1. Purpose
This document provides a structured troubleshooting procedure to diagnose and resolve situations where network clients fail to obtain an IP address from DHCP, preventing them from joining the network or accessing network resources.
The goal is to quickly identify whether the issue originates from DHCP configuration, VLAN tagging, or network broadcast propagation.
2. Scope
This SOP applies to networks where:
Pronto PC61 acts as the DHCP server
Both wired and wireless clients rely on DHCP for IP assignment
Networks are deployed in small business environments such as:
Restaurants
Retail shops
Offices
These deployments typically use simple Layer-2 network topologies with VLAN segmentation.
3. Background – DHCP Operation in Small Networks (DORA Process)
DHCP address assignment follows a four-step process known as DORA.
Step | Description |
Discover | Client broadcasts a DHCP DISCOVER message to find a DHCP server |
Offer | DHCP server (PC61) replies with a DHCP OFFER containing an available IP |
Request | Client sends DHCP REQUEST to accept the offered address |
Acknowledge | Server replies with DHCP ACK and assigns the IP address |
When DHCP Fails
If any step in the DORA sequence fails:
The client remains without an IP address
The device may show “Obtaining IP address…”
Some operating systems may assign an APIPA address (169.254.x.x)
APIPA addresses indicate DHCP failure.
4. Problem Description
Affected clients are unable to obtain a valid DHCP lease and therefore cannot communicate on the network.
Typical Symptoms
Device stuck at “Obtaining IP address…”
No valid IPv4 address assigned
Device receives APIPA address (169.254.x.x) in some cases
DHCP request/offer handshake never completes
Client cannot reach gateway or external services
5. Business Impact
DHCP failures can disrupt normal business operations.
Potential Impact
Staff devices unable to connect
Guest Wi-Fi unavailable
POS or ordering terminals lose connectivity
Service delays during peak business hours
Increased manual troubleshooting by staff
Severity depends on which VLAN or SSID is affected.
6. Common Root Causes
Root Cause | Description |
DHCP server unreachable | PC61 not receiving DHCP DISCOVER requests |
VLAN tagging issue | Client traffic placed on incorrect VLAN |
DHCP scope disabled | DHCP pool not active for that VLAN |
7. Detailed Troubleshooting Procedure
Step 1 — Confirm No DHCP Lease Received
Action
On a Windows client device, open Command Prompt and run:
ipconfig /all
Expected Problem Indicator
No valid IPv4 address assigned
Status shows “Obtaining IP address”
IP address appears as 169.254.x.x
This confirms the DHCP process has failed.
Step 2 — Verify Client Association
Ensure the client device is correctly connected.
Verify
Wireless clients connected to the correct SSID
Wired devices connected to the correct port
If the device shows connected but without an IP, continue troubleshooting.
Step 3 — Check DHCP Scope on PC61
Navigate To
Controller → Network Configuration → DHCP Settings
Verify
DHCP server enabled
Address pool configured correctly
Available free IP addresses exist
Example healthy DHCP pool:
10.10.20.10 – 10.10.20.250
Possible Issue
DHCP pool disabled
DHCP pool exhausted
If so, adjust the configuration.
Step 4 — Check VLAN Tagging / Access Port Configuration
Incorrect VLAN tagging is a common cause of DHCP failures.
Verify
Wireless networks
SSID mapped to correct VLAN
Wired networks
Switch port configured as:
Access port for correct VLAN or Native VLAN and missing tagged VLANs over Trunk/Hybrid Ports
If VLAN tags are incorrect, DHCP DISCOVER may not reach the PC61 router.
Step 5 — Inspect Intermediate Switches
If switches exist between access points and the PC61 router, verify their configuration.
Important Note
Unmanaged switches generally forward broadcasts, but they do not understand VLAN tagging.
If VLAN traffic passes through unmanaged switches:
VLAN tags may be lost, use VLAN 1 as native vlan which can be easily passed through the Unmanaged switches
DHCP traffic may reach the wrong VLAN (AP sending traffic for Vlan 10 but unmanaged switch forwarding it without tag and Router will consider traffic for Native Vlan
Recommended Solution
Use managed switches with VLAN support for segmented networks.
Using Unmanaged switch make Vlan1 only on Router using access port and use same Vlan in SSID on AP
Step 6 — Perform Packet Capture (Controller Diagnostics)
Action
Use the Pronto Controller Packet Capture tool from the tools section.
Navigate to:
Tools → Packet Capture
Capture DHCP traffic and check for the following messages:
Expected packet sequence:
Client → DHCP DISCOVER
Server → DHCP OFFER
Client → DHCP REQUEST
Server → DHCP ACK
Diagnosis
Observation | Interpretation |
No DISCOVER seen | Client broadcast not reaching network |
DISCOVER seen but no OFFER | DHCP server unreachable |
OFFER from unexpected device | Rogue DHCP server present |
7. Resolution Scenarios
Scenario A — DHCP Server Not Reachable
Symptoms
No DHCP logs recorded
No DHCP OFFER responses
Cause
DHCP DISCOVER messages not reaching PC61.
Resolution
Verify VLAN configuration
Check SSID-to-VLAN mapping
Replace unmanaged switches with VLAN-capable switches
Confirm DHCP enabled on PC61 for that VLAN
Expected Outcome
Client receives valid IP and can ping gateway.
Scenario B — DHCP Pool Exhausted or Disabled
Symptoms
PCC Controller Device page (Router) shows no available DHCP leases in DHCP section
Cause
DHCP scope too small or incorrectly configured.
Resolution
Expand DHCP pool range
Shorten DHCP lease duration
Remove stale leases
Expected Outcome
Clients receive IP addresses immediately.
9. Validation After Resolution
After applying fixes, confirm normal DHCP operation.
Verify
Client receives a valid IPv4 address
IP address belongs to the correct VLAN subnet
Client can ping the default gateway
Client can access internet resources
10. Preventive Measures
To prevent DHCP failures:
Configure VLAN tagging correctly end-to-end
Use managed switches in VLAN environments
Monitor DHCP lease availability regularly
Disable DHCP on upstream routers or modems
Reduce lease duration in high-device environments
These practices ensure reliable DHCP service.
11. Escalation Guidelines
Escalate the issue to senior networking support if:
DHCP DISCOVER packets are visible but no DHCP OFFER is generated
Multiple VLANs experience DHCP failure simultaneously
Clients continue receiving IP addresses from rogue DHCP sources
Further troubleshooting may require advanced packet analysis or network infrastructure review.