CentOS & Fedora DHCP Server Installation and Configuration Ansible Role

This role configures a basic DHCP server which can be used as:

• regular primary DHCP server on a local network
• or a temporary DHCP service used specifically for the purpose of allowing PXE boot clients to get temporary IP addresses while performing an unattended (or attended) CentOS & Fedora OS installation. Or other tasks that require PXE boot capabilities.

The current way it is configured in the templates/dhcpd.conf.j2 allows for both functionalities listed above. With additional custom configuration changes it can be tweaked to fit any end user needs.

To make it behave properly and not interfere with other DHCP services running on the network it can serve IP addresses to clients based on either:

• full MAC address to limit per a single device
• partial vendor specific MAC address prefix to limit to a group of devices (example: VirtualBox)
• specific string contained in the hostname

Setting the dynamic IP range in DHCP_DYNAMIC_IP_RANGE variable and client pools outside of the current DHCP range on your local network or on its own seperate VLAN will eliminate any potential conflicts even if limiting by hostname or vendor MAC address.

Note: this functionality has only been tested in a lab environment, use at your own risk in production. Actually, don't ever use this in production.

I have successfully used this in a lab environments with no conflicts with the primary DHCP service as long as the configuration is done properly and limits on MAC addresses are set carefully. Limiting the DHCP range and monitoring logs for ongoing DHCP leases helps in detecting issues quickly as well.

The worst case scenario is one of the existing clients will renew its IP address with this DHCP server. If all other network settings are the same, no issues should arrise.

Useful monitoring:

journalctl -f - watch the system log in real time, this is where client/server DHCP renewal messages will be logged.

watch -n1 "cat /var/lib/dhcpd/dhcpd.leases | grep lease - watch current list of active DHCP leases served by this server

Requirements

None.

Role Variables

Add and customize the following role variables in one of the following locations:

Recommended:

• host_vars/{{ HOSTNAME }}.yml
• group_vars/{{ GROUPNAME }}.yml

Optional:

• {{ roles_path }}/mariuszczyz.centos-dhcpd/defaults/main.yml

Repplace {{ HOSTNAME }} and {{ GROUPNAME }} with appropriate inventory names.

It's recommended to add all required variables to hosts_vars and group_vars. This way they will not get overwritten next time the original role is updated.

Variable	Comment	Example
DOMAIN_NAME	local domain name for dhcp clients	local.localdomain
DOMAIN_DNS_SERVERS	internal or public DNS servers, blank space seperated	1.1.1.1 9.9.9.9
DEFAULT_LEASE_TIME	DHCP lease time expiration in seconds	600
MAX_LEASE_TIME	max DHCP lease time expiration in seconds	7200
SUBNET_IP_ADDRESS	subnet IP address of the local network	192.168.0.0
NETMASK_IP_ADDRESS	netmask IP address of the local network	255.255.255.0
DHCP_DYNAMIC_IP_RANGE	an range of IP address to serve to clients	192.168.0.100 192.168.0.150
GATEWAY_IP_ADDRESS	local network gateway IP address	192.168.0.1
BROADCAST_IP_ADDRESS	local network broadcast IP address	192.168.1.255

Dependencies

None.

Example Playbook

Manual

Fetch this role from Ansible Galaxy manually:

ansible-galaxy install mariuszczyz.centos_dhcpd

Not Manual

Galaxy

Or include this role from Ansible Galaxy via requirements.yml

# requirements.yml
# Install from Ansible Galaxy
- src: mariuszczyz.centos_dhcpd

Github option

# requirements.yml
# Install from Github repository
- src: https://www.github.com/mariuszczyz/centos_dhcpd

Then run this to install all dependencies from Ansible Galaxy:

ansible-galaxy install -r requirements.yml

Run it

If you want to run this role individually create a new file: playbook.yml (name it however you wish btw) with the following content:

- hosts: servers
  user: YOUR USER
  become: True

  roles:
    - { role: mariuszczyz.centos_dhcpd, tags: ['centos_dhcpd'] }

Run it:

ansible-playbook -i hosts playbook.yml

License

BSD

Author Information

Author: Mariusz Czyz
Date: 12/2019
mariuszczyz.com