Control CPU usage in GNS3 / Dynamips with Process Lasso

GNS3 Kills my system

I have been a user of Dynamips/GNS3 for several years now and I canít imagine what I would do without it. I use it for doing Proof Of Concept work and for Studying. Recently I have been throwing more and more Labs together to help me study Service Provider topics. I was getting frustrated when firing up six or seven routers and my system coming to a standstill, worse still spending ages configuring idle PC values.

The PC I am using is a HP ML110 Xeon Dual Core 4GB of memory running Windows 7 x64, so its no slouch!

Process Lasso

I remember a few year back I got a process scheduling freebie from a HP partner which did a great job of keeping Dynamips in check, so I did some searching but could not find that product, plus it costs money, but during my searching I stumbled upon Process Lasso.( I have configured Process Lasso as following on my GNS3 system. (I still use the free version as it meets my GNS3 needs)

Options – >Configure Default Priorities ñ> setup dynamips-wxp.exe as below normal



This ensures my system only runs at 95% CPU usage and the system is OK for mouse and keyboard input. When I am running GNS3 I tend to dedicate the system to this and I would not be running anything else like email or other surplus programs.


If you use GNS3 then I recommend trying Process Lasso to help keep you system responsive. As my labs grow bigger I will personally get a better feel for how Process Lasso performs, hopefully not to the detriment of Dynamips. Good luck with your GNS3 labs.

  • Terry Gwazdosky

    Nice find! Thanks for sharing. :)

  • Sharky

    Six or Seven Routers are noch so much. What kind of router did you chose 7200? On janaury i bought a intel ssd 80gb. It¥s a new world of speed to use it with gns3.

    • John McManus

      I am running 2961s at the moment since the do all I need. I will move up to the 7200 if the Labs need it.

      Whenever I have run GNS3 in the past whether it is 1 router or many the way it is coded (with out proper idle pc values) it would cause the system to be unresponsive and stick the processor(s) at 100%, so far using this process lasso I have not run into that problem.

      I would love and SSD drive for my laptop as I have heard fantastic things about the performance.


  • Ronald

    Have you tried recalculating IDLE PC timers?

    • John McManus

      Yes, when building a fix lab for long term use I make sure I adjust idlepc. But even doing that can still cause 100% CPU usage, so process lasso help me trim that a bit and keep the system responsive.


  • Carlos Fontes

    I need the release of the IOS for students and research, therefore I intend to live deeply and to breathe the world in Cisco and intend to improve the world of the communication.

  • Darren

    I’m quite surprised you’d be happy witting with 95% CPU usage.

    I’ve got over 18 routers running in my MPLS/MP-BGP setup on my dynamips box at home. It’s got a very cheap (£75 at the time) quad cpu and an el cheapo 4GB DDR2 kit. Once I got my idlepc set up correctly, the CPU never EVER goes above 40% – I could probably get away with even less RAM as well, 4GB was overkill.

    When doing the idlepc’s at first I ensured I had tons of config on all the routers – OSPF, EIGRP, RIPv2, BGP, MPLS and so on. Maybe that made the initial difference?

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  • Mark

    Thank’s for hint. Helps a lot