Overview
This lecture explains how to use DNSmasq as a DHCP server, provides a walkthrough of its configuration, and reviews essential IT infrastructure network services.
Using DNSmasq as a DHCP Server
- DNSmasq can serve as a DHCP server in addition to DNS.
- A DHCP server is generally configured on a machine with a static IP address.
- The server’s network interface (e.g., eth_srv) should connect to the network to distribute DHCP.
- For the example, eth_srv is assigned the IP 192.168.1.1/24.
- eth_cli is the client interface, initially without an IP address.
- The DHCP server is configured to listen for client requests and assign IP addresses from a specific range.
Basic DNSmasq DHCP Configuration
- The
interface option sets the listening interface for DHCP queries (e.g., eth_srv).
- The
bind-interfaces option restricts DNSmasq to configured interfaces only.
- The
domain option tells clients the domain name for local queries.
- DHCP options specify the default gateway and DNS server for clients.
- The DHCP range defines which IPs can be assigned and the lease time (e.g., 12 hours).
- Avoid overlapping the server’s static IP with the DHCP range.
Running the Simulation
- Use
sudo dnsmasq -d -C dhcpconfig to start DNSmasq with the configuration.
- On another terminal, run
sudo dhclient -i eth_cli -v to simulate a DHCP client.
- The client interface (eth_cli) receives an IP address (e.g., 192.168.1.80).
- DHCP lease duration determines how long an IP is reserved for a client.
DNSmasq Output and Hostname Resolution
- DNSmasq logs DHCP packet exchanges and updates hostname mappings.
- It can act as an authoritative DNS server for locally assigned addresses.
- Hostnames assigned can be resolved via local DNS queries (e.g., with the
dig command).
Best Practices and Real-world Use
- In production, DHCP servers and clients typically run on separate devices.
- Test DHCP and DNS setups on isolated networks, never on production networks.
Key Terms & Definitions
- DHCP (Dynamic Host Configuration Protocol) — Automatically assigns IP addresses and configuration to devices on a network.
- DNSmasq — A lightweight tool providing both DNS and DHCP services.
- Lease Time — Duration an IP address is assigned to a client before expiration.
- Static IP Address — A fixed IP address manually assigned to a device.
Action Items / Next Steps
- Review the DNSmasq DHCP configuration options.
- Practice setting up a DHCP server and client on a test network.
- Read about additional DHCP options for advanced network setups.