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A ftp client program using libcurl is getting timeout. however curl work fine to same server port running vsftpd server. Inside packet capture, difference i see that ftp client not getting new session ticket . seems like that client is waiting for that and getting timeout.

ftp client program packet captureenter image description here

curl packet capture(which work fine) enter image description here

please help in finding out cause of the issue. trying this past two days no progress.

NOTE: server is same in both cases, there is just server interfaces ip difference, which appear in packet captures.

Thanks in advance

Saurabh Singh
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  • It can be seen that the client is closing the connection 4 seconds after receiving application data from the server. The SSL handshake is finished at this stage already, so this is not a SSL problem. Session Ticket is not important here but maybe the client simply did not announce support for it. Its likely a problem in your (unknown) code. – Steffen Ullrich May 04 '21 at 06:29
  • @SteffenUllrich thanks for comment. my doubt is. is new session ticket not needed ? i feel like libcurl is waiting for that packet only. thats why when timeout happen it closes with encrypted alert. shared client ssl code work fine for https, smtps requests. seeing this on ftps requests only. ftp also work fine. – Saurabh Singh May 04 '21 at 10:11
  • The encrypted alert is likely a normal SSL shutdown, i.e. nothing special. And the SSL handshake completed successfully, no new session ticket is needed. – Steffen Ullrich May 04 '21 at 10:20
  • @SteffenUllrich why it don't need new session ticket since i don't see session reuse or anything else. – Saurabh Singh May 04 '21 at 10:57
  • and how you are sure ssl handshake is complete ? – Saurabh Singh May 04 '21 at 11:05
  • Since application data are delivered inside the connection. These are only delivered once the handshake is complete. That's how TLS works. – Steffen Ullrich May 04 '21 at 11:08

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