Connect GNS3 router to Internet via Physical network adapter

LAB diagram

Step 1: Create a loop back interface. Open run and type hdwwiz.exe to open the “Add New Hardware Wizard”

Next

Select Install the hardware that I manually. Next

Slect Network Adapter. Next

Slect Microsoft/Microsoft Loopback Adapter. Next

Click Finish

Step2: Enable Internet connection in physical network adapter

Go to Start -> Control Panel -> Network and Internet -> Network Sharing Center, from the left pane click “Network Connections”, right-click your internet connection select properties and go to the sharing tab

Slect  Allow other network uses to connect through this computer's Inernet connection

Select options as shown in the screenshot above, the “Local Area Connection 3″ I have selected is the name of the newly created loopback interface which should be replaced by the name displayed in your system. 

Step 3: Assign loopback interface to C1 port.

You may have to restart your computer for this loopback interface to show up in GNS3. Open GNS3 by right clicking it and choosing “Run as administrator”, insert a cloud node into the topology, right-click select configure.

Step 4: Configure Router R1

R1>enable

R1#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#interface FastEthernet 1/0

R1(config-if)#ip address 10.255.255.2 255.255.255.252

R1(config-if)#no shutdown




Add a default route on this router.

R1(config)#ip route 0.0.0.0 0.0.0.0 10.255.255.1




Try pinging a public IP address and you should get a reply. Pinging domain names will result in an error as DNS has not yet been configured.

Configuring NAT for connecting to the internetBy now we have configured one GNS3 router to connect to the internet, if you connect more routers to this router connected to the cloud you will find that they are not able to communicate with the internet. This is because the physical machine does not know how to route the packets generated by the other routers of GNS3. The best solution for this is to perform Source NAT on the router connecting to the cloud. Take a look at the topology below which I will be using.

For R2 and R3 to connect to the internet we will be configuring NAT on R1 i.e. the router connected to the cloud.

R1(config)#access-list 10 permit any R1(config)#ip nat inside source list 10 interface FastEthernet 1/0 overload R1(config)#interface FastEthernet1/0 R1(config-if)#ip nat outsideR1(config)#interface FastEthernet0/0 R1(config-if)#ip nat insideR1(config)#interface FastEthernet0/1 R1(config-if)#ip nat inside The interface fastethernet 1/0 is the one c0nnected to the Cloud hence it is the outside NAT interface. The “overload” keyword is used as we are doing Port Address Translation. Both R2 and R3 must have default routes pointing to R1 else it will not work.