So, as I previously mentioned, I'm currently re-certifying my CCNA qualification and running through the ICND2 study guide. Having worked through the first major section, which covers VLANs, STP and VTP (as well as some misc items) I wanted to incorporate this into GNS3. My primary reason for this is that Cisco Packet Tracer, while handy and free, doesn't simulate some features properly and is missing some functionality. I prefer to be working with something more realistic so set about setting up a switch in GNS3. If you're not already aware, GNS3 doesn't support Cisco switch images like it does routers because it is unable to emulate the ASICs used in Cisco switch hardware.
While you can use an EtherSwitch module in the 7200 router, this also lacks some of the functionality and commands of a full switch. Having done a quick bit of searching online, I found the best solution would likely be using Cisco Virtual Internet Routing Lab (VIRL), or the Cisco vIOS-L2 image. Unfortunately I can't afford $200 at the moment for a VIRL licence so after some more searching I found this great blog by Nathan Ash, which provides a demo version of the vIOS-L2 image and a walk through of installing it in GNS3. As Nathan's walk through works well, I won't be repeating the installation instructions here but will instead go through some of the caveats I have found of using this demo version. As this is a demo version of software, it's been explicitly designed to not function in a production environment. More specifically, every time the image is loaded it resets a bunch of stuff to some pre-configured settings, which is a minor pain but not the end of the world. Here's the problems and solutions: RAM hog! The QEMU process for each switch takes up a bit more RAM than the standard IOS images. Around 500MB per device, so make sure your machine can handle the number of devices you want to run. Boot time is a little longer and a bit more resource intensive than the standard IOS images. When booting a single QEMU VM, it will usually chew up around 20% CPU (that is running on an i7-3630QM processor. This will settle down to 2-3% at idle but only after the vIOS has performed an internal validation check. Once the message below appears, the CPU will settle down. "%PLATFORM-5-SIGNATURE_VERIFIED: Image 'flash0:/vios_l2-adventerprisek9-m' passed code signing verification" config-register command is missing. Not sure why you'd need this in a VM but was something I found when trying to get the demo version to stop resetting itself. Your startup-config file will be erased when the IOS is reloaded. Solution is simple, and good practice for the real world, maintain backups. When you're done with your lab for the day, or you want to reload a switch for whatever reason, copy your startup-config/running-config to notepad and save it somewhere on your machine. When the device boots again, copy and past in your config and off you go again. Vlan.dat re-appears on reload. As mentioned above, the demo version of software has some pre-configured stuff when it loads and this is one file that is generated and automatically populated. If you don't want it, the solution is simple, as soon as the switch loads, delete VLANs 100, 200 and 300 and delete vlan.dat from NVRAM. You can do this from global configuration mode with the following set of commands. no vlan 100 no vlan 200 no vlan 300 delete vlan.dat Lastly, just a quick note about GNS3 (mostly for my own future reference). If you love the classic Cisco green in your terminal and are using the default terminal emulator (PuTTY) provided with GNS3, you can configure this in GNS3 by clicking on Edit > Preferences, then on the General page select the Console applications tab, then in the Console application command for Telnet field, amend -skin 4 to be -skin 3. So the final command should be this: putty.exe -telnet %h %p -wt "%d" -gns3 5 -skin 3 And if you don't already have Cisco IOS images you can download some from the page below (Including a version 15 image for the 7200 series router). http://srijit.com/working-cisco-ios-gns3/ Sludge
2 Comments
Adesina
6/7/2017 01:29:07 am
Thanks for the explanation. I was able to installed vIOS today using your link. I am still trying to get familiarized myself with it as the graphical interface is a bit different with IOS in GNS3.
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Mharlo
7/1/2019 01:08:39 am
asa
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