Troubleshooting

Before troubleshooting, confirm the following baseline requirements:

If any requirements are missing or outdated, correct it before continuing.

Symptom

• “WAN Bonding not available”

• “Bonding tunnel disconnected”

• WAN Bonding dashboard missing in DRM

Possible Cause

• Service not enabled in DRM

• WAN Bonding feature disabled on the device

• License key missing (for self-hosted server option)

Verification step

• In DRM: Check that the subaccount has bonding licenses added and that bonding licenses have been assigned to correct the devices.

• In DRM: Navigate to the device's settings, and then click Network > SD-WAN > WAN Bonding to make sure the WAN bonding configuration is enabled. Refer to the WAN bonding workflow, and the step called Configure the WAN bonding settings to confirm that your settings are configured correctly.

Solution

• Enable the service in DRM if disabled.

• Sync configuration to the device.

• Add and activate the WAN Bonding license key (if using your own bonding server).

• Reboot the device after enabling the service.

Symptom

• Tunnel never connects

• DRM shows “Authentication failed” or “No bonding server connection”

Possible cause

• Incorrect username or password

• Tunnel credentials missing or mismatched

• Wrong bonding server address or port

• License not authorized for server use

Verification step

• In DRM: Navigate to the device's settings. Click Network > SD-WAN > WAN Bonding and check the following settings:

  • Server address / hostname

  • Port number (default UDP 5111 or TCP 443 if “Prefer TCP” enabled)

  • Username/password

Solution

• Re-enter correct credentials (ensure they match DRM and server).

• Confirm the server hostname/IP is reachable from each WAN interface.

• If using your own bonding server, confirm it’s running and licensed.

• If behind a firewall, allow outbound traffic on bonding ports (UDP 5111 or TCP 443).

Symptom

• Bonding tunnel repeatedly connects/disconnects

• High packet loss or missing bonding statistics

Possible cause

• Blocked or throttled UDP traffic

• NAT or firewall timeout

• Asymmetric routing

Verification step

• Ping each interface to test each interface's connectivity.

• If UDP is blocked, change the interface's Mode setting to TCP Mode. This allows bonding over port 443/TCP. See Add interfaces to the WAN bonding tunnel.

• Ping the WAN bonding server to make sure it is reachable.

Solution

• Open UDP port 5111 or TCP 443 in any firewall between the device and the bonding server.

• Enable Prefer TCP mode if your environment blocks or filters UDP.

• Ensure proper routing and DNS resolution for the bonding server.

Symptom

• Individual WAN links drop intermittently

• Bonding tunnel flaps or loses one interface randomly

Possible cause

• SureLink misconfigured or too aggressive

• Test target unreachable or incorrect

• Conflicts with bonding’s own link checks

Verification step

• Check the SureLink settings for each interface:

  • Test interval

  • Retry

  • Test type

  • Test target

See Configure SureLink tests for the interfaces participating in the WAN bonding tunnel for more information.

Solution

• Reduce SureLink test intervals to reduce false link resets.

• Use a reliable, always-on test target.

• Avoid redundant link monitoring between SureLink and bonding; let SureLink handle physical link recovery.

Symptom

• Tunnel is up but performance is poor (slow speeds, jitter, or latency)

Possible cause

• Incorrect bonding mode

• Mismatched link types (e.g., mixing LTE and satellite)

• Link congestion or asymmetric throughput

Verification step

• Make sure the Mode is set correctly for each interface type. See Add interfaces to the WAN bonding tunnel.

• Check the performance and connectivity of the cellular connection in Digi Remote Manager.

• Check the utilization, loss, and latency for each tunnel by accessing the WAN bonding server UI.

Solution

• Choose bonding mode suited to your links:

  • Speed Optimized for throughput

  • Low Latency for real-time traffic

  • Cellular Optimized to minimize data usage

• Avoid mixing links with drastically different latency.

• Verify that all interfaces have adequate signal and bandwidth.

Symptom

• Tunnel connects but data isn’t passing through

• Bonding server rejects the session

Possible cause

• Encryption mismatch between device and server

• Protocol incompatibility (UDP vs TCP)

Verification step

• Make sure the Encryption setting is configured correctly on both the device and the WAN bonding server. See Add interfaces to the WAN bonding tunnel to check this setting on the device configuration.

• If using Prefer TCP mode, confirm the bonding server supports TCP channels.

• Review device logs for mismatches in protocol or encryption failure.

Solution

• Align encryption and protocol settings on both ends.

• Use TCP fallback if UDP isn’t reliable.

• Restart the bonding service after any changes.

Symptom

• The tunnel works, but no bonding statistics or metrics display in the WAN bonding server UI.

Possible Cause

• Data stream not enabled in DRM

• Device not reporting bonding telemetry

• Bonding service not authenticated properly

Verification step

• Verify that the WAN bonding data stream is active in the WAN bonding server UI.

• Confirm the device is online and synced with Digi Remote Manager. On the main menu, click Devices. Find the device in the list. See the Status column for the firmware version running on the device. It should say Connected.

• Verify that stats are updating in real time by accessing the WAN bonding server UI.

Solutions

• Ensure the device has proper Digi Remote Manager connectivity.

• Restart the WAN bonding service on the device.

• Reapply the bonding configuration profile in Digi Remote Manager.

If the above steps don’t resolve the issue, gather the following information:

• Device model and firmware version

• WAN Bonding configuration details (modes, server type, authentication)

• System logs and bonding debug output

• DRM device ID and bonding profile name

Go to https://www.digi.com/support/contact-support. You can either call them or open a support case.