An ACK packet got lost in a TCP three way handshake

asked 2021-11-28 15:10:22 +0000

gash gravatar image

My server sends an SYN packet and the other end(another customer server) respond with SYN-ACK but the customer server sends a re-transmition because it couldn't get the ACK packet. I have captured the packet and i can see the ACK on the server, serverfarm switch, but i couldn't see it on my ASA firewall. what could be the possible reason, any help is appriciated.

edit retag flag offensive close merge delete


Can you capture ACK packets in front of the ingress and egress ASA interfaces? This will verify if the ASA received the ACK packet and if it forwarded the ACK packet.

BigFatCat gravatar imageBigFatCat ( 2021-11-28 23:30:33 +0000 )edit

thank your for your feedback, yes I have captured both on the egress and ingress using ASDM and on both captures, ACK of the 3-way handshake is lost. one question though, when we capture on the egress side, does the firewall capture after processing or directly from the inside interface.?

gash gravatar imagegash ( 2021-11-30 05:52:00 +0000 )edit