GNS3 Basic Device Configuration

- select the contributor at the end of the page -
Once the initial configuration of the Cisco IOS images and GNS3 preferences is complete, it is time to begin the process of learning how to configure a device. As in real life, each device can be configured with a specific amount of memory, disk, and modules. Each of these will be covered in this article.

GNS3 Device Configuration

The process of configuring a device is not overly complex; however it is important that the basic network topology be worked out before starting configuration. This article is only going to be configuring a single device so the topology is rather simple; in this case a single 7206 device will be configured.

The first step in the configuration of a device is to add it to the GNS3 map. Figure 1 shows the 7200 device that will be used in this example.

Main GNS3 Map

Figure 1 - Main GNS3 Map

Figure 2 shows the process of dragging the 7200 from the node types pane to the main map pane.

Dragging a Device to the Map Pane

Figure 2 - Dragging a Device to the Map Pane

Once the device has been dragged over to the main GNS3 pane it will be displayed as shown in Figure 3.

Complete Map

Figure 3 - Complete Map

To configure the device it must be right-clicked and the Configure option must be selected from the menu. Figure 4 shows the menu that will be displayed when a device is right-clicked.

Right-Clicked Menu

Figure 4 - Right-Clicked Menu

Once Configure is selected the Node configuration window shown in Figure 5 will be displayed.

Node Configuration Window

Figure 5 - Node Configuration Window

To configure the device select it from the left pane. Figure 6 shows how the right pane changes when the device is selected. The general options available for the selected device are shown including any hardware options, depending on the platform.  In this case the 7200 platform midplane (how the modules connect to the NPE) and NPE (processor card) are configured from this screen.

Device Configuration Node Window

Figure 6 - Device Configuration Node Window

The memories and disks tab offers the ability configure the memory and disk allocation for the device. The size of the RAM required depends on the specific image being used; generally 256 Mbytes is sufficient for most images (to be sure, it can be checked at Cisco's Feature Navigator Site (linkto: The typical default NVRAM size is 128 Kbytes and the size of the disk depends on the specific requirements of the lab; generally a disk is not required for a simple lab.

Device Memory and Disk Configuration

Figure 7 - Device Memory and Disk Configuration

Figure 8 shows the “Slots” tab; the number of configurable slots that are available on each specific platform will be shown. In this case the 7206 supports a total of 6 full module slots and another slot that is part of the processor card (slot 0).

Device Slots Tab

Figure 8 - Device Slots Tab

Figure 9 shows the different options that are available in Slot 0 of the 7200 platform; as stated before, the options are limited because it is part of the processor card.

7200 Slot 0 Adapter Options

Figure 9 - 7200 Slot 0 Adapter Options

Figure 10 shows the different options that are available on Slot 1 (which will be the same with Slot 2 through Slot 6). From the options available, as shown in Figures 9 and 10, select the modules that meet the network topology requirements of the intended lab. For the purposes of this article it is not important.

7200 Slot 1 through Slot 6 Adapter Options

Figure 10 - 7200 Slot 1 through Slot 6 Adapter Options

The next tab allows the configuration of the configuration register; for normal operation this is typically set to 0x2102. The base MAC address can also be configured as well; this is handy if you are testing a feature that uses this value.

Advanced Node Configuration Tab

Figure 11 - Advanced Node Configuration Tab

Once the configuration has been completed, it is possible to see most of these options selected by putting the mouse curser over the configured device as shown in Figure 12.

Configuration Summary

Figure 12 - Configuration Summary


It is vital that to properly configure GNS3 to emulate a topology that the topology is laid out first, whether this is physically on paper or has been thought out mentally. While GNS3 will automatically select the appropriate adapters if links are created on the map, it is often better with more complex topologies to manually select the adapters to use on each device. Hopefully the content of this article will help in performing these steps for future emulation environments.

Get our content first. In your inbox.

Loading form...

If this message remains, it may be due to cookies being disabled or to an ad blocker.


Sean Wilkins

Sean Wilkins is an accomplished networking consultant who has been in the IT field for more than 20 years, working with several large enterprises. He is a writer for infoDispersion and his educational accomplishments include: a Master’s of Science in Information Technology with a focus in Network Architecture and Design, and a Master’s of Science in Organizational Management. Sean holds certifications with Cisco (CCNP/CCDP), Microsoft (MCSE) and CompTIA (A+ and Network+).