Telnet cisco switch using python

Question

I am telnetting to a cisco switch via python script. The code goes as follows:

#!/usr/bin/python
import getpass
import sys
import telnetlib

HOST = "10.203.4.1"
user = raw_input("Enter your remote account: ")
password = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until("login: ")
tn.write(user + "\n")
if password:
  tn.read_until("Password: ")
  tn.write(password + "\n")

tn.write("vt100\n")
tn.write("ls\n")
tn.write("exit\n")
print tn.read_all()

It just hangs up after running the script. How can I resolve this?

Answer 1

Here is a simpler solution:

import pexpect
import getpass

HOST = "10.203.4.1"
user = raw_input("Enter your remote account: ")
password = getpass.getpass()

child = pexpect.spawn ('telnet '+HOST)
child.expect ('Username: ')
child.sendline (user)
child.expect ('Password: ')
child.sendline (password)
# If the hostname of the router is set to "deep"
# then the prompt now would be "deep>"
routerHostname = "deep" #example - can be different
child.expect (routerHostname+'>')
child.sendline ('enable')

Etc.

Answer 2

You should look at Trigger: https://trigger.readthedocs.org/en/latest/

It's a automation toolkit to interact with network devices, like cisco routers/switches:

from trigger.cmds import Commando

class ShowClock(Commando):
    """Execute 'show clock' on a list of Cisco devices."""
    vendors = ['cisco']
    commands = ['show clock']

if __name__ == '__main__':
    device_list = ['foo1-abc.net.aol.com', 'foo2-xyz.net.aol.com']
    showclock = ShowClock(devices=device_list)
    showclock.run() # Commando exposes this to start the event loop

    print '\nResults:'
    print showclock.results

Check the docs for more information: https://trigger.readthedocs.org/en/latest/

Answer 3

First of all please consider using something besides telnet. SSH is a great drop in replacement. Secondly to make this pythonic use a library called pexpect to do this very thing. The last line would use the command .interact() to gain control again.

Answer 4

Cisco Python Telnet Script for cisco router and switches best and simple script for telneting and configuring layer 3 devices.

import getpass
import sys
import telnetlib

HOST = "YOUR ROUTER IP ADDRESS"
user = raw_input("Enter your telnet username: ")
password = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until("Username: ")
tn.write(user + "\n")
if password:
tn.read_until("Password: ")
tn.write(password + "\n")


 tn.write("exit\n")

  print tn.read_all()

link for the code : Download the script here

Steps:

1. An end device with installed python and connect the end device to router

2. Configure telnet and username and password database

3. Run python script

Answer 5

I wrote a similar code and got similar error. Then I made the code vocal to know where I am making mistake. What I concluded is: "Using read_all() function is not a good idea all the time. It reads infinitely and brings impression like hung mode. Try replacing it with device prompt followed by a timer during reading. And try printing it to see if code captured the desired output"

import telnetlib
import os
import sys

host = raw_input("Enter the VG IP : ")
user = "cisco"
password = "cisco"
#cmd = raw_input("Enter the command you want to feed : ")
cmd1 = "term len 0"
cmd = "show clock"
pingable = False

response = os.system("ping -c 2 " + host)
if response == 0:
    pingable = True
    print(host, "is Pingable", pingable)
else:
    print(host, "is un-Pingable", pingable)

if(pingable):
    tn = telnetlib.Telnet(host)
    banner = tn.read_until("Username:", 5)
    tn.write(user + "\n")
    print(banner)
    tn.read_until("Password:", 5)
    tn.write(password1 + "\n")
    prompt = tn.read_until("#")
    print("I am logged in\n\n")
    print(prompt)
    tn.write(cmd1 + b"\n")
    output1 = tn.read_until("#",5)
    print("my first cmd output is :", output1, "\n")
    tn.write(cmd + "\n")
    output1 = tn.read_until("#",5)
    print("My 2nd cmd is feeded here", output1)
    tn.write("show version\n")
    output1 = tn.read_until("more-- ",5)
    print("version info : ", output1)
    tn.write("exit\n")

else:
    print(host, "is unpingable")