RE: Serial LTE modem: No DNS servers are sent to the PPP client

dejans — Thu, 17 Jul 2025 09:18:06 GMT

Hi Petr,

[quote user="Petr21"]Yes, that pull request is fixing that problem, thanks.[/quote]

This is great to hear. Thank you for the update.

Best regards,
Dejan

RE: Serial LTE modem: No DNS servers are sent to the PPP client

Petr21 — Wed, 16 Jul 2025 18:32:33 GMT

Hi,

Yes, that pull request is fixing that problem, thanks.

Petr

RE: Serial LTE modem: No DNS servers are sent to the PPP client

dejans — Wed, 16 Jul 2025 16:20:17 GMT

Hi Petr,

Please have a look at this pull request which is expected to fix DNS issue.

Best regards,
Dejan

RE: Serial LTE modem: No DNS servers are sent to the PPP client

dejans — Tue, 15 Jul 2025 08:51:30 GMT

Hi Petr,

[quote user="Petr21"]Can some engineers who are working on the Serial LTE application look into this?[/quote]

I have reached out to relevant team internally. I will try to get back to you as soon as possible, but please note that due to start of vacation period delayed replies can be expected.

Best regards,
Dejan

RE: Serial LTE modem: No DNS servers are sent to the PPP client

Petr21 — Mon, 14 Jul 2025 12:21:02 GMT

Hi,

Here is the log before those changes in that commit. You can see that the reply to the configuration request contains two DNS servers.

2025-07-14T11:44:10<dbg> net_l2_ppp: net_pkt_hexdump: 0x20095e48
                                     80 21 01 01 00 16 03 06  64 61 23 74 81 06 d9 0e |.!...... da#t....
                                     a0 82 83 06 d9 0e a4 23                          |.......#

Full log:

2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_fsm_input: (rx_q[0]): [LCP/0x20012208] LCP Configure-Req (1) id 2 payload len 0
2025-07-14T11:44:09<dbg> net_l2_ppp: fsm_recv_configure_req: (rx_q[0]): [LCP/0x20012208] Current state ACK_RECEIVED (7)
2025-07-14T11:44:09<dbg> net_l2_ppp: fsm_recv_configure_req: (rx_q[0]): [LCP/0x20012208] Sending Configure-Ack (2) id 2 to peer while in ACK_RECEIVED (7)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_send_pkt: (rx_q[0]): [LCP/0x20012208] Sending 6 bytes pkt 0x20095a08 (options len 0)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [LCP/0x20012208] state ACK_RECEIVED (7) => OPENED (9) (fsm_recv_configure_req():653)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_link_established: (rx_q[0]): [0x200121d0] Link established
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_phase_debug: (rx_q[0]): [0x200121d0] phase ESTABLISH (1) => AUTH (2) (do_auth():74)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_link_authenticated: (rx_q[0]): [0x200121d0] Link authenticated
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_phase_debug: (rx_q[0]): [0x200121d0] phase AUTH (2) => NETWORK (3) (do_network():34)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_fsm_open: (rx_q[0]): [IPCP/0x200122e0] Current state INITIAL (0)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [IPCP/0x200122e0] state INITIAL (0) => STARTING (1) (ppp_fsm_open():349)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_fsm_lower_up: (rx_q[0]): [IPCP/0x200122e0] Current state STARTING (1)
2025-07-14T11:44:09<dbg> net_l2_ppp: fsm_send_configure_req: (rx_q[0]): [IPCP/0x200122e0] Sending Configure-Req (1) id 1 to peer while in STARTING (1)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_send_pkt: (rx_q[0]): [IPCP/0x200122e0] Sending 24 bytes pkt 0x20095a4c (options len 18)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [IPCP/0x200122e0] state STARTING (1) => REQUEST_SENT (6) (ppp_fsm_lower_up():317)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_fsm_lower_up: (rx_q[0]): [PAP/0x200123b8] Current state INITIAL (0)
2025-07-14T11:44:09<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [PAP/0x200123b8] state INITIAL (0) => CLOSED (2) (ppp_fsm_lower_up():312)
2025-07-14T11:44:09<dbg> net_l2_ppp: net_pkt_hexdump: send L2
2025-07-14T11:44:09<dbg> net_l2_ppp: net_pkt_hexdump: 0x20095a08
                                     c0 21 02 02 00 04                                |.!....
2025-07-14T11:44:09<dbg> net_l2_ppp: net_pkt_hexdump: send L2
2025-07-14T11:44:09<dbg> net_l2_ppp: net_pkt_hexdump: 0x20095a4c
                                     80 21 01 01 00 16                                |.!....
2025-07-14T11:44:09<dbg> net_l2_ppp: net_pkt_hexdump: 0x20095a4c
                                     03 06 00 00 00 00 81 06  00 00 00 00 83 06 00 00 |........ ........
                                     00 00                                            |..
2025-07-14T11:44:10<inf> adc: vbat = 3594, 3v6 = 3294
2025-07-14T11:44:10<dbg> net_l2_ppp: net_pkt_hexdump: recv L2
2025-07-14T11:44:10<dbg> net_l2_ppp: net_pkt_hexdump: 0x20095e48
                                     80 21 01 01 00 16 03 06  64 61 23 74 81 06 d9 0e |.!...... da#t....
                                     a0 82 83 06 d9 0e a4 23                          |.......#

Here is the log after those changes in the commit. The Serial LTE application do not send any DNS servers in the reply, just "00"

2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: 0x20094788
                                     80 21 01 01 00 16 03 06  64 61 23 74 81 06 00 00 |.!...... da#t....
                                     00 00 83 06 00 00 00 00                          |........

