Automating VLAN changes for ESXi Switchports in Cisco IOS.

January 29th, 2014


At the organisation I’m currently working for, we recently experienced what appears to be a common issue, VLAN’s trunked down to ESXi nodes were inconsistent.

In our DC, we’re still running the old school Cisco Catalyst switches.  If we were running a fabric, or Nexus switches we could put port profiles to action or if we lucky enough to have some equipment running Junos <3 we could be using apply-groups for this.

Being stuck with 6500′s in the DC as our L2 platform (and a VSS for the L3 MPLS PE) this is a quick little hack job to automate configuration changes across switchports in Cisco IOS based on dynamically finding ports that are matching an interface description.

In our DC, we have a bunch of switches (defined at the top of this script) and all our switchports that go to ESXi switchports that should have this template applied are matched on the interface description containing ‘ESXHOST’

This relies on the python EXScript module

Download my script here

# This script is used for updating the VLANs that are trunked down to ESX boxes.
#  It works by logging in to each switch in the DC then looking at the interfaces that have 'ESXHOST'
#  in the description.  For each of those switchports, it will run the 'alter' commands

from Exscript.Account import Account
from Exscript.protocols import SSH2
import argparse
import getopt
import getpass
import sys

#A list of the switches to interigate.  These are the switches that have ESXi hosts in them

#Commands to execute for every switchport
vlan_commands = """
  switchport trunk allowed vlan add 5,10,15,20-25,30,40,50
  switchport trunk allowed vlan add 60,69,70,100-1000

def query_yes_no(question, default="yes"):
    """Ask a yes/no question via raw_input() and return their answer.

    "question" is a string that is presented to the user.
    "default" is the presumed answer if the user just hits <Enter>.
        It must be "yes" (the default), "no" or None (meaning
        an answer is required of the user).

    The "answer" return value is one of "yes" or "no".
    valid = {"yes":True,   "y":True,  "ye":True,
             "no":False,     "n":False}
    if default == None:
        prompt = " [y/n] "
    elif default == "yes":
        prompt = " [Y/n] "
    elif default == "no":
        prompt = " [y/N] "
        raise ValueError("invalid default answer: '%s'" % default)

    while True:
        sys.stdout.write(question + prompt)
        choice = raw_input().lower()
        if default is not None and choice == '':
            return valid[default]
        elif choice in valid:
            return valid[choice]
            sys.stdout.write("Please respond with 'yes' or 'no' "\
                             "(or 'y' or 'n').\n")

def returnInterfacesFromShowDescription(text):
    Returns a LIST of interfaces from the output of 'show interface desc' from a cisco device
    return [ x.split()[0] for x in text.split("\n") ]

def genUpdateConfigForInterfaces(config, interfaces):
    Takes in a configuration block to run, a list of interfaces and generates the appropriate int range commands with the
    config block after
    updateConfig = ""
    while len(interfaces) > 0:
        updateConfig += "int range " + ",".join(interfaces[:5])
        interfaces = interfaces[5:]
        updateConfig += "\n  %s\n" % config.strip()
    return updateConfig

def updateSwitchportsWithDescription(switch, description, username, password, commands):
    Function is used to log into a switch, find all switchports that CONTAINS the description
    with each of the said switchports, it will then execute the given commands.

    switch:  Device to log into
    description:  Search string to try and find in the switchport description
    username:  Username to log into the switch with
    password:  The password to log into the switch with
    commands:  A list of commands that should be executed

    print "Working with switch: %s" % switch

    #establish a SSH connection to the host
    conn = SSH2()
    account = Account(username, password)

    #Do some pre-setup

    #Make sure we're in super user mode
    conn.execute('terminal length 0')

    #find all ports that have ESXHOST (or whatever is set in description) in the description
    conn.execute('show int desc | i %s' % description)
    ports = conn.response.strip()

    print "Ports are:"
    print ports
    portsList = returnInterfacesFromShowDescription(ports)[1:-1]

    #go into config mode and get ready to run the update commands
    #Generate a list of the update commands that should be ran
    updateCommands = genUpdateConfigForInterfaces(commands, portsList).split("\n")
    conn.execute('conf t')
    print conn.response.strip()
    print "! About to execute the following commands."
    for line in updateCommands:
        print "! " + line

    if query_yes_no('Execute Commands?', default="no"):
        #Run the set of commands given
        for command in updateCommands:
            print conn.response

        #Exit out of config mode
        print conn.response

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description="DC ESX VLAN Utility")
    parser.add_argument('--user', help='The username that should be used to log into the switches with')

    args = parser.parse_args()
    if args.user:
        username = args.user
        username = getpass.getuser()

    password = getpass.getpass()

    # Generate a list of commands
    for switch in SWITCHES:
        updateSwitchportsWithDescription(switch, 'ESXHOST', username, password, vlan_commands)

2 responses

  1. gbromley comments:

    Thanks for the script/information, I notice you are sending conn.execute(”), is there a specific reason for this?

    In some scripts I’ve developed I’m finding that to get the expected response i need to issue conn.execute(”) before issuing the cmds I’m after, otherwise I sometimes get back the output i want or null\newlines with no obvious pattern.

    Have you seen this behaviour before?

  2. scottyob comments:

    To tell you the truth, I can’t remember at all why I’ve got that there.. Possibly just from a guide I’ve read online and followed.

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