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Sending an RST packet in reply to a SYN/ACK

Jan 19, 2011 at 8:58 AM
Edited Jan 20, 2011 at 9:12 AM

Hi Guys,

Why do my application sending an RST packet in reply to a SYN/ACK packet?

[Source IP] [Destination IP]    TCP    [source port] > [dst port] [RST] Seq=1 Win=0 Len=0

Any idea/tips/suggestions to overcome this issue?


Appreciate your help in advance.

Jan 21, 2011 at 9:31 AM

Hi techguy0727,


I'm not sure I understand your question.

Can you elaborate on what exactly happens and please give more details on the packets being sent and by whom.



Jan 22, 2011 at 5:08 PM

Hi Boaz,

Actually this is much related to the question raised by Roster67 on the topic; my application is the one who is initiating the 3-way handshake process

1. App sends SYN

2. Server/Host replies with SYN/ACK with correct sequence number and acknowledgment number.

3. Suddenly my PC sends RST immediately instead of pushing the actual ACK packet

The thing here is I'm not getting the right 3-way hand shake process as expected. Hope this would clear you.






Jan 26, 2011 at 3:27 PM

Hi techguy0727,


If your PC sends RST immediately, this has nothing to do with Pcap.Net.

Probably, your Operating System is sending RST because it is not aware of that connection.

This is an OS issue that I'm not sure how to resolve. Maybe you can disable your network driver and only keep WinPcap driver working.

Another solution is if you can send the packets spoofed with source IP that will be routed to your network card so Pcap.Net will still get it but with a source IP that is not of your computer, it might work.