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Cisco Meraki Documentation

Gathering DM Logs for Troubleshooting Cellular Issues

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What is a DM log?

A DM (Diagnostic Monitoring) log is an advanced log capturing method that allows us to capture and review information exchanges over the cellular network between User Equipment (UE), like the modem in an MG/MX/Z device, and the cellular tower and/or provider network. It can be thought of as similar to a wireless PCAP, in that they can be used to directly view information exchanges between the integrated modem and cellular service provider over the cellular network for troubleshooting.

DM Logging is not supported on MX67C, MX68C, Z3C, and MG21.

How are DM logs used?

DM logs are used to troubleshoot LTE/5G connectivity issues when we require additional visibility into the exchanges happening between the integrated modem and tower/provider, such as the full details of the LTE/5G Attach exchange and data session management. 

DM logs can also be used to help determine if an issue is stemming from a device firmware issue, an issue with the integrated hardware modem itself, or somewhere upstream on the cellular provider network side. 

Tips for Successful DM Log Captures

NOTE: It is easiest to effectively capture DM logs when only a single SIM is inserted. If working with multiple SIMs, be sure to disable auto-failover before testing to ensure the correct SIM is being used.  

  1. Like a PCAP, DM logging will only capture traffic/exchanges that are happening when the DM capture is running. This means for us to troubleshoot an LTE attach, we need to be running the DM log capture tool while the LTE attach is actively being negotiated by the integrated modem and demonstrating the issue. 
  2. Remember to use an appropriate filter for the capture if necessary. DM logs will automatically roll over and overwrite the oldest log after reaching 100MB of logging. With an unfiltered capture all cellular management traffic as well as IP traffic is captured, meaning the captured logging can begin to overwrite in as little as 30-60 seconds depending on the amount of data being exchanged over cellular.
  3. A device with an available wired uplink will generate less cellular traffic than a device actively using the cellular uplink for all communication.

Capturing DM Logs

BE AWARE:  Only the most recent DM log capture will be saved. 
Starting a new capture will overwrite/delete any previously existing captures.

Only run the capture for as long as needed to capture the traffic in question. DM logs will automatically roll over and overwrite the oldest log after reaching 100MB of logging.

There are several aspects that should be double checked before beginning a DM log capture:

  1. Confirm the correct SIM details/configuration
  2. Confirm the appropriate capture filter
  3. Confirm the stop parameters (manual stop, time stop, state change)

DM log filters

Using a filter will ensure only specific traffic types are captured, producing smaller captures that can be run longer before rolling over. The default capture filters available include:

  • NAS_RRC_QMI_5_1_310.dmc  (Recommended) 
    • This is the recommended filter for most situations that will require DM logging as it will only capture cellular/modem management traffic. Typically the best option for troubleshooting general cellular connectivity.
    NAS_RRC_QMI_IP_5_1_310.dmc
    • Best for troubleshooting data flows on an otherwise working connection. This filter captures both the cellular/modem management traffic as well as IP traffic passing over the link. Captures less than the Default filter but potentially much more than just the NAS_RRC_QMI filter.  
  • Default_5_1_310.dmc
    • This is the default capture filter that will capture nearly all data including management and IP traffic. Fills up quickly.

Via the Local Status Page

MX 18.210 / MG 3.201 and newer

The majority of issues involving DM logs require capturing the initial Cellular Attach sequence to troubleshoot. The following section is written with the expectation of capturing the Cellular Attach sequence and will restart the cellular connecting during this process to capture that exchange.
If you are working with an issue that requires the DM log be taken without restarting the connection, use the Start button instead of Capture DM Logging with initial Attach.

  1. Access the Local Status Page and navigate to the Configure Tab.
  2. Verify the SIM and APN configurations are correct to (re)produce the necessary behavior. 
  3. Launch the DM Logging tool
  4. Select the appropriate stop conditions and capture filter.
    • Recommended: Auto Stop after 60 seconds w/ NAS_RRC_QMI_5_1_310.dmc
  5. Click the Capture DM Logging with initial Attach button and wait for the DM capture to complete. 
  6. Download the DM log + Support Data Bundle from the Local Status Page when ready.

Before MX 18.210 / MG 3.201

Whenever possible it is recommended to upgrade to at least MX 18.210 / MG 3.201 firmware to allow the use of the Capture DM Logging with initial Attach button (above), which eliminates the need for many of the manual actions here that were required prior to MX 18.210 / MG 3.201.

Using a default APN
  1. Access the Local Status Page and navigate to the Configure Tab
  2. Configure the appropriate SIM with a dummy custom APN and save the configuration. (This should bring down the cellular connection)
  3. Launch the DM log tool.
    • Recommended to open in a separate/duplicate browser tab.
  4. Select the appropriate stop conditions and capture filter.
    • Recommended: Auto Stop after 60 seconds w/ NAS_RRC_QMI_5_1_310.dmc
  5. Start the DM capture when ready.
  6. With the DM capture active, switch tabs back to the Configure tab of the Local Status Page (or close the tool interface) to change the APN configuration back to default and save the configuration. 
  7. Wait for the modem to reload the new configuration and complete the initial Cellular Attach while the DM capture is running. (Typically ~60 seconds)
  8. Switch back to (or reopen) the DM log tool and stop the DM capture, then download the DM log + Support Data Bundle from the Local Status Page when ready.
Using a custom/static APN
  1. Access the Local Status Page and navigate to the Configure Tab
  2. Change the APN override configuration of the appropriate SIM to a placeholder APN or configure the APN settings as Default and save the configuration. (This should bring down the cellular connection)
  3. Launch the DM log tool.
    • Recommended to open in a separate/duplicate browser tab.
  4. Select the appropriate stop conditions and capture filter.
    • Recommended: Auto Stop after 60 seconds w/ NAS_RRC_QMI_5_1_310.dmc
  5. Start the DM capture when ready
  6. With the DM capture active, switch tabs back to the Configure page of the Local Status Page (or close the tool interface) to change the APN configuration back to the correct custom/static and save the configuration. 
  7. Wait for the modem to reload the new configuration and complete the Cellular Attach while the DM capture is running. (Typically ~60 seconds)
  8. Switch back to (or reopen) the DM log tool and stop the DM capture, then download the DM log + Support Data Bundle from the Local Status Page when ready.

 

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