Troubleshooting Tip: FortiGate 50G DSL Model running FortiOS version 7.4.9 issue with DSL line

Using the FortiGate 50G-DSL might have stability problems when operating on DSL circuits. Affected units exhibit intermittent loss of DSL connectivity. Once the connection drops, the device fails to automatically re-establish the link, requiring a manual reboot to restore service. In some cases, the connection does not establish at all, even after a reboot.

This known issue ID #1199322 is fixed in the released FortiOS versions 7.4.10 and 7.6.5. It is also fixed in FortiOS 8.0.0, currently scheduled for release in March 2026.

Note: These timelines for firmware release are estimated and may be subject to change.

This behavior can be confirmed by running:

diagnose debug application dsl -1

diagnose debug enable

diagnose debug disable (disable or stop the debug)

In the output, if this issue occurs, the line highlighted in bold should appear multiple times:

xdsl_config_sync(201): Start sync, config_change=1
event_recv(105): EN7517 WAN Change:01
xdsl_config_sync(207): ret=0, intended to change dsl mode from [ITU G.993.5(G.Vectoring)] to [VDSL2]
event_recv(105): EN7517 WAN Change:40
event_recv(105): EN7517 WAN Change:01
event_recv(105): EN7517 WAN Change:40
event_recv(105): EN7517 WAN Change:01
event_recv(105): EN7517 WAN Change:80
xdsl_config_sync(201): Start sync, config_change=1
event_recv(105): EN7517 WAN Change:01
xdsl_config_sync(207): ret=0, intended to change dsl mode from [ITU G.993.5(G.Vectoring)] to [VDSL2]

The debug output above indicates the firmware's inability to stabilize the DSL mode.

To collect additional data for DSL troubleshooting, see the following article: Troubleshooting Tip: Collecting Logs and Configuration for DSL Troubleshooting with TAC.