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).


  1. The terms of use regarding cisco’s IOS was developed before Dynamips came out. Fact is, Cisco employee’s use dynamips internally. Yes they had that old school emulation platform that Cisco kept secret until Dynamips was popular, but then the cat was out of the bag. One of our Cisco Rep’s actually openly endorsed dynamips and wasn’t afraid to say it. And cert guard couldn’t get a comment.

    The best logic I’ve heard on the job: “Your use a QA lab to verify configurations before they roll out to production right? Dynamips is the QA lab that supports the Cisco devices. You’ve emulated your Cisco hardware that you’ve already paid for. The smartnet contract paid for the IOS’s that represent your equipment.”

    Makes sense, but still stretching it. Point is, Cisco would never push the issue, and I’ve heard this straight from Cisco employees. Now, does the TAC promote it? Thats another question…

    Comment by Luis Garcia — January 5, 2009 @ 3:16 pm | Reply

  2. I agree Dynamips is an amazing product, I can’t praise it enough. You can test a number of what if scenarios in a safe lab environment before inflicting them on your production environment.

    It does have some shortcommings however:
    1. No support for ISDN.
    2. Support for a limited number of hardware devices.
    3. Limited switching support.

    You mention GNS3 as the GUI front end to Dynamips. I personally prefer manually creating my own .NET files.

    Comment by Sean Evershed — January 6, 2009 @ 2:32 am | Reply

  3. Hi CCIE Pursuit,

    I would like to go the route of using the majority of my lab devices in practicing for the CCIE R&S Lab with Dynamips. Since it sounds like you are doing exactly what I plan to do, could you give details as to how you have your Dynamips setup? For example, what devices are you running under Dynamips, what devices are you not? For sure you must own a couple Layer 3 switches? I would like to know exactly how you have it set up. This would help me out greatly.

    Thank you very much!!

    Comment by DY — January 7, 2009 @ 1:56 pm | Reply

  4. My question is similar to #3’s except I’m newer to certification(currently seeking CCNA but plan to be at CCIE writing level in year and a half). Could you expound on drawbacks of using Dynamips as my only source for a lab. It certainly seems like it would do me fine through my CCNA and CCN(I)P. I ask because cost is a concern.

    Some background. I’ve been networking for networking for 10years, 5 with routers. I currently work for an ISP(er go CCIP).

    Comment by Patrick — January 8, 2009 @ 2:07 pm | Reply

  5. Patrick, CCNA/CCNP is no problem you can do it 99% with Dynamips. The only thing you will have to do with real equipment is part of the switching exam. I used 5-6 sessions which is under $100.

    DY, Dynamips can take care of a lot of stuff just suplement what it can’t with rentals it is much cheaper that way.

    All the best 🙂

    Comment by Branko Santo — January 11, 2009 @ 9:19 am | Reply

  6. Thanks for the follow up reply. Much appreciated.

    Thanks for this blog as well(meant to say that last time). It’s nice to come here and learn not only in knowledge but also in your experience. Helps the rest of us with knowing potholes/speedbumps may be in road ahead.


    Comment by Patrick — January 12, 2009 @ 11:17 am | Reply

  7. […] enigma for us as we are used to the tactile world of actual hardware.  Fortunately, we do not feel alone in trying to figure it […]

    Pingback by Dynamips & GNS3 Tutorial « Network Study Group - CCNA CCNP CCIE Blog — January 15, 2009 @ 8:09 am | Reply

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