Ask Your Question

Revision history [back]

[TCP Handshake]Server respond ack only instead of syn/ack

Hi Experts

I encountered an TCP handshake issue. Client initiated SYN(No.1 & 2) to server, however server responded an ACK(No.3) not SYN/ACK, but after that the server send a SYN/ACK(No.6) back to client.

According to pcap, it seems client retransmission the SYN till it RST this handshake. But somehow, the client try to re-establish the connection, and it worked normal as SYN , SYN/ACK , ACK.

My question is,

  1. What kind of situation will cause this issue happen?
  2. During handshake phase, what will client do if he received 2 ACKs ?

More Info:

  1. The dump is captured at server side interface.
  2. pcap file : https://dsc.cloud/CloudBucket/handshake.pcap
  3. Image : https://dsc.cloud/CloudBucket/Screen-Shot-2018-09-21-at-11.44.40-AM.png

Sorry for that I don't have point to upload here

Thank you,

Tom