Hello guys 
I'm a penetration tester and work in a security company, so for passion in DIY, in my project, i would to listen for incoming TCP-SYN packet and turn on a LED.
I've a ENC28J60 (just for reference, i've a model with 12 pin and 5v of vcc) and Arduino Uno.
I use the UIPEthernet.h library, which run smootly in all my project with TCP connection.
But for check for a TCP-SYN packet in incoming, anyone tried it before me?
thanks
There is not API way to get a reaction to a received SYN packet but there are parts in the library that are only reached if the received packet is a SYN packet, so if you modify the library you might get it to call function in the case a SYN packet is received.
I don't see a usage for this as with the exception of a SYN flood such a packet realizes a TCP connection afterwards so you can simply use the server code to check for incoming connections (without modifying the library code).
Please describe what you're trying to achieve. Your description is more the way you think it should be done. Maybe we have a better idea of how it might be realized.