I am not able to create socket for TCP communication

RE: I am not able to create socket for TCP communication

dejans — Tue, 04 Feb 2025 12:27:47 GMT

Hi,

Thank you for the update.

Best regards,
Dejan

RE: I am not able to create socket for TCP communication

Jaroslav Havel — Mon, 03 Feb 2025 16:49:45 GMT

Thank you for your interest, I have already managed to remove the error. The problem was in the registration to the network of the communication intermediary.

Regards
Jaroslav

RE: I am not able to create socket for TCP communication

Jaroslav Havel — Mon, 03 Feb 2025 16:49:22 GMT

Thank you for your interest, I have already managed to remove the error. The problem was in the registration to the network of the communication intermediary.

Regards
Jaroslav

RE: I am not able to create socket for TCP communication

dejans — Mon, 03 Feb 2025 16:42:07 GMT

Hi,

Could you provide complete application log which shows the "Network is unreachable" error?

Best regards,
Dejan

RE: I am not able to create socket for TCP communication

Eivind J — Mon, 03 Feb 2025 14:28:18 GMT

Hi, have you made sure that the modem is connected to the network?

You can use the LTE link controller library for this, or to do it manually with use of the AT monitor library (CONFIG_AT_MONITOR=y):

K_SEM_DEFINE(cereg_sem, 0, 1);
AT_MONITOR(at_mon_cereg, "+CEREG", at_handler_cereg);

static void at_handler_cereg(const char *notif)
{
	int err;

	printk("+CEREG notification: %.*s\n", strlen(notif) - strlen("\r\n"), notif);

	if (!strncmp(notif, "+CEREG: 1", strlen("+CEREG: 1")) ||
	    !strncmp(notif, "+CEREG: 5", strlen("+CEREG: 5"))) {
	    /* Registered to home network or roaming */
		k_sem_give(&cereg_sem);
	}
}

static int network_cfun(unsigned int mode)
{
	int err;

	err = nrf_modem_at_printf("AT+CFUN=%u", mode);
	if (err) {
		printk("nrf_modem_at_printf failed, err %d\n", err);
		return err;
	}

	if (mode == 1 || mode == 21) {
		err = k_sem_take(&cereg_sem, K_MSEC(4000));
		if (err) {
			printk("Failed to register to network, err %d\n", err);
		}
	}
}

In main: 

/* Subscribe to network registration status notifications */
err = nrf_modem_at_printf("AT+CEREG=1");
if (err) {
	printk("Failed to register to network status notifications, err %d\n", err);
	return err;
}

/* Connect to network */
err = network_cfun(1);
if (err) {
	printk("Functional mode change failed, err %d\n", err);
	return err;
}

/* Create socket and connect */ 
...

RE: I am not able to create socket for TCP communication

Jaroslav Havel — Sun, 02 Feb 2025 17:45:58 GMT

Thank you for reply, now I am able to create socket 😊.

But I have another problem, if i try to connect my client to TCP server (I am able to establish connection with TCP server running on local IP using NAT, when I use Serial Console, AT command mode), using function connect I am not able to establish communication.

struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(64999);  // Port serveru
inet_pton(AF_INET, "98.58.85.213", &server_addr.sin_addr);
int sock;
sock= socket(server_addr.sin_family, SOCK_STREAM, IPPROTO_TCP);
	           if (sock < 0) 
             {
		            printk("Failed to create TCP socket, error: %d\n", errno);

	           }
             else 
             {
                printk("SOCKET created, fine\n");
                char ip_str[INET_ADDRSTRLEN];  
                inet_ntop(AF_INET, &server_addr.sin_addr, ip_str, sizeof(ip_str));
                printk("IP adress of server is: %s\n", ip_str);
                vytvoreno=true;
 

             } 
          // after creating socket with some delay
          int ret=connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr));
          if(ret==0)
          {
             printf("Podarilo se pripojit\n");
             pripojeno=true;

          }
          else
          {
              printf("Nepodarilo se pripojit: %d\n", ret);
              printf("Chyba pri vytvareni socketu: %d (%s)\n", errno, strerror(errno));

          }

I get error: 114 (Network is unreachable), but i know that is reachable, i tested this with AT commands.

Some tip what to do?

RE: I am not able to create socket for TCP communication

Eivind J — Sat, 01 Feb 2025 15:09:02 GMT

Hi,

Removing CONFIG_NET_L2_PPP=y and CONFIG_NET_DHCPV4=y should make your code compile. It is not needed to use the modem library and the nRF modem. If you need these for other reasons you can enable CONFIG_NET_NATIVE, which is disabled in your prj.conf.
The following should for instance be enough in many cases:

# Network
CONFIG_NETWORKING=y
CONFIG_NET_NATIVE=n
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_OFFLOAD=y
CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=y

# Modem library
CONFIG_NRF_MODEM_LIB=y

I don't see any immediate issues with the device tree provided. The default device tree in zephyr should also be ok. Note that if you want to add changes to the nRF916DK device tree for your specific application, you can add a device tree overlay with what you need in your application folder, in "<your_app_path>/boards/nrf9161dk_nrf9161_ns.overlay". This is done in some of the cellular samples in NCS, for instance the modem trace flash sample. With this name the file is picked up automatically by the build system.