Setup Details

Platform: Ubuntu 20.04 LTS
Software used: isc-dhcp-server, webmin
Domain: corp.zeta.tech
Realm: CORP
DHCP - Sample for Hyderabad Office
DHCP Server Locations
-Bengaluru:
  - Diamond District: Microsoft DHCP 
      - 172.16.64.51
      - 172.16.64.52
  - AMR Tech Park: isc-dhcp-server 
      - 172.25.20.27
  - Harman Office: 
-Mumbai: 
  - Plex: Microsoft DHCP 
      - 172.16.64.51
      - 172.16.64.52
-Hyderabad: 
  - My Home Twitza: isc-dhcp-server
      - 172.25.65.22 
      - 172.25.65.23
-------------------------
User Details
admin user: itadmin
Pwd: qwedsa@123

Pre-requisites

All Zeta offices will use isc-dhcp server for providing IP Addresses to the hosts connecting to LAN or wifi networks. At some places, DHCP servers are stand-alone while at some locations, dhcp services are running along with dns services on the same server

Ubuntu server 20.04 LTS, fully patched
User account with sudo access
Internet Access

Setup DHCP Server

There are two steps to setup DHCP server.

Install DHCP Server and edit the configuration file to suit zeta infrastructure
Bind interfaces that will listen to dhcp requests from hosts

Install isc-dhcp-server

For installing isc-dhcp: ssh into the dhcp server using the credentials and run the following commands

$ sudo apt update && sudo apt upgrade -y
$ sudo  apt install isc-dhcp-server

Check if the service has started.

$ sudo systemctl status isc-dhcp-server.service

If it has not, then restart the service and check the status. If it still shows as inactive, try re-starting the server, else re-install the isc-dhcp server

$ sudo systemctl restart isc-dhcp-server.service

After installing the isc-dhcp server, there is two main configuration files that need to be modified
- /etc/dhcp/dhcpd.conf
- /etc/default/isc-dhcp-server
Make changes to /etc/dhcp/dhcpd.conf. Make a copy of the original file by renaming the original file as something else as a backup in case there are any issues with the configurations

$ sudo cp -prav /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd.conf_ORG

Open /etc/dhcp/dhcpd.conf in an editor and make following changes

# option definitions common to all supported networks...
option domain-name "corp.zeta.tech";
option domain-name-servers 172.25.65.22;
default-lease-time 600;
max-lease-time 7200;

#ddns update
ddns-update-style none;

#Make this server authoritative
authoritative;

## For User LAN ##
subnet  172.25.66.0 netmask 255.255.254.0 {
         range dynamic-bootp 172.25.66.21 172.25.67.254;
         option domain-name-servers 172.25.65.20;
         option domain-search "corp.zeta.tech";
         option subnet-mask 255.255.254.0;
         option routers 172.25.66.1;
         option broadcast-address 172.25.67.255;
         default-lease-time 600;
         max-lease-time 7200;
	   #printer static ipaddress
         host hyd-printer {
                hardware ethernet c0:18:03:9b:c4:40;
                fixed-address 172.25.66.11;
                }

        host spectra-ctlr {
                hardware ethernet bc:c6:1a:01:24:97;
                fixed-address 172.25.66.14;
                }

        host cardreader {
                hardware ethernet 00:be:43:93:a1:de;
                fixed-address 172.25.66.10;
                }

        }	

## FOR WIFI ##
subnet 172.25.68.0 netmask 255.255.252.0 {
         range 172.25.68.21 172.25.71.254;
         option domain-name-servers 172.25.65.20;
         option domain-search "corp.zeta.tech";
         option subnet-mask 255.255.252.0;
         option routers 172.25.68.1;
         option broadcast-address 172.25.71.255;
         default-lease-time 600;
         max-lease-time 7200;
        }

## Server Network ##
subnet 172.25.65.0 netmask 255.255.255.0 {
        }

Save the file and exit the editor

Bind DHCP interface

For DHCP server to release IP addresses, the server needs to know on which interface it has to listen for dhcp requests. Bind the interface by modifying the file /etc/default/isc-dhcp-server file. Open the file in the editor and make the below change

# Separate multiple interfaces with spaces, e.g. "eth0 eth1".
INTERFACESv4="eth0"

In our case we have only one interface on which multiple requests are made.

Save the file and restart the isc-dhcp server

$ sudo systemctl restart isc-dhcp-server

DHCP server is now installed and configured.

Webmin Installation

Webmin is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. Webmin removes the need to manually edit Unix configuration files like /etc/passwd, and lets you manage a system from the console or remotely. Latest webmin will be installed by using the webmin repositories

Adding repository

Make a copy of the original sources.list file and then add the webmin repository -

$ sudo cp -prav /etc/apt/sources.list /etc/apt/sources.list_ORG

Add the webmin repository by opening /etc/apt/sources.list file in an editor and adding the below line at the end of the file

deb http://download.webmin.com/download/repository sarge contrib

Update and add the signing key

$ sudo apt update
$ sudo wget -q -O- http://www.webmin.com/jcameron-key.asc | sudo apt-key add

Install webmin

$ sudo apt install webmin

Start using Webmin

By default webmin gets installed listening to port 10000
Open a browser and browse https://<ip-address>:10000

Webmin is now installed

DHCP Servers in other locations

There is no difference in the configuration files of the DHCP servers in other locations except for IP address changes.
Whenever a new DHCP server needs to set up,
- copy /etc/dhcp/dhcpd.conf file to the new server,
- bind the dhcp interface by modifying /etc/default/isc-dhcp-server file
- make relevant IP address changes
The DHCP server in the new location will be ready

References