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 Post subject: FAQ and Known Issues
PostPosted: Wed Oct 15, 2008 3:46 pm 
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Joined: Sat Oct 11, 2008 1:41 pm
Posts: 2668
Location: Canada
How to get started?
Please see documentation for beginners on GNS3 website:

Can you provide a Cisco IOS image to me?

No, we are not allowed to distribute any IOS image. You will have to find one by yourself, this should not be a problem if you are a Cisco customer.

Do you emulate Catalyst switches?

Although GNS3/Dynamips provides a simple virtual switch, it does not emulate Catalyst switches. This is due to the impossibility to emulate ASIC processors used in those type of devices.

On Linux / Unix / OS X, when I bridge a router or switch interface to my local host I can’t ping it from my host. But this works on Windows? What gives?

This does generally work on Windows (depending on your network card) but not on Linux / Unix. Most likely this is due to differences between libpcap and Winpcap, and the differences in the network stacks on Unix / Windows (e.g. NDIS). However you should be able to ping your bridged interfaces from other systems on the bridged network. If this does not work on Windows for your particular NIC, try creating a Windows loopback adapter and bridging to that. On Linux you can use a tap interface and the NIO_tap (available from a cloud). OS X you can install tun/tap drivers.

I have a complex lab with several routers, and my serial interfaces are flapping, eigrp neighbor adjacencies are failing, show run and write mem takes forever.

This is most likely a performance issue with the host PC. Large labs consume lots of RAM and CPU. By default, the router’s DRAM is simulated as a disk file of the same size as the allocated RAM. The host OS’s caching features will naturally try to keep the most commonly access pages in RAM. But as your RAM runs low, disk thrashing will begin. The virtual routers then become “starved” for CPU and start missing various hellos and such. There are several options for resolving this:

  • Use a more powerful host (more RAM and / or a faster CPU)
  • Distribute your lab across several hosts
  • Use lower-end virtual routers where possible. For example, a 3620 running 12.2 IP base only needs 32 MB of RAM and could be used when you need to simulate a simple LAN router, or “the Internet”.

Why my Wireless adapter doesn't work to connect to the real world?

Wireless NIC are known to have some problems with Winpcap and libpcap, those library being used by GNS3 for bridging with NICs. Workarounds exist on Windows and Linux, please see Bridge with a Wireless NIC on Windows.

Why my serial connection works though the interfaces are both DCE?

GNS3/Dynamips doesn't emulate the physical layer which is why the serial connections work even though they are both DCE.

What are supported models? What devices GNS3 can emulate?

Can I add new models and platforms in GNS3?

Dynamips (IOS emulator under GNS3) can only emulate Cisco routers listed in the above link. However, if you're willing to provide information or want to try programming hardware emulation, help is very welcome =>

Known issues
  • Configuration is not saved in 3745. Fixed in Dynamips >= 0.2.9!
  • Console is not opening with 2600. There is some bug in Dynamips regarding some IOS in 2600. Unpacking IOS might help. See GNS3 documentation for more information.

Last edited by flaviojs on Tue Sep 17, 2013 7:26 pm, edited 6 times in total.
c3745 bug not longer present.

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