Configure GNS3 for Automation

In this guide I will demonstrate how to configure a GNS3 environment using a VIRL Layer 2 switch, and a 7200 series router. This How To will show the base configuration of iOS devices, how to make connectivity between your host machine and the emulated network devices in GNS3 . This How To assumes you already have GNS3 installed with iOS devices. If you do not know how to setup GNS3 in Ubuntu follow the How To guides in the related articles links down below.

Instructions

Follow these steps to configure GNS3 for Automation

First let’s create a project in GNS3 . Open up GNS3 and a window should appear titled “project”. Name your the title of your project whatever you want and click “ok”.
Now let’s place a few appliance in our working pane. For this demonstration i will be connecting a 7200 series router to my NAT appliance. Connected to that router will be a VIRL switch. This switch will be layer 3 and will be running OSPF to route between it and the router.

The NAT cloud appliance you see pictured will create a virtual network with a standard address of 192.168.122.0/24. Any virtualization you run in Ubuntu will use this default address space. Now we will configure the router. *** NOTE*** All base configuration for my devices will also be in my GIT repository linked in the related articles table below.

!!! Base Configuration for 7200 Series Router !!!

conf t
!
hostname R1
!
ip domain-lookup
!
ip domain-name test.lab
!
ip name-server 8.8.8.8 
!
line con 0 
 login local
 logging synch
 exit
!
line vty 0 4
 login local
 transport input all
 exit
!
username johnny priv 15 secret cisco
!
int gi1/0
 description ///CONNECTION TO INTERNET\\\
 ip address 192.168.122.20 255.255.255.0
 no shut
 exit
!
ip route 0.0.0.0 0.0.0.0 gi1/0 192.168.122.1
!
crypto key generate rsa modu 1024
!

Once you have pasted the base configuration lets test connectivity from router to its gateway and internet.

Now that we have connectivity you can start Automating the router. But what if we need to reach that layer 3 switch?? Now we configure dynamic routing and PAT on the router. Follow this code for this configuration.

conf t
!
int gi2/0 ! configure the port facing the switch
 ip address 10.10.10.1 255.255.255.0
 no shut
 !
router ospf 1 ! Configure dynamic routing and advertise the network to the switch
 network 10.0.0.0 0.255.255.255 area 0
 default-information originate
 exit
!
int gi1/0 ! set the port facing the internet to outside. This tells the router that this interface will do the translation
 ip nat outside
 exit
!
int gi2/0 ! Set the port thats having its IP addresses translated to the inside interface
 ip nat inside
 exit
!
ip nat inside source list NAT interface gigabitethernet 1/0 overload ! set the list and interface for translation
!
ip access-list standard NAT ! configure an ACL to define the IP addresses to be translated
 permit 10.0.0.0 0.255.255.255
 exit
!

Now that we have configured PAT let’s configure our switch. Again paste a base configuration in the switch.

!!! Base Configuration for 7200 Series Router !!!

conf t
!
hostname XX
!
ip domain-lookup
!
ip domain-name test.lab
!
ip name-server 8.8.8.8 
!
line con 0 
 login local
 logging synch
 exit
!
line vty 0 4
 login local
 transport input all
 exit
!
username johnny priv 15 secret cisco
!
int gi0/0
 description ///CONNECTION TO ROUTER\\\
 no switchport
 ip address 10.10.10.0 255.255.255.0
 no shut
 exit
!
ip routing
!
crypto key generate rsa modu 1024
!

Now that the base configuration it complete let’s configure dynamic routing on the switch do some verification commands.
```
conf t
!
router ospf 1
 network 10.0.0.0 0.255.255.255
 exit
!
```
Run a few show commands to make sure there is OSPF routing between the devices.

Now that we have verified we OSPF routing between neighbors let’s see if our switch can reach the gateway, our host machine, and then the internet! We will complete this with a trace route.