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.
Creating Simple Network Topology
Start the Emulation by Clicking Play Button.
Open the router Console Open up the console for router configuration.
Router configuration I also put the log which is generated by the router after some configurations. In router configuration, I configure Router Interface FA0/0 IP address 192.168.59.5, router’s default gw 192.168.59.2 and dns 8.8.8.8
R1#enable
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#interface FastEthernet 0/0
R1(config-if)#ip address 192.168.59.5 255.255.255.0
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-if)#exit
R1(config)#ip route 0.0.0.0 0.0.0.0 192.168.59.2
R1(config)#ip domain-lookup
R1(config)#ip name-server 8.8.8.8
Experiment
Next post will be about backing up and restoring router configuration via tftp. And It will connect to the physical tftp server.