00 or 8:00 to 5:00, whatever it is, let's meet here at 6:30 and we'll spend two or three hours on a GNS3 workshop.


And I'd have people show up every time. And people would bring their Macintosh. They would bring their Linux. They would bring their Windows machines. And I'd walk them through step-by-step how to systematically optimize get their machines up and running with GNS3.


And they were always blown away. But you know what? There's some common, basic things that apply to all those platforms that if you do you can have success with GNS3 as well. So in that light, I have integrated into this series mostly Windows, but also some Mac and also some Linux.


And here's what I'd like to ask you to do. Regardless of which platform you're running, I'd like you to watch all the videos in order. Now, why in order? Because every single Nugget, we're going to add some new concept to the mix. And a lot of the concepts apply across the board.


So we'll build a foundation. And as we continue to go, we'll build the concepts, and build the features, and build the add-ons. So when you're done, you'll have this tool belt full of options that you can use when building your own GNS3 topology. Secondly, besides just watching the video, I would also like you to draw out-- have some scratch paper handy-- because I'd like you to draw out the topologies that you would like to do.


It makes a lot of sense to do something like this. Before you go out and create something inside of a production network, or inside of GNS3 even, it's a great idea to have a plan. So for example, maybe an initial plan would be this, I want a router. And I want that one router to connect to router two.


And this will be FA0/0. That'll be FA0/0. And this will be FA0/1, FA0/1. And this'll be a switch and a switch. And maybe not even hang a PC off of it yet. And maybe create a loop back and have a loop back here with And maybe a loop back here with


And maybe a basic routing protocol, like EIGRP-- little chuckle there-- or OSPF. And I'm not going to have you do RIP. Friends don't let friends do RIP. So do one of those two. So this would be a design. And that's why I talk about drawing. Plan out what you're going to do before you go ahead and attempt to do it.


So once you plan this out, you'd also have to plant what addresses to use. So loop backs can be these. Maybe this is network, R1.1, R2.2. On these interfaces here, maybe this is 192 dot whatever. So plan out your network and draw it. So once you've drawn it out-- it could be a napkin.


It could be a paper towel. It could be a desktop. As long as you're not doing any permanent damage to a desk. Write it out. And then go to GNS3 and create it. So that's what I would I encourage you to do. Watch all the videos. As I create the topologies, draw them out.


And then, my friends, I would like you do most of them, whether you're on Mac, or whether you're on Linux, or whether you're on Windows. It doesn't really matter. The basic topology and putting the pieces together you can do on every single one of those platforms.


I would strongly encourage you to do it. So after you've been through five or six videos, you're going to get very, very good at creating topologies and making them work. And here's a secret. There's a little thing that happens after you've done a few and it works, and you make a whole new one and it works, and a whole new and it works, your confidence level is going to go up.


And then this whole thing about GNS3 itself, that won't become the obstacle to learning. You'll have GNS3 as a tool. So you can say, you know what? I want to take a look at MPLS and the labels. Or I want to take a look at IPsec and how IPsec encapsulates the data.


You could throw those topologies together very quickly because you're comfortable with your GNS skills of putting that topology together and in place. I would like to ask one request of you. And that is, as we go through these videos together and as you start building your topologies, you're going to have a moment where you're going to say, oh my gosh.


I can't believe that's working. That's great. Maybe it's your first GNS3 topology with R1 and R2. Or maybe it's a MPLS Layer 3 VPN infrastructure with service providers emulated and connected to live Internet and everything else. Whatever it is, what I would love you to do is take a snapshot of your topology.


Take a picture of your topology and go ahead and post it up on my Facebook page, Keith Barker Networking. I would love to share the moment with you of the oh my gosh. So if you would, do me that huge favor. Don't do them for every topology because you're going to have dozens after you get running with this.


But just take one that you're like, oh my gosh, I'm pretty proud of this. Grab an image of it. And paste it up on my Facebook page so that we can enjoy the moment together. I still get a kick out of it almost every time when I'm on a virtual machine and I'm going out to the live Internet from a virtual machine and it works because it's just so darn amazing.


So in that light, let me also answer another question that comes up all the time. Well, Keith, what hardware models are supported inside of GNS3 for emulating hardware? What hardware can we emulate? Let me launch a browser from this PC. And let's go ask Google.


So this right here is from this virtual machine. And let's go ahead and do GNS3 emulated hardware. And the top link walks us through the details of that. It's right from GNS3.net's website directly. And we scroll down. And it's going to talk about the models.


So 1700s, 2600s, 3600s, 3700s, various network models, various 7200 series, and so it has a list of all the physical hardware that is supported. So I normally get one of my favorites that just works for me all the time and then I just use that over and over again for all of my router models.


If I need to change it for some reason, I might mix it up, but that's a great idea as well. Grab one model that you're comfortable with, that works for you, and stick with it throughout your journey in working with GNS3. Another question I have all the time is, Keith, if I'm going through a Nugget, how do I optimize the time inside of that Nugget?


And the answer is lab up everything you can as you go through the Nugget. See, one of the cool things about CBT Nuggets is you can pause us. Try it. Pause me right now. OK, and then you can bring me back. And that pause can be as long as you need it to be.


So for example, if you're with me in the ASA firewall class and we're going through active active failover, you can pause me right in the middle of that and lab it up. Because the ASA is also supported inside of GNS3. I'll walk you through the steps of how to configure that and get that all working in this series.


So don't just watch it and enjoy it and learn it. Internalize it by practicing. So that applies to the advanced courses all the way down to network plus. If you're in network plus and you're learning about ARP, lab up a simple network and have maybe FA0/0 an FA0/0 here.


Put on a basic IP address. And in these videos I'm going to walk you through doing that several times. And then you can use protocol capture on that wire. And look at the ARP packets. And verify what's in them, how they worked, what was the Layer 2 addresses involved, what did the ARP request look like, DHCP, or any of the other protocols that are coursing through the veins of our network.


You can not only see them, but you can also analyze them. I have had an absolute blast in putting this series together for you. And when I say for you, I'm serious. I did it as if you and I were sitting right next to each other side-by-side, enjoying the time logically going through each and every piece to get GNS3 successfully up and working on your computer.


And I'm looking forward to seeing you in each and every Nugget in this series. I hope this has been informative for you. And I'd like to thank you for viewing.

GNS3: Up and Running on Windows

GNS3: Troubleshooting on Windows

GNS3: Automating Initial Configurations

GNS3: Adding Hosts with Virtual PC Simulator

GNS3: VirtualBox Host Integration

GNS3: Integrating DHCP and the Host PC

GNS3: Connecting to the Internet

GNS3: Protocol Analyzer

GNS3: Custom Terminal Emulation

GNS3: Trunk to Live Equipment

GNS3: ASA Firewall

GNS3: Ubuntu and Distributed Processing

GNS3: AWS Cloud Hosting


GNS3: L2 Ethernet Switching

GNS3: Connecting Virtual to Live Gear on the Mac

GNS3: Trunking and Tunneling to Live Gear on Linux

GNS3: Ubuntu, the ASA and Qemu

GNS3: Creating a Frame-Relay Switch

GNS3: Cisco Configuration Professional

GNS3: NTP and CA Servers

GNS3 v1.x Update

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Intermediate 11 hrs 23 videos


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Keith Barker
Nugget trainer since 2012