DHCP Fundamentals

DHCP Fundamentals (Dynamic Host Configuration Protocol)

DHCP automatically assigns IP addresses and network configuration (subnet mask, gateway, DNS servers) to devices when they join a network – so users don’t have to set this up manually.

The DHCP Process (DORA)

1. DISCOVER - Device broadcasts: "Is there a DHCP server?"
2. OFFER     - DHCP server replies: "Here's an available IP"
3. REQUEST   - Device says: "I'll take that IP"
4. ACK       - Server confirms: "Confirmed, it's yours for X hours"

What DHCP Provides

  • IP address (e.g., 192.168.1.105)
  • Subnet mask (e.g., 255.255.255.0)
  • Default gateway (router address)
  • DNS server addresses
  • Lease time (how long the device can keep this IP)

Why IT Support Needs This

If a device shows an IP like 169.254.x.x (APIPA), it means DHCP failed – the device couldn’t reach a DHCP server and assigned itself a fallback address. This is a common “no internet” symptom.

Useful Commands

  • Windows: ipconfig /release then ipconfig /renew
  • macOS: System Settings → Network → Renew DHCP Lease
  • Linux: sudo dhclient -r then sudo dhclient

Common Interview Talking Point

“If a laptop shows a 169.254.x.x address, I know that’s an APIPA address indicating DHCP failed – I’d check the network cable/WiFi connection, then try releasing and renewing the IP lease.”

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