Stubborn DHCP Leases on Netgear RAX56U with a Step by Step Fix

Stubborn DHCP Leases on Netgear RAX56U with a Step by Step Fix

Why DHCP Leases Get Stuck

A DHCP lease is a temporary permission a router gives a device to use a specific IP address. On a Netgear RAX56U, the DHCP server keeps a table of all leases, mapping MAC addresses to IPs and recording the lease start and expiration times. When a device requests an address, the router checks the table and either hands back an existing lease or assigns a new one.

Sometimes the lease table becomes corrupt or a device ends up with a duplicate IP. The result is intermittent connectivity, slow network performance, or a device that simply never gets an address. The culprit is usually not the device itself but a stale entry in the router’s DHCP cache. Fixing the issue is often a matter of clearing the stale data and letting the server rebuild the table from scratch.

Preparing to Fix the Lease Problem

Before you start fiddling with settings, take a few safety steps:

• Back up the router configuration.
  Go to Advanced → Administration → Backup and save the file to your computer. If anything goes wrong you can restore the exact state of your network.

• Check the firmware version.
  Outdated firmware can contain bugs that affect DHCP. Navigate to Advanced → Administration → Firmware Update and install any available updates.

• Document existing lease entries.
  If you plan to make significant changes, note down current IP reservations, MAC addresses, and any static mappings. You can export the lease list by clicking View DHCP Clients and copying the table into a spreadsheet.

Identifying Problematic Leases

1. Open the DHCP Client List
   Go to Advanced → LAN → DHCP Server → View DHCP Clients.
   Here you’ll see a table of all devices that have requested an address:
   MAC address | IP address | Hostname | Lease Time | Status

2. Look for anomalies

   • Duplicate IPs: Two rows with the same IP but different MACs.
   • Unusual hostnames: A device named “Unknown” or a long alphanumeric string.
   • Very long lease times that have not expired.

3. Mark the offending rows
   Note the MAC address and IP of any problematic entry. You will need this later when you reset or delete the lease.

Clearing the DHCP Lease Table

Once you have identified the entries that are causing trouble, you can begin clearing the table. The Netgear web interface does not provide a “Clear All Leases” button, but there are several ways to force the server to drop its memory.

1. Toggle the DHCP Server Off and On

• Go to Advanced → LAN → DHCP Server.
• Toggle Enable DHCP to Off.
• Wait about 30 seconds, then toggle it back to On.
• This forces the server to flush its cache.

Tip: If you have static reservations, remember to re‑enable them after you toggle the server back on.

2. Release the Lease from the Client

If a specific device is stuck with a wrong address, you can release its lease directly:

• On the device, open a terminal or command prompt.
  Windows: ipconfig /release then ipconfig /renew
  macOS/Linux: sudo dhclient -r then sudo dhclient
• The device will request a new address from the router, triggering the DHCP server to drop the old mapping.

3. Reset the DHCP Database via SSH (Advanced)

If the above steps don’t work, you can reset the internal DHCP database using the router’s shell:

1. Enable SSH under Advanced → Administration → Enable SSH.
2. Connect using an SSH client (PuTTY, OpenSSH).
3. Log in with your admin username and password.
4. Run the following commands:

cd /tmp
rm -rf dhcp

5. Restart the DHCP service:

service dhcpd restart

Warning: This method is for advanced users. Incorrect commands may corrupt the router’s configuration. Always keep a backup before attempting.

Removing Conflicting Static Reservations

Static DHCP reservations can conflict with dynamically assigned leases, especially if the reserved IP range overlaps the pool. To resolve this:

1. Go to Advanced → LAN → DHCP Server → Static DHCP.
2. Review each reservation.
3. Delete any that are no longer in use or that may clash with the pool.
4. Save the changes and reboot the router.

Checking for MAC Address Conflicts

Some routers have a MAC binding feature that forces a device to keep the same IP. If a device’s MAC changes (e.g., due to a hardware upgrade or a new network card), the binding can block a new lease.

• Go to Advanced → LAN → MAC Filtering.
• Disable the filter or remove the specific MAC entry that is causing trouble.
• Save and reboot.

Power Cycling the Router

Sometimes a simple reboot is enough to clear residual caches:

1. Power off the Netgear RAX56U.
2. Wait 30 seconds.
3. Power on and let the router fully boot (usually takes 1–2 minutes).
4. Verify that the DHCP client list is clean.

Re‑configuring the DHCP Scope

If you have repeatedly experienced lease problems, it may be time to review the DHCP scope:

1. Navigate to Advanced → LAN → DHCP Server.
2. Set the IP Address Range to a clear segment of your network (e.g., 192.168.1.100–192.168.1.200).
3. Set the Lease Time to a moderate value (e.g., 12 hours).
4. Enable Dynamic IP Address Assignment.
5. Disable IP Address Reservation unless you need specific devices to stay static.
6. Click Apply and wait for the router to apply changes.

Verifying the Fix

After performing the steps above, confirm that the DHCP server is functioning correctly:

• Check client connectivity.
  On a device, run ping 192.168.1.1 (the router’s gateway) and ping google.com to verify DNS resolution.
• Re‑view the DHCP client list.
  Make sure there are no duplicate IPs or stale entries.
• Observe lease renewals.
  Wait for the lease expiration (or manually release and renew) and ensure the device receives a fresh address without error.
• Test with multiple devices.
  Add a new laptop or phone to the network and confirm it obtains an address quickly.

What If the Problem Persists?

If after all of the above steps the router still shows stubborn leases, consider the following:

• Factory Reset
  Back up the configuration again.
  Go to Advanced → Administration → Reset to Factory Defaults.
  This wipes all settings, including DHCP reservations, and forces the router to start clean.
  After the reset, restore the backup or re‑configure from scratch.

• Contact Netgear Support
  Some firmware versions contain bugs that affect the DHCP server. Provide them with logs and the steps you have taken.

• Replace the Router
  If the hardware is older or has been subjected to heavy traffic, it may be time for a replacement. The RAX56U is still a capable model, but newer firmware or a different router may handle DHCP more gracefully.

Maintaining a Healthy DHCP Environment

• Keep firmware updated.
  New releases often fix bugs and improve DHCP stability.
• Limit the number of static reservations.
  Use them only when necessary.
• Avoid overlapping subnets.
  Ensure the DHCP range does not intersect with any manually assigned addresses.
• Monitor the client list regularly.
  Spotting anomalies early prevents prolonged downtime.

Final Thoughts

A stubborn DHCP lease can feel like a stubborn knot, but with a systematic approach you can untangle it. The Netgear RAX56U is designed to handle typical home‑office traffic, and most lease issues can be resolved by flushing the DHCP cache, removing conflicting reservations, and ensuring the firmware is current. By following the steps above you’ll reclaim a reliable, fast network that keeps your devices happily connected.