Polished: How to Find and Import Cisco Router Images (BIN/IMAGE) Into GNS3 (By ChatGPT)
To use classic Cisco routers such as the 3725 in your GNS3 labs, you’ll need the correct IOS image files. This guide explains where to find them, where to store them, and how to import them properly into GNS3.
Where to Store IOS Images in GNS3
GNS3 expects router images to be placed inside its dedicated IOS directory.
On Windows, the default path is:
C:\Users\<your-username>\GNS3\images\IOS
Simply drop your .bin, .image, or extracted IOS files into that folder.
If you received IOS files from another source (e.g., a .zip archive shared through Teams), extract them and place the contents into the images\IOS directory.
Where to Find Cisco Router Images
GNS3 provides a library of appliances and linked documentation. Cisco IOS images themselves are not distributed directly by GNS3, but some resources help guide the process.
A good starting point:
- Cisco 3725 appliance page:
(GNS3 Marketplace → Cisco 3725) - GNS3 Official Instructions:
Covers importing appliances and setting up IOS, Dynamips, and related options.
These resources walk through how to prepare and import older Cisco router images for lab use.
How to Import the Cisco 3725 Router Image Into GNS3
The following steps use the Dynamips engine inside GNS3.
Step 1: Open the IOS Router Import Wizard
- Go to Edit → Preferences.
- Navigate to Dynamips → IOS Routers.
- Click New to start the import process.
Step 2: Select Your IOS Image
- Browse to your c3725-*.bin image file.
- Choose Copy image to GNS3 images directory.
- Select Decompress when prompted.
(This speeds up boot time and reduces CPU usage.)
Step 3: Choose Router Platform & RAM
- Platform: c3725
- Recommended RAM: 256 MB
GNS3 will automatically suggest optimal values.
Step 4: Add Optional Hardware Modules
Depending on the lab you want to build, you can add modules to the router:
Common modules:
| Module | Purpose |
| NM-1FE-TX | Adds FastEthernet interfaces |
| NM-16ESW | Adds a 16-port switch module |
| WIC-2T | Creates serial interfaces (used for WAN labs) |
Add these in the Slots section of the import wizard.
Step 5: Set Idle-PC Value
Idle-PC prevents your CPU from spiking to 100%.
- Click Idle-PC.
- Choose Auto-compute.
- Select the entry marked with an asterisk (*) — this is the best option.
Step 6: Finish and Save the Template
Once completed, you now have a reusable router template inside GNS3.
Using the Cisco 3725 Router in Your Lab
(You can ignore this section unless your lab requires configuration.)
Add the Router to a Project
- Drag the C3725 template into your workspace.
- Start the device.
- Right-click → Console.
Basic Configuration Example
enable
configure terminal
hostname R1
interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
end
write memory
show ip interface brief
Serial Interface Example (Router-to-Router Link)
interface Serial0/0
ip address 10.1.1.1 255.255.255.252
clock rate 64000 ! Use only on the DCE side
no shutdown
✅ Your Cisco 3725 Router Is Now Ready for Use in GNS3
Once imported, you can create topologies, experiment with routing protocols, practice WAN labs, or run switching features using the NM-16ESW module.
