Python Scapy: Wait for CDP-Neighbor

After provisioning a new Cisco CSR1000V-Router this script

• waits until the router is fully deployed
• got it’s Management-IP-Address assigned via DHCP.

and returns this Management IP-Address.

1. Prepare

First, install „netaddr“-package.

• needed to check, if the management-IP of the CDP-Neighbor is in the correct IP-Subnet

C:\RH>pip install netaddr
Collecting netaddr
  Downloading https://files.pythonhosted.org/packages/ba/97/ce14451a9fd7bdb5a397abf99b24a1a6bb7a1a440b019bebd2e9a0dbec74/netaddr-0.7.19-py2.py3-none-any.whl (1.6MB)
    100% |████████████████████████████████| 1.6MB 4.0MB/s
Installing collected packages: netaddr
Successfully installed netaddr-0.7.19

2. the „wait-for-CDP“-Script

Obviously far to much hard-coded stuff, just as an example 😉 waiting for a CDP-Neighbor to appear with the following properties:

• hostname „CSR-A“
• an IP-Address within the network „192.168.56.0 /24“

at the interface

• VirtualBox Host-Only-Network

#! /usr/bin/env python

from scapy.all import *
load_contrib("cdp")

from netaddr import IPNetwork, IPAddress

# run it for max. 99 Packets
ip = "0.0.0.0"
wait_for_hostname = "CSR-A"
wait_for_host_in_network = "192.168.56.0/24"

interface="VirtualBox Host-Only Ethernet Adapter"
capturefilter="ether dst 01:00:0c:cc:cc:cc"

while not(IPAddress(ip) in IPNetwork(wait_for_host_in_network)):
  p=sniff(iface=interface, count=1, filter=capturefilter)
  pkt=p[0]
  #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?
    device=pkt["CDPMsgDeviceID"].val.decode()
    hostname=device.split(".")[0]
    #print("Hostname:",hostname)

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

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

3. Provision a new CSR1000V Router named „CSR-A“

C:\RH>CSR1000v-Virtual-Box.cmd
Enter CSR1000v Hostname:CSR-A
Virtual machine 'CSR-A' is created and registered.
UUID: 8a9c969e-3895-4a7c-9cbc-5f5551bf1b7b
Settings file: 'c:\RH\LAB\VM\CSR-A\CSR-A.vbox'
Creating ISO image at c:\RH\LAB\VM\CSR-A\config.iso, 1 Files, Size: 8,00 KB
100%
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Medium created. UUID: 55ea8df5-7e3c-4485-8e08-9302cb61a09d
Waiting for VM "CSR-A" to power on...
VM "CSR-A" has been successfully started.

4. Run the „wait-for-CDP-Neighbor“-Script

In a second CMD-Box, and… Be patient, of course.

C:\RH>python wait-for-cdpneighbor.py
192.168.56.101

5. Or store the returned IP-Address in an Shell-Variable „ROUTER-IP“/li>

   C:\RH>for /f %I in ('python wait-for-cdpneighbor.py 2^> nul') do @(set ROUTER-IP=%I)
   

6. and pass it to putty – using public-key authentication

The Public-Key for user „labuser“ is part of my baseline-config used to provision the virtual-router.

C:\RH>putty -ssh -i C:\RH\work\putty-rsa-key\labuser.ppk labuser@%ROUTER-IP%

Works, this is a nice preparation for an automated virtual ansible-lab, too!