Full log:

2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_fsm_input: (rx_q[0]): [LCP/0x20010b48] LCP Configure-Req (1) id 2 payload len 0
2025-07-14T11:55:15<dbg> net_l2_ppp: fsm_recv_configure_req: (rx_q[0]): [LCP/0x20010b48] Current state ACK_RECEIVED (7)
2025-07-14T11:55:15<dbg> net_l2_ppp: fsm_recv_configure_req: (rx_q[0]): [LCP/0x20010b48] Sending Configure-Ack (2) id 2 to peer while in ACK_RECEIVED (7)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_send_pkt: (rx_q[0]): [LCP/0x20010b48] Sending 6 bytes pkt 0x20094348 (options len 0)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [LCP/0x20010b48] state ACK_RECEIVED (7) => OPENED (9) (fsm_recv_configure_req():653)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_link_established: (rx_q[0]): [0x20010b10] Link established
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_phase_debug: (rx_q[0]): [0x20010b10] phase ESTABLISH (1) => AUTH (2) (do_auth():74)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_link_authenticated: (rx_q[0]): [0x20010b10] Link authenticated
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_phase_debug: (rx_q[0]): [0x20010b10] phase AUTH (2) => NETWORK (3) (do_network():34)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_fsm_open: (rx_q[0]): [IPCP/0x20010c20] Current state INITIAL (0)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [IPCP/0x20010c20] state INITIAL (0) => STARTING (1) (ppp_fsm_open():349)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_fsm_lower_up: (rx_q[0]): [IPCP/0x20010c20] Current state STARTING (1)
2025-07-14T11:55:15<dbg> net_l2_ppp: fsm_send_configure_req: (rx_q[0]): [IPCP/0x20010c20] Sending Configure-Req (1) id 1 to peer while in STARTING (1)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_send_pkt: (rx_q[0]): [IPCP/0x20010c20] Sending 24 bytes pkt 0x2009438c (options len 18)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [IPCP/0x20010c20] state STARTING (1) => REQUEST_SENT (6) (ppp_fsm_lower_up():317)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_fsm_lower_up: (rx_q[0]): [PAP/0x20010cf8] Current state INITIAL (0)
2025-07-14T11:55:15<dbg> net_l2_ppp: ppp_change_state_debug: (rx_q[0]): [PAP/0x20010cf8] state INITIAL (0) => CLOSED (2) (ppp_fsm_lower_up():312)
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: send L2
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: 0x20094348
                                     c0 21 02 02 00 04                                |.!....
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: send L2
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: 0x2009438c
                                     80 21 01 01 00 16                                |.!....
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: 0x2009438c
                                     03 06 00 00 00 00 81 06  00 00 00 00 83 06 00 00 |........ ........
                                     00 00                                            |..
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: recv L2
2025-07-14T11:55:15<dbg> net_l2_ppp: net_pkt_hexdump: 0x20094788
                                     80 21 01 01 00 16 03 06  64 61 23 74 81 06 00 00 |.!...... da#t....
                                     00 00 83 06 00 00 00 00                          |........

Can some engineers who are working on the Serial LTE application look into this?

Thanks,

Petr

RE: Serial LTE modem: No DNS servers are sent to the PPP client

dejans — Mon, 14 Jul 2025 09:40:29 GMT

Hi,

Can you share your application log? Do you see any errors which indicate that DNS information was not sent by the modem?

Best regards,
Dejan

RE: Serial LTE modem: No DNS servers are sent to the PPP client

Petr21 — Fri, 11 Jul 2025 13:15:40 GMT

Hi,

How recent have changes been made? Can you provide additional details about recent changes?

Those changes have been made in nrfconnect/sdk-nrf commit ddfb6df8ab08d034440b5792ed792f8d9c305ab3 .

https://github.com/nrfconnect/sdk-nrf/commit/ddfb6df8ab08d034440b5792ed792f8d9c305ab3

Can you specify what exactly is shown in each of 2 code blocks?

I tried to show the difference, but that wasn't a good idea, sorry. The commit is self-explanatory.

Can you provide more information about your application?

I'm using your nRF9160 with the Serial LTE modem application as an external modem controlled with the main MCU through PPP/CMUX.

Until that changes, the modem was sending the DNS server obtained from the LTE network during the PPP setup phase, but now it has stopped.

RE: Serial LTE modem: No DNS servers are sent to the PPP client

dejans — Fri, 11 Jul 2025 11:52:42 GMT

Hi,

[quote user=""]There were some recent changes in the Nordic PDN library - function pdn_dynamic_info_get that led to the changes in slm_ppp.c and the way the application gets MTU and DNS information.[/quote]

How recent have changes been made? Can you provide additional details about recent changes?

[quote user=""]Here is part of the original code and the modified code below.[/quote]

Can you specify what exactly is shown in each of 2 code blocks?

[quote user=""]Because of these changes,the application stopped sending the DNS server from the network over PPP to the client, even though it's enabled in the configuration.[/quote]

Can you provide more information about your application?

Best regards,
Dejan