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Please verify that this pcap CONFIRMS there is no OSI layer 3 issue?

Hi.

Please see attached pcap.

I'm in a classic argument as to the root cause of a failing transmission. May you please confirm (or not) that the below successful OSI layer 3 communication is evidence that this communication failure is NOT network related?

Thank you.

1 Accepted Solution

Accepted Solutions

Joseph W. Doherty
Hall of Fame
Hall of Fame

As TCP retransmissions are due to sender's TCP not getting ACKs from receiver's TCP, I would say it is a network problem, as TCP at L4, doesn't care what the app above it is.

Why is MSS 1380 in one direction and 1460 in the other direction?

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5 Replies 5

Hello,

what is the context of your question, what problems are you experiencing, and what does your topology look like ? TCP retransmissions ' occur when the sender retransmits a packet after the expiration of the acknowledgement'. The cause of this can be a lot of things, so in order to determine the root cause, we need to know what you are actually running into.

The reporter reports "lack of communication between devices." Since the 3-way handshake is complete, that means to me that the network is not the cause of the retransmissions-- it must be the server in some way. Do you agree?

My best guess is that SFTP protocol is expected by the server, but not configured on the client.

Hello,

SFTP uses port 22. Is there any indication in the Wireshark capture of traffic being sent using that port ?

application chooses port 2222 for its sftp traffic.

Joseph W. Doherty
Hall of Fame
Hall of Fame

As TCP retransmissions are due to sender's TCP not getting ACKs from receiver's TCP, I would say it is a network problem, as TCP at L4, doesn't care what the app above it is.

Why is MSS 1380 in one direction and 1460 in the other direction?

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