🚫 DHCP Not Working? 7 Fixes Every Network Engineer Should Know

🔷 Introduction

DHCP (Dynamic Host Configuration Protocol) is critical in any network. When it stops working, users can’t get IP addresses — which means no internet, no communication, and major downtime.

In this guide, we’ll go through 7 real-world fixes that every network engineer should know to quickly troubleshoot DHCP issues. DHCP not working is one of the most common network issues

📌 What You’ll Learn

• Common reasons why DHCP fails

• Step-by-step troubleshooting methods

• Practical fixes used in real environments

❌ Problem: DHCP Not Assigning IP Address

Why DHCP Server Not Assigning IP:

• “Limited connectivity”

• APIPA IP (169.254.x.x)

• No internet

👉 DHCP is likely not working.

🔧 Fix 1: Check DHCP Server Status

👉 Why:

DHCP service might be disabled.

✅ Solution:

• Ensure DHCP is enabled on the interface

• Restart DHCP service if needed

🔧 Fix 2: Verify Interface Configuration

👉 Why:

DHCP is tied to a specific interface.

✅ Solution:

• Check if DHCP is enabled on the correct interface (LAN)

• Ensure interface IP is configured correctly

🔧 Fix 3: Check IP Address Pool

👉 Why:

If IP range is exhausted → no new IP assigned

✅ Solution:

• Increase DHCP range

• Remove unused leases

🔧 Fix 4: Check Physical Connectivity

👉 Why:

No connection = no DHCP request

✅ Solution:

• Verify cables

• Check switch port status

• Ensure device is connected to correct VLAN

🔧 Fix 5: Verify VLAN Configuration

👉 Why:

Wrong VLAN = DHCP request never reaches server

✅ Solution:

• Check VLAN tagging

• Ensure DHCP server is reachable from that VLAN

🔧 Fix 6: Check Firewall Policy (FortiGate Users 🔥)

👉 Why:

Firewall may block DHCP traffic

✅ Solution:

• Allow UDP ports:

  • 67 (server)

  • 68 (client)

• Ensure proper LAN policy is configured

🔧 Fix 7: Restart Client Device

👉 Why:

Client may have cached wrong IP

✅ Solution:

💻 Windows:

ipconfig /release
ipconfig /renew

💻 Linux:

dhclient -r
dhclient

🔍 Bonus: Check DHCP Logs

👉 Logs help identify:

• Request received or not

• IP assigned or rejected

⚠️ Common Mistakes

❌ DHCP enabled on wrong interface
❌ Incorrect subnet mask
❌ NAT disabled in firewall
❌ VLAN mismatch

✅ Conclusion

DHCP issues can seem complex, but in most cases, they are caused by:

✔ Configuration errors
✔ Network misalignment
✔ Firewall restrictions

By following these 7 fixes, you can quickly diagnose and resolve DHCP problems in real-world environments.

📢 Final Thoughts

Every network engineer should master DHCP troubleshooting — it’s one of the most common and critical issues in networking.

🔗 Related Guides

• FortiGate DHCP Configuration

• VLAN Setup on Cisco Switch

• Firewall Policy Configuration