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New Member

FTP Failure: Lots of TCP Retransmission & Duplicate ACK

Hi Friends,

I am having some serious problem with FTP transfer between 2 sites. When ever trying to send files more than 10 15 Mb its failing or less files receiving.

I put a sniffer into one of access switch between and capture some data. I can see a lot of retransmissions and DUP ACK happening.

Capture File :-

Can some expert on packet capture help me understand this :-

1. Everything was fine till Line-69 i.e the ACK send from receiver( to server(

2. On Line-70 Server send a packet with SEQ-42901.

3. Next the receiver replies it with ACK-44201.

4. The server notice that the previous SEQ-42901 is not ACK, so it mentioned it as lost frame.

5. On the exact next trasmit the server directly move to a SEQ-78145 WHY ???...

6. Next there are 12 DUP-ACK on ACK-44201 from client to server and then there is a FAST Retransmision from server for that segment.

7. And further a lot of similar problems through out the capture,which is the cause of failure.

Can someone help me understanding the cause of this.

Hall of Fame Super Gold

FTP Failure: Lots of TCP Retransmission & Duplicate ACK

What is the Cisco related question in there ?

New Member

Hello,Did you find a solution


Did you find a solution to your problem ?

I am facing a similar situation and I cannot find the root cause.

Thank you

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