Set Up DHCP Server

This guide will walk you through configuring your DHCP server to provide IP addresses to your physical hosts based on their MAC address. We opt to use:

  • A static DHCP range with explicit entries for your physical hosts, that is, a specific MAC will always get a specific IP address and hostname.
  • A dynamic DHCP range for everyone else in the network, for example, the admin’s laptop.

Note

You will use dnsmasq on your bootstrap host to act as DHCP server. If you already have a DHCP server in your infrastucture, configure it accordingly.

Fast Forward

If you already have a DHCP server and configured it for your physical hosts, proceed to the What’s Next section.

What You’ll Need

  • A bootstrap host.
  • A network subnet for your physical hosts.
  • (Optional) A router, a DNS server and a domain name.

For each physical host:

  • a MAC address
  • an IP address
  • a hostname

Procedure

  1. Go to your bootstrap host and install the necessary packages, if you don’t have them already on your system:

    root@host:~# apt-get update root@host:~# apt-get install -y dnsmasq

  2. Disable DNS. Copy the following configuration snippet and paste it in /etc/dnsmasq.d/dns.conf.

    # Disable DNS Server port=0 # Listen on all interfaces bind-interfaces

  3. Configure the static DHCP range. Copy the following configuration snippet and paste it in /etc/dnsmasq.d/dhcp.conf.

    # Enable DHCP logging log-dhcp # Respond to DHCP requests for the specified network # only for specified dhcp-host entries. dhcp-range=set:nodes,192.168.2.0,static # netmask dhcp-option=tag:nodes,1,255.255.255.0 # router dhcp-option=tag:nodes,3,192.168.2.1 # dns-server dhcp-option=tag:nodes,6,192.168.2.1 # domain-name dhcp-option=tag:nodes,15,internal

    Important

    Replace the IP addresses for the subnet, netmask, router, DNS server, and the domain name based on your setup.

    See also

    Human-Readable DHCP Options for DNSMASQ.

  4. Configure the static entries. For each physical host, append /etc/dnsmasq.d/dhcp.conf with an entry that looks like the following.

    dhcp-host=set:nodes,aa:8c:dc:40:33:e1,192.168.2.51,node1,infinite

    Important

    Replace the MAC address, IP address, hostname and lease time based on your setup. Note this mapping, as you will later need the IP address of each host in order to connect to it.

  5. Optional

    Configure the dynamic DHCP range. Append /etc/dnsmasq.d/dhcp.conf with the following snippet.

    dhcp-range=set:nodes,192.168.200.0,192.168.200.250,1h

    Important

    Replace the IP range based on your setup.

  6. Restart the service:

    root@host:~# service dnsmasq restart

Verify

  1. Go to your bootstrap host and install the necessary packages, if you don’t have them already on your system:

    root@host:~# apt-get update root@host:~# apt-get install -y nmap

    Note

    For version 7.40 (Debian stretch) patch /usr/share/nmap/nselib/dhcp.lua as pointed in https://github.com/nmap/nmap/issues/1909#issuecomment-583109074.

  2. Test the DHCP service:

    root@host:~# nmap --script broadcast-dhcp-discover Pre-scan script results: | broadcast-dhcp-discover: | Response 1 of 1: | IP Offered: 192.168.2.200 | DHCP Message Type: DHCPOFFER | Server Identifier: 192.168.2.2 | IP Address Lease Time: 2m00s | Renewal Time Value: 1m00s | Rebinding Time Value: 1m45s | Broadcast Address: 192.168.2.255 | Subnet Mask: 255.255.255.0 | Domain Name Server: 192.168.2.3 | Domain Name: internal |_ Router: 192.168.2.1

    Note

    In older nmap versions the script uses a static MAC address. As such, you will get an DHCPOFFER from the dynamic range. Use nmap 7.80 and pass --script-args mac=aa:8c:dc:40:33:e1 to test the static DHCP range (see also https://github.com/nmap/nmap/issues/1838).

Summary

You have successfully configured your DHCP server.

What’s Next

The next step is to configure your TFTP server.