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Five routers on your laptop

In case you've missed yesterday's post … the weather was just way too good to stay in the office :) However, even if I would decide to work on my routers, I could take them with me (well, the laptop would be a bit heavy and the sun was too bright) thanks to Christophe Fillot (Dynamips) and Greg Anuzelli (Dynagen).

In case you haven't heard about Dynamips/Dynagen yet: Dynamips emulates a variety of IOS platforms (from 2600 to 7200) on Intel platform and Dynagen provides friendlier user interface (more than friendly enough for me, probably too cryptic for GUI addicts). I've seen Dynamips a year or two ago, checked what it can do and decided to stay with the real routers in a remote lab environment. In the meantime, the software has improved drastically, allowing you to test all sorts of IOS features and topologies, as long as you don't expect QoS to work or real-time features to act in real-time (simulation is, after all, a bit slower than the real life).

To start using this tool, download it from, read the tutorial and you're in business. I will also start providing more interesting scenarios in the dynagen configuration file format.

Let me conclude with a few tips:
  • If you don't need 7200-specific features, select 37xx or 26xx platform, it consumes less virtual memory per router.
  • Setting idlepc is mandatory if you want to have decent response. Read the tutorial, the idlepc section is great.
  • Unzip the IOS files. With uncompressed files, the routers are ready to be configured in under a minute on my laptop; if the IOS image is compressed, it takes several minutes.
  • If you have larger topologies, use GhostIOS and Sparsemem features.
  • Reduce the size of NVRAM and Flash to minimum that would work. These are stored as persistent files on your disk; you can have 256MB Flash if you want, but then you'll have 256MB less of your hard drive (per router).

With all the above-mentioned features enabled, I was easily running eight 3700-series routers on my laptop (IBM T60).

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  1. Can you run the whole Internetwork expert CCIE lab , i.e 13 routers si,ultaneously on IBM T60 laptop.

    Thank you

  2. Never tried it. A single router running OSPF and BGP (plus a zillion other processes IOS starts by default) consumes around 20% of CPU (40% of one core), so my eight routers consume 100% of both cores. That's not a real problem, as long as the routers can respond to routing protocol packets (and they are still OK in my scenario, no dropped adjacencies).

    I have no idea what they want you to start in the 13-router lab, but if there are many concurrent features being configured, you might get over the edge.

  3. Hi Ivan,
    I have been using it since its early developments! Now, i can load the full IEWBv4 topologies (6 7200s, 4 3640s-NM-16ESW, and 3 7200s as Backbones) with my CPU goes no more than 50% :) My Dell laptop is powerful enough and i bought it for this purpose! It is Intel Core Duo 2.2 with 4 GiG of RAM, yeeeha! and yes, it has a HDD with 7200RPM, too bad no SCSI yet! ;-)

    It works great! Dynamips is a wonderful wonder!

  4. Hi, Abdulla.

    What model is your laptop.

    I am on the verge of buying a laptop for the same purpose.
    I was going for IBM T61 but I will consider your option also .

    Thanks & regards

  5. Hi intikhab,

    My laptop is Dell Vostro 1500 with full options that are found on dell website. Quite expensive though! BTW, i ordered Vista ultimate but i ended up removing it because it...ah... it sucks!! :) i could not stand it and put windows XP instead to save my CPU and RAMs! Oh beside the irritation of the security messages that pops up every now and then...that made it REALLY sucks!!! ;-)


  6. Hi, Abdulla.

    There are a couple of new options with Dell now .

    XPS M1130 and inspiron 1520 with core2 duo T7500 processor.


  7. What are the ethics of using the IOS images with Dynamips?

  8. "What are the ethics of using the IOS images with Dynamips?"

    Good question, and I'll answer with another, what are your ethics for using any software in a non-production environment explicitly for testing purposes?

  9. "what are your ethics for using any software in a non-production environment explicitly for testing purposes?" - excellent and well thought reply.

    Although interestingly, it actually is in a kind of a production environment.. virtual servers can be added, multiple external interfaces can be added, acl's applied and OSPF is still producing its coded production purpose and ultimately even, it's not long before home systems will also be able to produce enough power to enable realtime clocking and functionality... (okay ASICs, TCAMs, Int Buffs and much more to consider for a full functionality).

    I am surprised Cisco hasn't tried to buy this out yet.. one can only presume they decided it's easier to copy.

  10. What's the ethics of being a company that makes a shitload of money by selling overpriced hardware, and proprietary software?

    What's the ethics of gaining market control, using outdated shitty hardware and software?

    It's OK to take proprietary software, you are not stealing, you are freeing something that was first stolen from the community.

    But Better than that is trying to use Free Software as much as possible.

  11. I want to take ccna exams and I want to use dynamips and dynagen. I don't have cisco IOS image files. Please help me in getting the cisco IOSimage files,

  12. Mohammed,

    while we might discuss whether it's OK to use the IOS image you're entitled to on non-Cisco hardware, supplying IOS images to third parties comes (in my understanding) close to software piracy. I really cannot help you.

  13. I have Dell Inspiron i3 laptop and want to setup the entire INE wb on it will be it possible have anyone tried it and can i get better response without my device being hanged ?

    Please let me know
    3 GB Ram
    Processor -i3 2.13GHz Intel Core
    Windows 7


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