Layer 3 switches in GNS3

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I recently did a post on Layer 2 switches in GNS3 now I’m going to show you how to setup a layer 3 switch with in GNS3. What is the difference? Well there are many but this is not that kind of article. For starters show VLAN will give you an ambiguous command off the bat on a layer 3 switch. But basically a layer 3 or core switch can route between VLAN’s whether they or private or not ,etc.

The layer 2 switch i talked about in my other article uses IOS on Unix IOU. This method for the layer 3 switch basically uses a router image with a switching module. And yes you can do the same thing on real equipment!

First of all you are going to need GNS3 and some router images. If you need these you can read my article on getting started with GNS3 or you can go directly to the IOS pack for GNS3

  1. Go into the preferences Edit > Preferences and select the IOS routers under Dynamips
    step 1
  2. You can select one of your previously decompressed images in your GNS3 images folder (it’s ok if it’s already used for another router) I’m using the 3725 image
    step 2
  3. In this step make sure you select This is an EtherSwitch router and click Next
    step 3
  4. In the next step you can change the RAM but 127mb is fine. Then GNS3 will automatically select the switching module for you! as shown here. Click next
    step 4
  5. In the next few dialogues it’s just like adding any other image. Set the IDLE PC value ,etc then the EtherSwitch should appear in your list:
    step 5
  6. Now you should have a working layer 3 switch with about 16 ports!
    step 6

I hope this helps! remember you can use any router image all though I have only used the 3725 with this example.

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