GNS3: First dates are special

You know, it’s the little things in life that can bring us the most joy–or make us giggle to ourselves like a little schoolgirl. Whichever works for you, I guess.

Today is a great day in Networktown, Studyville, and EIGRPburg, all thanks to my good friend GNS3. If you don’t know GNS3 yet, and you’re a network engineer, you need to ask her out on a date. She’s a really cool chick, and invaluable for my studies for my CCNP. I’m way too cheap and have too little room for a big lab environment of my own at home, and my day job isn’t all that fond of miscellaneous network changes on the production network. I can run GNS3 on my laptop in its own little environment and break it as much as I want.

Yes, I know, GNS3 wasn’t born yesterday and many people have already dated her before me, but there are so many cool things I’ve learned from her in the last few weeks! I never considered she could do all of this stuff–for the net cost of FREE:

  • Build networks with different router models and interface configurations–they don’t all have to be the same.
  • Want to invite some virtual machines to your network as “test” hosts? If you already have Virtualbox installed, just tell GNS3 about it.
  • (Kayso, I added this on 7/4/14) Snapshots like VMware or Virtualbox: just remember that you must save your router configs on the router AND save your project in GNS3, before your take your snapshot. Once you do, flipping back and forth between saved snapshots is pretty easy. Why do it at all? I wanted to set up a lab with all of the basic configs (no routing protocols configured) for each router already complete as my “base”, so I didn’t have to start over every time. I’ve also created a snapshot of a fully working EIGRP config that I can switch to, so I can work on finer points, like summary-address(es), or policy-based routing.
  • The biggest deal to me may be the Wireshark integration. Debugs on your GNS3 routers are good, but how about a live packet capture you can actively view with Wireshark? Again, just tell GNS3 where Wireshark lives on your computer and she’ll figure it out.

Here’s a screenshot of my EIGRP lab:



  • (4) Cisco 2600 routers: (2) FE, (2) Serial
  • (2) Tiny Core VMs configured for persistent hostnames and eth0 configurations
  • (2) instances of Wireshark viewing live captures of interface f0/1 on R1 and R4, icmp display filter

Thank you, GNS3–our love will only grow.

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