Creating IOS Router Template

In creating a network diagram for the GNS3 project, you will create a router template. This section explains the procedure for creating an IOS router template that uses the IOS image file of the actual router.

Step 1: Prepare an IOS image file

You should save the IOS image file to local storage beforehand, and Cisco 3640 series IOS is relatively easy to obtain and use on GNS3.

Refer to the following article on how to download an IOS image file from your router.

Step 2: Open [Preferences].

Start GNS3 and click [Edit] → [Preferences] to open the [Preferences] window.

Step 3: Open the IOS router template creation window.

Select [IOS routers] and click [New] to open the Create IOS Router Template window.

Step 4: Creating the IOS router template

From the Create IOS Router Template window, create an IOS router template by specifying the required information.

IOS image file path

Select Existing Image and specify the path to the IOS image file.

Template Name

The router’s template name is the platform name by default, such as “c3640”. You can specify the name of the template if necessary. it is useful to know the IOS feature set and version.

RAM size

Determine the amount of RAM in the IOS router you want to emulate. there is a link to the Feature Navigator to find out how much RAM you need for the IOS you are using in the Feature Navigator.

Modules to be mounted

Select the modules to be mounted in the slot of the router. WIC can be mounted if necessary.


Specify Idle-pc value. When you click [Idle-PC finder], the appropriate Idle-pc value is measured. When an appropriate value is measured by the [Idle-PC finder], click [Finish], and the creation of the IOS router template is complete.

Step 5: Verify the IOS router template

Verify the contents of the IOS router template you created.

Creating an EtherSwitch router template

Using the actual IOS image, create an EtherSwitch router template for use as an L2/L3 switch. Just check [This is an EtherSwitch router] on the template name selection window.

Check [This is an EtherSwitch router] to automatically change the template name to “EtherSwitch router”. Change the name if necessary.

The slot1 is also automatically equipped with the “NM-16ESW” module; Fa1/0 to Fa1/15 can be used as switch ports.