Technical Tip: Understanding LTE (3G/4G) Startup Debug Messages on FortiGate

[Marit]

Description	This article explains the key debug messages generated by the FortiGate LTE module during the startup sequence, specifically, when the WWAN interface is changed from down to up and acquires an IP address via DHCP.
Scope	FortiGate 40F-3G4G v7.2.
Solution	Introduction. When troubleshooting LTE connectivity issues, it is crucial to understand the sequence of events and messages generated during the LTE interface initialization process. The debug output from the command 'diagnose debug application lted -1' provides detailed insights into this sequence. Initial Interface Configuration. Initially, the WWAN interface is administratively set to down: config system interface     edit "wwan"         set status down     next end Enabling Debug and Bringing the Interface Up. To begin monitoring the startup process: diagnose debug reset diagnose debug duration 10 diagnose debug application lted -1 diagnose debug enable config system interface     edit "wwan"         set status up     next end To disable debug: diagnose debug disable Debug Output Breakdown. After these commands, debug messages will appear in the console. Below are the key entries and their meanings: 143728.985: update_modem_status(305)-229: WWAN interface bring Up! update_modem_status 305 Meaning: The WWAN interface is being activated. 143728.994: usb_lte_probe_device(2324)-229: v:1199, p:9091, ret:15 Meaning: USB modem detected (Vendor ID: 1199, Product ID: 9091 - Sierra Wireless). 143734.282: Reg State ==> QMI_NAS_REGISTRATION_STATE_REGISTERED 143734.282: CS Attach State ==> QMI_NAS_ATTACH_STATE_ATTACHED 143734.282: PS Attach State ==> QMI_NAS_ATTACH_STATE_ATTACHED Meaning: The modem has registered with the LTE network. Both Circuit-Switched (CS) and Packet-Switched (PS) services are active. 143734.283: PLMN MCC ==> 520 143734.283: PLMN MNC ==> 4 Meaning: Connected to the network provider TrueMove (Thailand). Reference: https://mcc-mnc.org/networks. 143735.355: modem_test_cmd(2785)-229: data:|at+cpin? 143735.356: +CPIN: READY Meaning: SIM card is ready. 143743.016: sierra_qmi_wwan_check_gps_power(892)-229: GPS Antenna Power is on. 143743.016: sierra_qmi_wwan_check_modem_data_connection(772)-229 143743.113: Link Connection Status ==> QMI_WDS_CONNECTION_STATUS_DISCONNECTED Meaning: The GPS antenna is powered, but the data link is not yet established. 143746.121: Link Connection Status ==> QMI_WDS_CONNECTION_STATUS_CONNECTED 143746.503: Link Protocol ==> QMI_WDA_LINK_LAYER_PROTOCOL_RAW_IP 143746.698: PDP Type ==> QMI_WDS_PDP_TYPE_IPV4 143746.698: Primary DNS Address ==> 122.155.33.35 143746.711: Secondary DNS Address ==> 61.19.245.245 143746.711: Authentication ==> QMI_WDS_AUTHENTICATION_NONE 143746.711: IPv4 ==> 10.118.43.81 143746.711: Profile Type ==> QMI_WDS_PROFILE_TYPE_3GPP 143746.721: IPv4 Gateway ==> 10.118.43.82 143746.721: IPv4 Gateway Mask ==> 255.255.255.252 Meaning: IP session established successfully; modem has acquired DHCP lease and DNS information. 143751.465: LTE RSSI ==> -33 143751.466: LTE RSRQ ==> -8 143751.466: LTE RSRP ==> -63 143751.475: LTE SNR ==> 208 Meaning: Signal quality is strong. For reference: RSSI > -70 dBm is considered good. Lower (closer to 0) RSRQ and RSRP values generally indicate better signal quality. SNR values above 10 dB are typically good. 143749.513: TX Packets OK ==> 0 143749.513: RX Packets OK ==> 0 143813.481: TX Packets OK ==> 164 143813.495: RX Packets OK ==> 162 Meaning: Data transmission and reception began after link establishment. Notes: • The timestamp in the debug messages corresponds to the SecureCRT session log and does not reflect the internal FortiGate system clock. • This debug process is useful for identifying issues related to SIM detection, modem registration, IP assignment, or signal strength.