Configure Link Monitoring in Crimson to Keep your FlexEdge Cellular Modem Online – HMS Support Portal

DA50 and DA70 FlexEdge | Crimson

Purpose
Configure Crimson Link Monitoring to verify internet connectivity and automatically restart the cellular link when internet access is lost.

A cellular modem can remain registered with the cellular network and retain an IP address even when internet access is no longer working. In that condition, the modem firmware may still consider the cellular connection healthy. Link Monitoring closes this gap by periodically testing a remote online host. If the test indicates that internet connectivity has failed, Crimson can restart the link to restore the connection.

APPLICABLE PRODUCTS

• FlexEdge DA50

• FlexEdge DA70

• Crimson configurations that use a supported cellular modem interface

PRE-REQUISITES

• A DA50 or DA70 with a configured and working cellular connection.

WHY LINK MONITORING IS NEEDED

The cellular modem firmware checks conditions such as network registration and whether the modem has received an IP address. Those checks do not prove that the modem can reach the internet. A carrier, routing, or upstream connectivity issue can therefore interrupt internet access while the modem still appears connected.

When Link Monitoring is enabled, Crimson periodically sends ICMP ping requests through the interface to a defined server. A loss of the required responses causes the interface to be treated as failed. For a cellular interface, selecting Restart Link as the failure action allows Crimson to restart the modem link and attempt to restore internet access.

Important
Link Monitoring tests reachability to the configured server. Choose a stable host that is expected to respond to ICMP ping. A server that blocks or rate-limits ping can cause false failure detections.

CONFIGURE LINK MONITORING

Open the cellular modem interface

1. In Crimson, open Device Configuration.

2. Navigate to System Configuration > Network > Interfaces.

3. Select the cellular modem interface, such as Modem 1, and open the Monitoring tab.

Figure 1. Modem 1 Monitoring tab in Crimson with Link Monitoring enabled and Restart Link selected.

Configure the recommended settings

Setting	Recommended value	Purpose
Link Monitoring	ICMP Ping	Periodically tests reachability by sending ping requests.
Action on Failure	Restart Link	Restarts the cellular link when the connectivity test fails.
Test Only When Idle	Disabled	Allows monitoring to run without requiring the interface to be idle.
Test Parameters	Automatic	Uses the default test server and appropriate timing and threshold values.
Server Name	8.8.8.8 with Automatic	Remote host used for the reachability test.

You can use the Automatic test parameters as the starting configuration. Use Manual when the application requires specifically validated custom values.

HOW THE SETTINGS WORK

Property	Description
Link Monitoring	Enables or disables monitoring and selects the detection method. Current Crimson versions support ICMP Ping.
Test Parameters	Automatic uses 8.8.8.8 as the test server and supplies the remaining test values. Manual allows the values to be entered.
Server Name	Defines the DNS name or IP address that receives the ping requests. The host should reliably answer ping and be far enough away in the route to represent useful connectivity.
Test Period	Controls the time between complete test sequences.
Test Window	Controls how long each ping is allowed to wait for a response.
Test Count	Controls the number of ping packets sent during a test sequence.
Success Level	When a link is failed, the test must meet the configured success threshold before the link is restored.
Failure Level	When a link is active, failing to meet the configured response threshold causes the link to switch to failed.

Note on multi-interface routing
The Crimson manual also describes Link Monitoring as a way to identify an interface that still has a physical link but has lost upstream connectivity. In multi-interface systems, a failed interface can have its route metric increased so alternate interfaces are preferred while the route remains available when no other option exists.

ADDITIONAL INFO

• The monitoring server should be outside the local cellular connection path far enough to provide a meaningful end-to-end connectivity check.

• Automatic configuration is the recommended baseline. Use manual settings only after validating the selected server, timing, and recovery behavior for the application.

• If the application uses multiple network interfaces, apply Link Monitoring where upstream failure must influence route selection. The lowest-priority interface may not require monitoring when it serves only as the final fallback.

Need further assistance?

Submit a support ticket here: https://support.hms-networks.com/