What is DHCP?
DHCP stands for Dynamic Host Configuration Protocol and is a network protocol that automatically assigns IP addresses and network settings to devices on a network.
Thanks to DHCP, neither user nor administrator needs to perform manual IP configuration.
🎯 What exactly does DHCP do?
When a device joins the network:
- A device (e.g. laptop, printer, PLC) requests network configuration via a DHCP Discover.
- A DHCP server responds with, among other things:
- IP address
- Subnet mask
- Default gateway
- DNS servers
- The device accepts and uses these settings temporarily (via a lease).
🔧 Key DHCP components
| Element | Function |
|---|---|
| DHCP server | Provides configurations to clients |
| DHCP client | Device that automatically requests network settings |
| Lease time | The duration for which the IP address remains valid |
| Reservation | A fixed IP binding to a MAC address |
| Scope | The range of IP addresses that may be handed out |
🏭 DHCP in OT environments
- In industrial networks, static IP addressing is often standard (for stability)
- DHCP is occasionally used for temporary devices or guest access
- MAC reservation is a safe middle ground for reliable, dynamic assignment
- SCADA, PLCs and HMIs rarely use dynamic IPs during production
🔐 Security considerations
| Risk | Mitigation |
|---|---|
| Rogue DHCP server | Enable DHCP snooping on switches |
| Unwanted IP assignment | VLAN segmentation and access control |
| External access to the internal DHCP | Block broadcasts beyond the zone via a Firewall |
📌 In summary
DHCP automates the distribution of IP settings within a network. It simplifies management but requires control and protection — especially in mixed IT/OT networks.