Connect to Real World With GNS3

GNS3 is a GPL licenced cross-platform network simulation program. It enables us both virtual and physical networks operate together. It emulates Cisco IOS, doing so we have real Cisco device capability in a Virtual Machine. You can also analyze the packets with Wireshark. One exception that GNS3 has limited device capability as some Cisco devices impossible or  very difficult to simulate them. Also some devices need real hardware to operate. For supported Cisco devices and FAQ, Link.

My system runs on a Virtual Machine which is Ubuntu 16.04 LTS. Router model is 3745.

1- Creating Simple Network Topology.

It is depicted in the Figure-1 all in one picture.

all in one


2- Start the Emulation by Clicking Play button. Figure-2






Figure – 2

3- Open the router Console

Open up the console for router configuration. Figure-3




4- Router configuration

I also put the log which is generated by the router after some configurations. Only apply the command which starts by #.

In router configuration I configure Router Interface FA0/0 IP address(, router’s default gw( and dns(

R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#interface FastEthernet 0/0
R1(config-if)#ip address
R1(config-if)#no shutdown 
*Mar 1 00:03:47.627: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar 1 00:03:48.627: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R1(config)#ip route
R1(config)#ip domain-lookup 
R1(config)#ip name-server

5- Experiment

It is time to test whether or not I am able to connect real world. I ping the I successfully ping the Figure-4





Next post will be about backingup and restoring router configuration via tftp. And It will connect to the physical tftp server.

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