Troubleshooting Tip: WWAN interface does not receive DHCP IP address with auto-connect disabled after upgrade to FortiOS 7.4.7 and above

After upgrading from FortiOS 7.2 to FortiOS 7.4.7 or later, the WWAN interface may fail to obtain an IP address even when:

auto-connect is disabled
PDP-type is configured as IPv4

This issue may occur even when the configuration follows the guidance in the article below: Technical Tip: WWAN interface is down after the firmware upgrade of FortiGate.

The output of 'diagnose sys lte-modem data-session-info' may show the connection status as UNKNOWN:

LTE Modem data session information:
Interface name: wwan
IPV4 connection: QMI_WDS_CONNECTION_STATUS_UNKNOWN <-----
IPV6 connection: QMI_WDS_CONNECTION_STATUS_UNKNOWN
Profile ID: 1
Data profile name:
Profile type: QMI_WDS_PROFILE_TYPE_3GPP
PDP context type: QMI_WDS_PDP_TYPE_IPV4_OR_IPV6
APN name: xxxxxx
Auto connect: QMI_WDS_AUTOCONNECT_DISABLED
Network type: Unknown WDS Bearer Tech
Network type(last): Unknown WDS Bearer Tech

The SIM card may still receive an IP address from the carrier, as shown by:

diagnose test application lted 7
at+cgcontrdp
+CGCONTRDP: 1,5,xxxx,<IP address>
OK

This indicates the carrier assigned an IP, but it was not applied to the WWAN interface.

LTE debug logs may show that a PLMN-profile is being applied, which prevents the modem from initiating the data session.

usb_qmi_wwan_set_plmn_profile_table(749)-456: Nothing in the PLMN lock file yet.
plmn_table_check(614)-456: PLMN code entry: t-d1.de, strlen: 6   <<<
plmn_table_check(614)-456: PLMN code entry: , strlen: 0
plmn_table_check(614)-456: PLMN code entry: , strlen: 0
...
_usb_qmi_wwan_active_modem(652)-456: SIM card IMSI prefix PLMN code not allowed! Will not dial.

This prevents the WWAN interface from establishing a data connection.

In a functioning scenario, similar logs are not present, and the modem proceeds normally:

usb_qmi_wwan_set_plmn_profile_table(641)-227: Nothing in the PLMN lock file yet.
plmn_table_check(518)-227: PLMN code entry: , strlen: 0
plmn_table_check(518)-227: PLMN code entry: , strlen: 0
...
usb_qmi_wwan_start_network(267)-227: Packet data already connected!

To fix this, remove the PLMN profile and reboot the LTE modem.

To remove the PLMN-profile:

execute lte-modem PLMN-profile delete <ID>

See execute lte-modem.

To reboot the LTE-modem:

exec lte-modem cold-reboot

After the reboot, the WWAN interface should be able to obtain the IP address normally.

Related articles:

• Troubleshooting Tip: WWAN (3G/4G) interface does not obtain IP address problem 
• Technical Tip: How to check the stats for the LTE modem