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Thread: GNS3-"Bridging" gns3 router to LAN with wlan adapter(laptop friendly)

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    Senior Member iproute's Avatar
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    Jan 2010
    Midwest, USA

    Default GNS3-"Bridging" gns3 router to LAN with wlan adapter(laptop friendly)

    I recently had need to run GNS3 on my laptop, connected to my LAN so my other workstations could communicate with it. Now I'm not keen on tethering myself down with an ethernet cable to do this and using my traditional method of adding a bridge adapter, tap adapter, then putting eth0 and tap0 into the bridge - will not work with wlan adapters. You end up with a message similar to the one below;

    darkside-ng ~ # brctl addif br0 wlan0
    can't add wlan0 to bridge br0: Operation not supported
    Here is a method that will work equally well. I say "bridged" because really this is a 'routed' solution. First you'll need to install GNS3, user-mode linux utilities, and your IOS image. For the IOS you could try a google search such as
    inurl:ciscoios c2600
    root@bt:~# apt-get install gns3
    root@bt:~# apt-get install uml-utilities
    root@bt:~# tunctl
    root@bt:~# ifconfig tap0
    root@bt:~# echo 1 > /proc/sys/net/ipv4/ip_forward
    Now start up GNS3, and add your IOS image. Add a router and start it. Make sure to calculate an Idle-PC value(right click on the router), otherwise your CPU will be under a heavy load when it does not need to be. Add a cloud device and bridge it to tap0 on the nio_tap tab(right click>configure on cloud device) by typing in tap0 and hitting the add button. Use a fast ethernet link between the router and the cloud device. Now console into your router from the right click menu.
    Router> enable
    Router# conf t
    Router(config)#int fa0/0
    Router(config-if)#ip address
    Router(config-if)#no shut
    Router(config)#ip route
    Router(config)#ip route
    Router(config)#ip name-server
    Now for your other workstations on the network to communicate with the device, you'll need to log into your router and add a static route for the tap0 virtual router subnet. Here is the linux command to do so as it is a nice way to describe the route. The gateway in this case is your workstation IP address. This command below is NOT meant to be run in backtrack but describes the static route that you'd need to add to your physical router. Clearly in this example my physical LAN subnet is
    route add -net netmask gw
    Last edited by iproute; 03-28-2011 at 10:46 AM.

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