WaitForCDPNeighbor.py enhanced: Wait for CDP Hostname with usable connected IP-Address.

The following version adds a „-c“ option: „Connected IP-Address“-Check.

  • the script exits, when the Router-VM is up and running and has an usable IP-Address

The Script still checks all CDP-Packets received at the specified Interface:

  • If the Sender has the correct „Hostname“ it reads the CDP-Management-IP-Address announced.
  • This IP-Address has to be within the IP-Range of any connected IP-Network at the specified Interface.

So it’ll be possible to establish a SSH-Session to the router-VM.

C:\> echo %VM%

C:\> python WaitForCDPNeighbor.py -n %VM% -c -i "VirtualBox Host-Only Ethernet Adapter"
#! /usr/bin/env python

# Ronald Heitmann
import argparse

from scapy.all import *

from netaddr import IPNetwork, IPAddress

from netifaces import AF_INET, AF_INET6, AF_LINK
import netifaces

# returns a list of all IP-Adresses bound to the specified Interface "if_name"
def get_connected(if_name):
  if_id = ""
  networks = []

  for i in ifaces.data.keys():
    iface = ifaces.data[i]
    wname = iface.data['name']
    if wname == if_name:
      if_id = i
      addresses = netifaces.ifaddresses(i)
      if AF_INET in addresses:
        for addr in netifaces.ifaddresses(i)[AF_INET]:
          ipnetwork = IPNetwork(addr["addr"]+"/"+addr["netmask"]).cidr
  return networks

# checks, if the IP-Address "ip" is within the subnet-range of any network contained in the list "networks"

def is_IP_connected(ip, networks):
  found = False
  ipnetwork = IPNetwork(ip).cidr

  for n in networks:
    if (ipnetwork in n):
      found = True

  return found

def main():

    # Parse CLI-Arguments
    parser = argparse.ArgumentParser(description='Wait for a CDP-Neighbor.')
    parser.add_argument("-i", "--interface", help="monitored interface", default="VirtualBox Host-Only Ethernet Adapter")
    parser.add_argument("-n", "--hostname", help="Neighbor to wait for", required=True)
    parser.add_argument("-c", "--connected", help="wait, until CDP-Neighbor announces an directly-connected IP-Address", action='store_true')
    args = parser.parse_args()

    #looking for a specific hostname
    hostname = ""
    wait_for_hostname = args.hostname

    #watching for CDP-Packets from this host on a specific interface
    #the router-IP should use a directly-connected IP-Address
    ip = ""
    wait_for_connected = args.connected
    networks = get_connected(interface)

    capturefilter="ether dst 01:00:0c:cc:cc:cc"

    while not((hostname == wait_for_hostname) and (not(wait_for_connected) or is_IP_connected(ip,networks))):
      p=sniff(iface=interface, count=1, filter=capturefilter)
      #print("Packet received",pkt.show())

      #is this a CDP-Packet containing a hostname?
      if (CDPMsgDeviceID in pkt):
        #is this the CDP-Neighbor we're looking for?

        if (hostname == wait_for_hostname):
          #is this a CDP-Packet containing a management-IP-Address?
          if (CDPAddrRecordIPv4 in pkt):
            #print("IP-Address found:",ip)

    #return the IP-Address to the calling application or the CLI
    return ip

if __name__ == "__main__":

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