I am working with nRF54L15 running Thread CLI. The device is successfully commissioned to a Thread network and communicates through a Border Router (BR). SDK version V3.1.0
Network Setup
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PC and Thread Border Router are connected to the same router
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nRF54L15 is connected to the Thread BR
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PC acts as an IPv6 TCP server
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nRF54L15 acts as a TCP client
Observed Behavior
Using OpenThread TCP (CLI commands)
When using OpenThread TCP commands from the CLI:
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tcp init -
tcp connect -
tcp send
️ TCP connection succeeds
Data transfer works as expected
This uses the OpenThread socket API internally.
Using Zephyr BSD Sockets
When implementing the same TCP client logic using Zephyr BSD sockets, the TCP connection fails.
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Socket creation succeeds
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IPv6 address parsing succeeds
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connect()fails with errno = 116 (ETIMEDOUT)
UDP works correctly in both cases
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OpenThread UDP → works
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Zephyr BSD UDP → works
The issue occurs only for TCP over BSD sockets.
Error Details
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connect()returns< 0 -
errno = 116 (ETIMEDOUT)
Questions
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Is TCP over Zephyr BSD sockets fully supported on nRF54L15 Thread?
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Is additional Kconfig or socket offloading configuration required?
- Is there a known limitation or missing configuration for TCP over IPv6 with Thread?
int tcp_connect_test(void)
{
int sock;
struct sockaddr_in6 server;
int ret;
const char *msg = "Hello from Nordic (IPv6 TCP)\n";
char rx_buf[128];
/* Create IPv6 TCP socket */
sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
if (sock < 0) {
LOG_ERR("Socket creation failed (%d)", errno);
return -errno;
}
/* Fill server address */
memset(&server, 0, sizeof(server));
server.sin6_family = AF_INET6;
server.sin6_port = htons(SERVER_PORT);
if (inet_pton(AF_INET6, SERVER_IP6, &server.sin6_addr) != 1) {
LOG_ERR("Invalid IPv6 address");
close(sock);
return -EINVAL;
}
LOG_INF("Connecting to [%s]:%d", SERVER_IP6, SERVER_PORT);
/* Connect */
ret = connect(sock, (struct sockaddr *)&server, sizeof(server));
if (ret < 0) {
LOG_ERR("TCP connect failed (%d)", errno);
close(sock);
return -errno;
}
LOG_INF("TCP IPv6 connection SUCCESSFUL");
/* Send data */
send(sock, msg, strlen(msg), 0);
/* Receive response */
ret = recv(sock, rx_buf, sizeof(rx_buf) - 1, 0);
if (ret > 0) {
rx_buf[ret] = '\0';
LOG_INF("Received: %s", rx_buf);
}
close(sock);
return 0;
}
