Gns3 Python

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  1. Gns3 Python
  2. Gns3 Python 3.8
  3. Gns3 Python Api
  4. Gns3 Python Appliance
  5. Gns3 Python Training

A practical, hands-on, real world approach to learning and implementing SDN and OpenFlow. Python for Network Engineers: Netmiko, NAPALM, pyntc, Telnet, SSH and more! Learn Network Programmability and Network Automation using GNS3 and Python.

4. Python (version 3) code to telnet to R1

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Gns3 Python

Next we create Python code to telnet to our R1 router, login with our provided username and password. It will also enter privileged mode (Router#) with “cisco” as the secret password. Then create a loopback interface 1 with IP address of on our router:

The source code can also be downloaded here.

Gns3 python networking

Note: The letter “b” in front of the string (for example in line: tn.read_until(b”Username:”)) indicates that the literal should become a bytes literal in Python 3. Bytes literals are always prefixed with ‘b’ or ‘B’; they produce an instance of the bytes type instead of the str type.

Save this code to the “” file to any location you want (we saved it in “C:/Users/PC/PycharmProjects/Python_Telnet/”). Then open command line and run this file as follows:

Gns3 Python

Of course you have to change the correct path to your Python file. Notice that we are using Python version 3 to run this file. If we are lucky, we will get a nice result like this:

Note: If you use some Python IDEs (like PyCharm) to run this file then the “Password: ” prompt will not be shown so please make sure to run it under “cmd”.

Now on R1 issue the “show ip interface brief” command to see our new Loopback 1 interface has been created:

Gns3 Python 3.8

5. Some errors you may see during the configuration

The hardest error you may see in this lab is the telnet connection to R1 does not work with the following error:

C:UsersPC>python C:/Users/PC/PycharmProjects/Python_Telnet/
Enter Username:R1
Password: (type “12345” here)
Successfully passed getpass
Traceback (most recent call last):
File “C:/Users/PC/PycharmProjects/Python_Telnet/”, line 8, in <module>
tn = telnetlib.Telnet(host)
File “C:Program Files (x86)”, line 218, in __init__, port, timeout)
File “C:Program Files (x86)”, line 234, in open
self.sock = socket.create_connection((host, port), timeout)
File “C:Program Files (x86)”, line 727, in create_connection
raise err
File “C:Program Files (x86)”, line 716, in create_connection
TimeoutError: [WinError 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond

Gns3 Python Api


Gns3 Python Appliance

To solve this problem we recommend you to:
+ Check step 3 – Verify the connection between our laptop and router in GNS3 carefully to make sure two devices can communicate normally
+ Try to run command line in Administrator mode (Search > Cmd > Right-click and choose “Run as administrator”)
+ Disable any firewall, antivirus software during the lab
+ Check the IP address of “host” in “” file carefully (it should be “host = “” in our lab)

Another problem we may encounter is after typing “Username: R1” and waiting for the “Password” prompt. The program is suspended:

Gns3 Python Training

As we said above, if we run this Python file through some Python IDEs (like PyCharm), the “Password” function of “getpass.getpass()” will not interpreted correctly and interrupted.