Justin Cooksey Codes

Cisco DHCP Pool conversion to Windows Server DHCP

Oct 13, 2024 Justin Cooksey

Well it was bound to happen! Three years now after being asked to migrate DHCP from Windows DHCP server to Cisco Routers, and automating that convertion, it's finally going back the other way.

This time the PowerShell script will read through the file (an exported Cisco Router configuration) and build the Scopes in the Windows DHCP Role. The script will need to be run on the server becoming the DHCP server for those new scopes. The user would need to have administrator privilege to allow the DHCP settings to be made.

The script follows these steps:

1. Reads through the configuration file and, using Regular Expressions, finds all DHCP Pools (Scopes), Static Assignments and Exclusions.
2. Creates all the Scopes, along with all options found under that Pool in the router configuration file.
3. Processes the Exclusions in to each Scope
4. Process all static assignments

Still a little bit in the works at the time of this posting, but testing across multiple configurations has found it working well. The Code Repository can be found on GitHub

Some DHCP Options are being handled as follows.

Example Cisco Config

ip dhcp excluded-address 10.10.0.1 10.10.1.0
ip dhcp excluded-address 10.10.3.220 10.10.3.223
ip dhcp excluded-address 192.168.0.1 192.168.0.9
!
ip dhcp pool PoolNumber1
 network 10.10.0.0 255.255.248.0
 update dns both override
 dns-server 10.10.255.1 10.10.255.2 
 domain-name domainname.local
 option 42 ip 10.10.249.11 10.10.248.11 
 default-router 10.10.0.1 
 lease 8
!
ip dhcp pool PoolNumber2
 network 192.168.0.0 255.255.255.0
 dns-server 192.168.0.10
 option 43 hex f108.0afe.0064
 default-router 192.168.0.1
!
ip dhcp pool Device1
 host 10.10.1.30 255.255.248.0
 client-identifier 01b7.37eb.1f1a.0a
 default-router 10.10.0.1 
!
ip dhcp pool Device2
 host 192.168.0.44 255.255.255.0
 client-identifier 0132.c19f.b7f3.3b

This script makes use of the IPv4Calc Module

Netbox and Ansible for for Small to Mid Business Networks

Aug 31, 2024 Justin Cooksey

Ansible and Netbox are not just for the high end data centre systems. They can also be used on networks using small to medium business switches and routers such as the Cisco SMB Product range.

Initial Auditing and OnBoarding

Initally I started with brand new empty Netbox. In which I manually created a base setup adding in each:

• Site
• Patch
• Device model in use
• Prefix, to begin with just the management subnets

Then creating a yaml file host listing to beging with, I ran an Ansible Playbook that then went through that list of devices pulling base device information:

• IP Address (Management)
• Hostname
• Model
• Serial number
• Firmware (This was not initally used)

This was then to record in to Netbox as new devices as well as exported to CSV. After I had the devices in Netbox I could do some base housekeeping and put them in the right sites, patches and rack locations.

Netbox, the Source of Truth

Once the devices were in and housekeeping done Netbox then became the Source of Truth for both our engineers and technicians and also for Ansible. I could remove the hosts yaml file an dpointing AQnsible at Netbox for its inventory I could now allow playbooks to be run against a site and other locations or across the whole group.

Minimum config

One of the frist tasks was to ensure I had all devices, configured to a standard. I hoped that they have been, but over time, without continued audits and checks, things can become a little out. So using Ansible I was able to ensure some defaults are set, such has:

• Disabling of access methods, such as HTTP, Telnet and also HTTPS
• NTP time servers and synchronised time
• Name Servers
• Monitoring service setting (SNMP)

Backup config

Another task for Ansible was to get regular configuration backups for all devices. Running an Ansible Playbook on a daily schedule (Cron) to pull the current configuration and store it on the local file system of the Ansible server. This was then replicated off site over secure protocols.

- name: Gather Facts
  gather_facts: no
  hosts: device_roles_switch
  vars:
    output_path: "{{ lookup('env', 'HOME') }}/backups/"

  tasks:
    ## Create backup folder for today
    - name: Get date stamp for filename creation
      set_fact: date="{{lookup('pipe','date +%Y%m%d')}}"
      run_once: true

    # Get Switch Config
    - name: Get Config
      community.ciscosmb.facts:
        gather_subset:
          - config

    - name: Save Config
      copy:
        content: "{{ ansible_net_config }}"
        dest: "{{ output_path }}{{ inventory_hostname }}-{{ date }}.txt"

Finding Trunks and Devices

Another task was find all the trunks between switches & patches and docuemnt them correctly in Netbox. Running an Ansible Playbook to use LLDP from gather facts to then determine th elinks between device, that could then be documented as Netbox cables. Once that was done I also used the Netbox Topology Views plugin to visualise the network.

Once that was done I could also use MAC address searches to determine what ports IP Phones, DAPs and WAPs were connected to among other devices. Since a standard brand of those was used throughout it was only a matter of searching for the manufacturer portion of the MAC address.

Windows Server DHCP conversion to Cisco CLI

Mar 4, 2021 Justin Cooksey

I recently ran in to an issue where I needed to convert a reasonably large DHCP database from a Windows Server in to a Cisco CLI to allow the Cisco to take over DHCP roles for a subnet. I found nothing that realy automated this task, even using the exported XML file. So knowing that this was the second time I needed the tool, and likely to need it again, even if it was for smaller tasks, I set about coding it in Powershell. It is the scripting system well supported in Windows land.

The current version of the script can be found on my GitHub repository: Convert-WindowsDHCPToCisco

Still ha smany DHCP options that it hasn't been setup to hanle at this point but it does follow the basic ones that most of us use.

Currently handles DHCP Options

DHCP References Used

• RFC2312
• Wikipedia DHCP Options table