I did a test again using NMAP. I did an aggressive scan. I have LWIP running on my board, with 3 listener open.
After the scan, i couldn't connect to board using a tcp client. I debugging the code: lwip_stats doesn't show nothing strange, driver works, all pbufs seems free.
I have a wireshark log, but it's a zip file of 4MBytes... i suppose i cannot attach here If it could be useful, i can send it to a private email of someone of active developers... please provide me the email address.
I don't know how debug this situation.... i'm trying again now.... any idea????