W5500 vs. W5100 / W5200


I noted a different behaviour between W5500 and W5100 responding to [SYN] packet when all sockets are busy and no more connections can be accepted.
While W5100 answer with a [RST] packet, W5500 send a [RST,ACK] packet, I presume to speed up the ethernet traffic.
This difference impacts on browsers behaviour:

  • with W5100 there is a retransmission of the [SYN] packet and the request is acknowledged as soon a socket becomes available
  • with W5500 the request is aborted

Is there a way to set W5500 in order to send only the [RST] packet without the ACK as W5100 does?
I haven’t a W5200 to test. Does anybody knows how W5200 behaves?

Best regards


W5100 is implemented to send RST packet.
W5200/W5500 are implemented to send RST/ACK packet.

It is designed as hardware not software, so it cannot be changed unfortunately.

Hi hjjeon,

thanks for your answer.
Since we are tuning our project in these days and we want to use Wiznet, I think we will probably use W5100.
Could you tell me please if W5100 is a valid choice for new projects?
Or it will be discontinued soon?

Thank you very much.


W5100 is in Arduino official ethernet shield and we don’t have plan to discontinue.
But W5500 is more cheap, better performance and have 8 sockets.

So, W5500 is more suitable for web server. But if RST packet is critical issue, maybe W5100 is good choice.