Thank you for this information. We will implement an option for this if the certification lab elevates this issue. I already studied it a bit, but I wasn't sure where I could get information that we are handling a UDP socket there. Or could I assume that it's not a TCP socket and therefore skip the RST?
I forgot to say that we have a list of open ports and we will drop all IPv4 packets in Ethernet driver layer if we don't have the destination port open. That is why there are no RST responses to the other ports. This is been done just to save resources. Br, Esa Hill -----Original Message----- From: lwip-users [mailto:lwip-users-bounces+esa.hill=wapice....@nongnu.org] On Behalf Of Simon Goldschmidt Sent: 18. huhtikuuta 2016 10:45 To: lwip-users@nongnu.org Subject: Re: [lwip-users] TCP SYN to UDP port Esa Hill wrote: > When nmap scan is executed against our device (LwIP 1.4.1), it > responds with RST for SYN even when the socket/port is listening only UDP > “connections”. > > Is this correct behavior (does some RFC say something about this?) or > should it just drop silently the SYN packet as it does for unused ports? > This came up in one certification process (they see it as a problem). Yes, this is correct behaviour. Any correct packet that does not match a pcb should be answered with RST (unless it is a RST itself). Not sending a RST in response is often done by devices to "hide" their presence, but I'm not sure this is really safer to do... Also I can't tell you right now if there is an lwIP setting to do so, but I think not. > Nmap results: > 49998/tcp filtered unknown > 49999/tcp filtered unknown > 50000/tcp closed ibm-db2 > 50001/tcp filtered unknown > 50002/tcp filtered iiimsf That's strange. You should see a RST on all ports. Unless you have a resource problem. As Sergio already said there is absolutely no interconnection between UDP and TCP. Simon _______________________________________________ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users _______________________________________________ lwip-users mailing list lwip-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/lwip-users