Getting started with GNS3

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Today I made a post about using layer 2 switches in GNS3, but I haven’t done a tutorial on just the basics of GNS3. So here we are. Remember that GNS3 has come a long way since it’s first release and while this guide is produced on a windows machine, the basics are pretty much the same.

  1. Download GNS3, you have to register  but it’s quick and they won’t spam you
  2. Follow the on screen instructions with the installer, it’s an all in one so anything you don’t already have like WireShark it will download it for you.
  3. The first thing we want to do is add some routers, so open up preferences (View > Preferences)
  4. Goto IOS routers under Dynamips and click New. step4
  5. Now I am going to ‘provide’ you with some IOS images for use with GNS3, these are confirmed working and are an older IOS 12.x however they are fine for all your cisco studies. The routers we are going to add and I’ve provided are: 2691, 3725 and 7200. These are all the routers you will need! Download the IOS pack here:
  6. Extract the files and select the IOS image you want to use for most labs a 2691 will do so that’s what we’ll use in this example. GNS3 will ask if you want to decompress the image press yes. It will extract and copy the image for you, click next. step6
  7. GNS3 will auto detect the platform and appropriate RAM, you can increase it if you like then click nextstep7
  8. You will then be asked to slect slot cards, you can leave it or look up card numbers, otherwise click Next.
  9. Next are the WIC slots. You will want a WIC-2T for serial connections in most labs, then click next. step9
  10. You can now fiddle with the idle CPU values, most of the time they are auto-detected. click Finish finally!
  11. Now you have a 2691 in your router list! Click Apply then OK.
  12. You can now use this router in your topologies, click the routers tab and then drag the 2691 into the topology area.step11
  13. Right click your router and click Start. step13
  14. You will see your Router turn green in the Topology Summary pane. You can now right click you router and console into it! step14
  15. You now have a fully emulated working cisco 2691 router! step15
  16. Close the console (you can open any router console by double clicking the router) Drag in another 2691 router.
  17. Now click the connector tab and your mouse will turn into a cross-hair, click R1 and an interface menu will pop up. Let’s connect the serial ports, select Serial0/0 then click the other router and do the same.step16
  18. The routers are now connected and you will see the interfaces turn green.

That’s all there really is to it! You can add additional router models by following this guide again except selecting a different image in step 6. I have provided in the IOS pack 3 routers and these should be all you need for your studies.

If you want to add switches too you can read my tutorial on Layer 2 switches in GNS3

I hope this has been informative and helps you in your studies. Remember if you like it, share it! show some love @ompster

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