CCIE Pursuit Blog

January 5, 2009

Dynamips for CCIE – Part 1 – What is Dynamips?

Filed under: Cisco,Cisco Certification,Dynamips,IOS — cciepursuit @ 12:05 pm

I’ve recently started using Dynamips for the vast majority of my CCIE lab study.  I had experimented with Dynamips in the past and found it very useful.  I really didn’t have a box capable of running Dynamips for full-scale labs vendor labs (IE in my case) so I used it primarily for short, “technology-focused” labs.  I recently upgraded one of my home boxes with new hardware and Ubuntu (Linux distro) and have started using IE’s Dynamips lab workbooks as well as a lot of their new Volume I labs (not specifically written for Dynamips, but easily convertible).

Anyhoo….I thought that I would share some of my experience with Dyanamips.

So what is Dynamips?  It’s basically a program that emulates the hardware of a number of different Cisco router platforms (7200, 2600, 3600).  Christophe Fillot is the author and maintains a technical blog here.  Since the software emulates the hardware you can run IOS on it and basically have a virtual router.  Better yet you can connect you can run multiple instances these virtual routers and connect them together to create virtual topologies.

Sounds great, right?  So Cisco is completely cool with this?  Actually, no.  In order to run a virtual router instance you need to have a copy IOS software to run on it.  The “letter of the (Cisco) law” states that “users may only run Cisco software on the Cisco hardware for which the user pays the appropriate fees”. This is discussed a little more in depth in this posting, but basically you are breaking your Cisco IOS terms of use by running IOS on Dynamips.  That said, it’s highly doubtful that Cisco is going to do anything about this (for a number of reasons) but I feel that it is important to let you know the “legalities” of using IOS images with Dynamips.

While Dynamips is an amazing program, it does require a lot of resources in order to run multiple instances of virtual routers.  If you’re going to use it for vendor labs, you’ll need to beef up your box.  The IE labs use 6 routers, 4 switches, a Frame Relay switch, 3 backbone routers, and a terminal server.  That’s 15 devices.  I broke down and bought a Quad core Intel CPU with 4 gigs of RAM in order to run the IE labs.  You can run smaller topologies on boxes with less horsepower.

I won’t pretend to know the reasons behind this as I’m not an OS guru by any stretch of the imagination, but Dyanmips seems to run much better on Linux than on Windows.  I am running it on Ubuntu 8.10.  You do not NEED to run Dynamips on Linux, but I’ve found (and read the same from others) much better response on Linux.

Most users do not work directly in Dynamips but rather interact with that program via a front-end program.  Two of the more popular front-ends for Dynamips are:

Dynagen – a very popular text-based Dynamips front-end.
GNS3 – A graphical Dynamips front-end (I use this).

If you’re interested in Dynamips, do yourself a favor and bookmark these sites now: – Tons of great Dynamips tips, tutorials, and labs.  Many with step-by-step videos. – A very good forum for all things Dyanmip.  This is your best resouce for finding out Dyanmips information and getting your Dynamips questions answered.

Tomorrow I’ll get review installing Dynamips (actuall GNS3).

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