How to Use Python to Perform Network Automation on Cisco Routers and Switches

Today in this article we will see how a python script automatically logs into a Cisco Router/switch using telnet and configure a loopback interface or vlans.

Here is our topography:

Here is the working Python script sample from python’s website

import getpass
import telnetlib

HOST = "192.168.146.132"
user = input("Enter your Telnet Username: ")
password = getpass.getpass()
enablepassword = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until(b"Username: ")
tn.write(user.encode('ascii') + b"\n")
if password:
    tn.read_until(b"Password: ")
    tn.write(password.encode('ascii') + b"\n")
    
tn.read_until(b"R1>")
tn.write(b"enable\n")
tn.write(enablepassword.encode('ascii') + b"\n")
tn.write(b"configure terminal\n")
tn.write(b"interface loop0\n")
tn.write(b"ip address 8.8.8.8 255.255.255.0\n")
tn.write(b"end\n")
tn.read_until(b"R1#")
tn.write(b"show ip interface brief\n")
tn.write(b"exit\n")
print(tn.read_all().decode('ascii'))

We are basically telling Python to:

Telnet on 192.168.146.132
Prompt for Username
Prompt to type login password and also ensure that the typed characters are not displayed on the screen as we have used getpass module.
As soon as we se R1> on the screen, we will execute “enable” command which should prompt to enter enable password.
The python script then executes “conf t” and goes to global configuration mode
Then it executes “interface loop 0“
Then it executes “ip address 8.8.8.8 255.255.255.0“
Then it executes “no shutdown“
Then it executes “end“
Then it executes “show ip interface brief“
Then it exits
Then it prints the output.

Here is the output of the Python script execution:

Here is python script to run loop/repeated tasks on a single switch/router

import getpass
import telnetlib

HOST = "192.168.146.137"
user = input('Enter your telnet username please: ')
password = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until(b'Username: ')
tn.write(user.encode('ascii') + b'\n')
if password:
    tn.read_until(b'Password: ')
    tn.write(password.encode('ascii') + b'\n')

tn.write(b"enable\n")
tn.write(b"cisco\n")
tn.write(b"conf t\n")

for n in range (2,101):
    tn.write(b"vlan " + str(n).encode('ascii') + b"\n")
    tn.write(b"name Users_Vlan_" + str(n).encode('ascii') + b"\n")

tn.write(b"end\n")
tn.write(b"exit\n")
print(tn.read_all().decode('ascii'))

Here is python script to run loop/repeated tasks on a several switches/routers

import getpass
import telnetlib

HOST = "localhost"
user = input('Enter your telnet username please: ')
password = getpass.getpass()

f = open ('myswitches')

for IP in f:
    IP=IP.strip()
    print ('Configuring vlans on switch ' + (IP))
    HOST = IP
    tn = telnetlib.Telnet(HOST)
    tn.read_until(b'Username: ')
    tn.write(user.encode('ascii') + b'\n')
    if password:
       tn.read_until(b'Password: ')
       tn.write(password.encode('ascii') + b'\n')

    tn.write(b"conf t\n")

    for n in range (2,101):
       tn.write(b"vlan " + str(n).encode('ascii') + b"\n")
       tn.write(b"name Users_Vlan_" + str(n).encode('ascii') + b"\n")

    tn.write(b"end\n")
    tn.write(b'exit\n')
    print(tn.read_all().decode('ascii'))

Here is python script to run several tasks on several Switches & Routers

import getpass
import telnetlib

HOST = "localhost"
user = input('Enter your telnet username please: ')
password = getpass.getpass()

f = open ('myswitches')

for IP in f:
    IP=IP.strip()
    print ('Configuring vlans on switch ' + (IP))
    HOST = IP
    tn = telnetlib.Telnet(HOST)
    tn.read_until(b'Username: ')
    tn.write(user.encode('ascii') + b'\n')
    if password:
       tn.read_until(b'Password: ')
       tn.write(password.encode('ascii') + b'\n')
    tn.write(b"conf t\n")
    tn.write(b"vlan 2\n")
    tn.write(b"name Second\n")
    tn.write(b"exit\n")
    tn.write(b"vlan 3\n")
    tn.write(b"name Third\n")
    tn.write(b"exit\n")
    tn.write(b"vlan 4\n")
    tn.write(b"name Fourth\n")
    tn.write(b"exit\n")
    tn.write(b"vlan 5\n")
    tn.write(b"name Fifth\n")
    tn.write(b"end\n")
    tn.write(b'exit\n')
    print(tn.read_all().decode('ascii'))

Here is python script to run backup configuration on Switches & Routers and the ‘myswitches‘ file

#backup configuration file
import getpass
import telnetlib

user = input('Enter your telnet username please: ')
password = getpass.getpass()

f = open ('myswitches')

for IP in f:
    IP=IP.strip()
    print ('Get the running configuration from switch ' + (IP))
    HOST = IP
    tn = telnetlib.Telnet(HOST)
    tn.read_until(b'Username: ')
    tn.write(user.encode('ascii') + b"\n")
    if password:
        tn.read_until(b'Password: ')
        tn.write(password.encode('ascii') + b'\n')
    tn.write(b"terminal length 0\n")
    tn.write(b"show run\n")
    tn.write(b'exit\n')

    readoutput = tn.read_all()
    saveoutput = open("switch" + HOST, "w")
    saveoutput.write(readoutput.decode('ascii'))
    saveoutput.write("\n")
    saveoutput.close

 #myswitches files
 192.168.146.137
 192.168.146.138
 192.168.146.139
 192.168.146.140
 192.168.146.141
 192.168.146.142
 192.168.146.143
 192.168.146.144

Let me know if you find this article useful. Do have a great day!