CCNP – Using GNS3 for certification studies

For those that have been reading my posts for the past week, you have read that I am studying for my CCNP Route/Switch certification to renew my existing Cisco certifications. Although I have a rack of switches and a rack of routers, I find that I cant test ideas out sometimes a little quicker or when I am traveling and cant access the lab gear remotely, I can work through some of the exercises for the Route exam. One that that I wish that GNS3 had is the ability to emulate Cisco switches. After reading through quite a few of the forums posts on the GNS3 website forum, I understand that due to the way that Cisco has designed the switch hardware, it will be nearly impossible to reproduce it in software. Having said that, there is a lot that you can do with GNS3.

The biggest challenge for some folks is to get a copy of some flavor of IOS to work with. If you don’t work for a company that has Smartnet on their Cisco gear, there is a way to get a copy of IOS. All you need to do is buy a Cisco router of one of the models supported by GNS3 and you are on your way. If that is the route you need to go, I would suggest purchasing a 2611XM router. The XM is important because you can put more memory in the router to run the newer versions of IOS. You can also put a 4 port ethernet card as well as several WIC-1T/2T cards for ethernet and serial connectivity. You can look at other router models, this just happen to be one of the models that I have more of in my lab and it was a little more flexible in terms of the modules that you can install in the router.

I have used both the Mac and Windows versions of GNS3. I have been able to emulate the ASA on the Windows version of GNS3 but haven’t been able to get it to work on the Mac. It is something that I am probably doing something wrong since I can get it to work in Windows. I would strongly encourage you to have as much memory in the machine you are running GNS3 on. The Windows version seems to be a little more needy on having more memory but I attribute that to Windows itself. I have run around 20 routers on the Mac version of GNS3 without any problems with just 4 GB of RAM installed. I have only been able to get about 5 to 7 routers to work before the Windows machine locks up or just stops responding. I have also seen references to a Live CD Linux distribution that gives you a ready to roll Linux implementation without having install Linux and then GNS3 before you get it running.

One thing that I would encourage you to do is get GNS3 to find the optimal IDLE PC value to keep your machine from having Processor related issues where the CPU will go to 100% and stay there for varying periods of time. Something that I also to remember is to stop the routers in a particular configuration before closing the project to keep from having random configuration corruption. As a failsafe, I have created a Stack in Evernote and then create a Notebook under the stack for each Project. Even though the individual router configs are saved in GNS3, I use the individual Notebooks to back up the project with an individual Note to hold each device’s config.

One of the features I have been using more as I create additional projects for the different Labs or concepts that I am working through is drawing a circle around parts of the network to flag what routing protocol is used in a particular grouping of routers and labels to indicate the AS or Area number for the routing protocol or subnet address range that a particular area is to use. One of the steps that you are encourage to do is to uncompress the IOS image that you are using for the router. At this point, I have only been able to find the directions on how to do that for the Windows platform. I have been able to use a non-uncompressed image without any perceptible problems. There is a lot of good documentation on using GNS3 and it features. I would encourage you to review that as you start using GNS3. I have been using GNS3 on and off for the past couple of years and have noticed significant improvements in features and usability with each new release. Another interesting feature to try out is the Cloud option. This allows you to “connect” your GNS3 lab situation to the outside world. With this, you can experiment with accessing a real NTP server and other things that you will use on a production network.

Bottom line is that even if you have your own collection of routers and switches, there are quiet a few things that you will be able to use GNS3 for as you study for your certifications or just want to try something new out before doing on a production network for the first time.

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