One of the interesting things about GNS3 is that you can connect your topology to the real world. For some of your CCNA and CCNP studies you may need to run an actual Web browser or Cisco’s Security Device Manager (SDM) among others. Just connect your topology to your real PC. You could even connect to virtual machines running on your computer inside VMware or Virtual PC. I’ve even set up two copies of Windows XP Professional running inside VMware virtual machines. Then, I ran Cisco soft IP Phones that could talk to each other. You could connect your virtual network to a real network as well. Connecting a virtual topology running within GNS3 to real devices is very exciting, but again, your throughput is going to be limited compared to using real equipment for the entire topology. It only makes sense to use GNS3 in a lab environment and for learning purposes.
For Windows users, click on the box directly beneath Generic Ethernet NIO, and choose the network adapter you wish to use. For Linux users, click on the drop-down box to choose your network adapter (either your real adapter or a loopback adapter). Click the Add button and OK. You will need to configure the IP settings for your computer’s adapter, and then use theAdd a link toolbar button to create your connection.
You may use your regular network adapter, but I usually create an MS Loopback adapter to connect to. In Windows, use the Add Hardwarewizard in Control Panel. Choose “Yes, I have already connected the hardware.” On the next screen, choose Add a new hardware device at the end of the list and click Next. Choose to “Install the hardware manually…”and click Next. Choose Network Adapters in the list and click Next. ChooseMicrosoft as the manufacturer and then Microsoft Loopback Adapter as the network adapter. Finish the wizard. Then right-click My Network Places and choose Properties. You may wish to rename the new Local Area Connectionas MS Loopback Adapter. Also, assign the proper IP settings to the adapter in order to connect to your topology. Linux has a built-in loopback adapter already installed.
Now start your router and assign an IP address to the interface that is connected to the Cloud. You should be able to ping from the router to your PC (loopback interface) and the other way around. Don’t forget to deactivate any firewall that could block pings on your computer.
R1(config)##ip name-server 220.127.116.11
R1(config)#access-list 1 permit 192.168.138.0 0.0.0.255
R1(config)#ip nat inside source list 1 interface fa0/0 overload
R1(config-if)#ip nat outside
R1(config-if)#ip nat inside