I have a multi-threaded FTP client which is uploading and downloading many files concurrently. One task is to download a specific file from the FTP server. On the command socket, the download is initiated. The data socket is opened and the download proceeds. At some point, the download hangs. After a timeout, my client closes the both sockets and tries again. The second attempt always succeeds. All of the other uploads and downloads go through without any problems.
I used Wireshark 1.12.1 on the client and server side. I filtered out the TCP stream of concern and attached. On the server side, I see duplicate ACKs, retransmissions and out of order packets. The last packet a RST is sent when the client closes the connection due to a timeout. (If I extend the timeout to several minutes, the download never recovers). On the client side, I only see the received packets (strange). In any case, I see that a packet is dropped.
This behavior is 100% reproducible with VPNC. I can’t reproduce the problem with Cisco AnyConnect.
-Nathan
I used Wireshark 1.12.1 on the client and server side. I filtered out the TCP stream of concern and attached. On the server side, I see duplicate ACKs, retransmissions and out of order packets. The last packet a RST is sent when the client closes the connection due to a timeout. (If I extend the timeout to several minutes, the download never recovers). On the client side, I only see the received packets (strange). In any case, I see that a packet is dropped.
This behavior is 100% reproducible with VPNC. I can’t reproduce the problem with Cisco AnyConnect.
-Nathan
Attached Files:
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Backup Client Side Filtered.pcapng (43.8 KB)
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Backup Server Side Filtered.pcapng (69.0 KB)