W5100 Server Only Sends Data After Client Sends a Byte

Projects Networking, Protocols, and Devices
1

Hello everyone,

I’m using an Arduino Mega 2560 with an Ethernet Shield W5100 running as a TCP server.

I’ve run into a strange issue that no AI or assistant has been able to help me solve so far.

Here’s what happens:
When a client connects to the server, I need the server to start sending data immediately — without the client needing to send anything first.

However, what actually happens is that the server only begins sending data after the client sends at least one byte (it can be any character, like “.” or “a”).
Only then does the server start transmitting data normally.

Is there any known solution for this?
I suspect the issue might be related to the Ethernet.h library or how it handles socket initialization on the W5100.

Any insights or suggestions would be greatly appreciated!

Thanks in advance,
Vagner Zupo

2

read the documentation of server.accept() here

https://docs.arduino.cc/libraries/ethernet/

3

Thank you so much, Juraj! I spent days trying to solve this and no artificial intelligence could fix the problem. Thanks for the tip.