GNS3 offers multiple ways to emulate IOS. For older images, we use and maintain Dynamips; an emulator dedicated to emulate some Cisco hardware. Dynamips can run unmodified IOS images. In the new GNS3 1.4, there is a way to run a second category of switches and routers. These are classified as Routing and Switching virtual machines (or R+Svms) for short. What are the differences Here are the major differences:
Only the c7200 series get newer IOS 15 images. All other platforms are now end-of-life and only support IOS 12.4. Please note that the IOSv appliance is based on IOS 15 and there are IOU (IOS on UNIX) images with IOS 15.
You will find the technology train images to contain the newest features but it may also contain the most bugs. We recommend Mainline over Technology train if you are interested on stability without the need of new features.Please see Cisco IOS Versions and Naming for more information.
When Dynamips runs an IOS image, a single instance can consume 100% of the processing time for a CPU core or thread. To remedy this, you can supply Dynamips with an Idle-PC value, to consume less CPU. This value will vary between devices/images. To help automate the process of determining a valid Idle-PC value, you can use the Idle-PC finder button when importing a supported IOS image into GNS3:
If you require more switching features, it is recommended to use larger Virtual Machine Switches and Routers (like the ones from VIRL) that run inside your choice of Qemu, Virtualbox or VMWare. For advanced switching IOSv and/or IOU is recommended.
IOU is a less resource intensive alternative to IOSvL2, but the images are not publicly available. You will need to get them from someone who works at Cisco. In addition, as this is a Cisco internal tool, IOU mages may be buggy and no support is available.
Use this if all you need is a basic switch to connect devices in a GNS3 topology. You cannot configure this switch through a CLI, but you can set the number of ports supported on the switch and other basic settings.
This is a rather simple process, but be aware that your options for configuring Cisco switching while using a c3640, c3660, c3725, and c3745 for this are quite limited. Refer to the switching section of this document to see what features will be unavailable to you.
Notice that slot 0 is still prepopulated with the GT96100-FE Dual FastEthernet adapter, and slot 1 will have the NM-16ESW module preinstalled. Never attempt to replace that GT96100-FE adapter with a switch module, as it will not work. You can add a second NM-16ESW,a NM-1FE-TX single FastEthernet adapter, or an NM-4T serial port adapter to slot 2.
When you add this Etherswitch Router to a topology in the Workspace, there is something you must be aware of. The first two FastEthernet ports (fa0/0 and fa0/1) provided by that GT96100-FE are routed ports only! This is by design, and they cannot be used as switchports. If you left the default NM-16ESW adapter installed in slot 1, the switchports will be interfaces fa1/0 and go through fa1/15:
By using the vIOS-L2 image, you can use many switching features such as Etherchannel, DTP, HSRP, Port Security, VLAN Routing, Switchport, 802.1Q, Trunk Port, Access Port, Spanning Tree Protocol, Port-Channel (Pagp / Lacp).
Here are a few additional Cisco Router images. For example, if you use a c1700 series Router, it will be insufficient because it does not support some features when you create a more advanced network topology.
After downloading one of the iOS images to your computer, you can watch the video below to add the image file to the Graphical Network Simulator-3 and also subscribe to our YouTube channel to support us!
IOS image is software or Operating System used in most Cisco routers and switches. IOS images support different packages like routing, switching, and inter-networking, etc. You can use these IOS images with GNS3. Gns3 is one of the famous network simulators and its hot feature is that it can run the real Cisco IOS image, as compared to another network simulator like packet-tracer which performs all functions based on programming. If you are a beginner then learn more here:Cisco Switch Basic Configuration, how to use or configure GNS3
Cisco 3700 Series are the multi-service routers that provide LAN/WAN connectivity, new high-density service modules, and support for multiple advanced integration modules. You can use the NM-16ESW module with this 3745 IOS, which will enable the switching functionality in GNS3. In this way you will be able to perform different switching labs with GNS3 like Vlans, inter-VLAN (Router on a stick), VTP (VLAN trunking protocol), different multi-layer functionality, etc. learn more about Layer 3 Switching vs Routing
GNS3 is free network simulator software. It emulates and simulates routers, switches, and other networking devices. Cisco uses proprietary software for its routers and switches. This software is known as Cisco IOS. GNS3 can run Cisco IOS. Since Cisco IOS is protected by copyright laws, GNS3 does not include any Cisco IOS in its default installation. It only provides a platform to use Cisco IOS, but it does not provide any Cisco IOS itself. To use a Cisco device in GNS3, you need to download and import its IOS to GNS3.
On specialized hardware such as Cisco switches and routers, the operatingsystem (here IOS) works tightly with some underlying specific (and usuallyproprietary) hardware and delegates parts or all of the processing to dedicatedchips, the Application Specific Integrated Circuits or ASICs, to allow faster processing.
Most of the switching logic of Cisco Catalyst devices is implemented at thehardware level.Thus, emulating a Cisco catalyst device to run its IOS images would implyto reverse-engineer and reimplement most of the switch features.
On the other side, most of Cisco routers logic occurs at the software level aspart of the IOS firmware.Emulating a Cisco router hardware to run its IOS images is therefore easierthan emulating Cisco switches.
They have no switching capability, but they remain useful when you want totest some feature specific to IOS 15.x (for instance entry-level Ciscocertifications require students to be familiar with the new licenses managementfeatures which came with IOS 15.0).
If the selected device supports EtherSwitch modules, a supplementarycheckbox labeled This is an EtherSwitch router becomes available.This checkbox tells GNS3 to consider this device more as a switch thana router.
Several IOU binaries are available, emulating various options but moreimportantly emulating devices acting at the layer 2 (switching) or the layer 3(routing).Layer 3 is well covered by Dynamips, however IOU is a really interestingalternative to test some layer 2 functionalities not available when using Dynamips.
vIOS usually presents itself as a virtual machine image hosting IOS.It is very similar in its form and behavior with IOU, there are imagesavailable for the layer 2 and 3 but layer 2 are the most useful ones (IMHO).
For performance reasons, a lot of switch things are actually not part of theIOS code but are implemented in hardware.This includes the ARL, or Address Resolution Logic, which provides all themethods to add, remove and lookup entries in the MAC address table. 153554b96e