My phone is failing to get an IP address via DHCP

My phone is failing to get an IP address via DHCP

Why a Yealink Phone Might Not Get DHCP

A Yealink (or any IP phone) uses DHCP (Dynamic Host Configuration Protocol) to automatically obtain:

  1. An IP address
  2. Subnet mask
  3. Default gateway
  4. DNS servers
  5. (Optionally) TFTP/Provisioning server via Option 66 or Option 160

If it fails to get DHCP, it will typically show “Obtaining IP address…” or “Network unavailable” indefinitely.


Common Causes:

Category Example Cause
Network Connectivity Ethernet cable unplugged, bad patch cord, or port disabled
Switch Port Configuration VLAN mismatch or access port not assigned to correct voice VLAN
DHCP Server Issue DHCP service down, pool exhausted, scope misconfigured, or IP conflicts
Power Issue PoE (Power over Ethernet) not sufficient or unstable
MAC Filtering / Security Port security or DHCP snooping blocking new devices
Phone Firmware / Config Corrupted network settings (static IP set incorrectly), firmware bug


🧰 Step-by-Step Troubleshooting Guide

Step 1: Check Physical Layer

  • Verify link light on switch and phone port.

  • If no link:

    • Try a known good cable.

    • Test another port or device (like a laptop) in the same port.

    • Check if the switch port is administratively down.

Step 2: Confirm Power

  • If using PoE, ensure the switch or injector provides power:

    • Check with another PoE device.

    • If using a power adapter, verify correct voltage (typically 5V or 12V).

  • Phones with intermittent boot loops often indicate underpowered PoE.

Step 3: Test Network Access

  • Connect a laptop to the same Ethernet port and confirm:

    • It receives a DHCP address.

    • It can ping the gateway and Internet.

  • If laptop also fails DHCP → issue is network-side.

  • If laptop succeeds → focus on phone config.

Step 4: Review VLAN Settings

  • Many VoIP deployments use Voice VLANs.

  • If the phone is expecting VLAN tag 20 but the switch port is untagged or set to another VLAN:

    • DHCP broadcast won’t reach the correct DHCP scope.

  • On the phone:

    • Press Menu > Status > Network > VLAN.

    • Temporarily disable VLAN to test on the default LAN.

  • On the switch:

    • Check show interfaces switchport or equivalent command.

    • Make sure the port is in the correct VLAN or trunk configuration.

Step 5: Check DHCP Server

  • Verify that the DHCP server (Windows, Linux, or router) is:

    • Running and reachable.

    • Has available IPs in the scope.

    • Includes correct subnet and gateway.

    • If using VLANs, ensure DHCP relay (IP helper address) is configured on the router.

Step 6: Watch DHCP Traffic

If possible:

  • Run a packet capture on the switch port or with a network tap.

  • You should see:

    1. DHCP Discover from the phone.

    2. DHCP Offer from the server.

    3. DHCP Request from the phone.

    4. DHCP ACK from the server.

  • If no discover → phone isn’t sending (hardware/config issue).

  • If discover but no offer → DHCP or VLAN issue.

  • If full handshake but still no IP → firmware bug or corruption.

  • Boot the phone and press:

    • Menu → Settings → Advanced (default PIN 0000) → Network → WAN Port

    • Make sure DHCP is selected (not static IP).

    • If static, set back to DHCP and reboot.

  • Optionally reset the phone:

    • Hold OK for 10 seconds → confirm “Reset to Factory Settings”.

Step 8: Firmware or Provisioning Server

  • Outdated or corrupted firmware can cause network negotiation failures.

  • If phone boots into a bad config via provisioning, it might have VLAN or static IP mismatched.

  • Disconnect it from provisioning temporarily and reset it manually.

Step 9: Security Mechanisms

  • Switches with DHCP Snooping, Port Security, or MAC filtering might block DHCP packets.

  • Verify the switch doesn’t limit DHCP replies to trusted ports only (common in managed networks).

  • Add the phone’s port or DHCP server interface to the trusted list.

✅ Summary of Fixes by Root Cause

Problem Solution
Bad cable or port Replace cable or use another port
VLAN mismatch Disable VLAN on phone or fix switch config
DHCP scope exhausted Add more IPs to the scope
Static IP misconfig Set phone back to DHCP
DHCP snooping blocking Trust DHCP ports
Firmware glitch Factory reset or re-flash firmware


Typical Customer Network with DHCP


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