SFTP initiates separate TCP session for file upload

[DanG]

Scenario:
Server: GlobalScape (configured to allow single session per user)
Client: FileZilla 3.1.5
Proto: SFTP
Problem: Logins always successful; uploads always fail

When using the FileZilla client, packet traces show one TCP session for login, then a second TCP session being initiated for the file upload. The GlobalScape server sees this as a second attempt from the same client and rejects it.

When using the Core FTP LE 2.1 client, packet traces show the same TCP session being used for login and re-used for upload. Uploads work every time.

It appears the second TCP session initiated by FileZilla for the file upload is the problem. One could argue the GlobalScape server isn't being very smart about counting concurrent clients, but because I don't have control over the server, I wonder if this is fix-able client-side.

If a single TCP session is part of the SFTP spec, then it would appear this is a FileZilla bug. If it's not part of the spec, can we get an SFTP configuration option to re-use one TCP session?

Thanks.

[botg]

Very stupid to configure a server in that way. A proper server can easily handle hundreds of users each with hundreds of connections.

[boco]

I don't know if it works for SFTP, but it's worth a try.

You need a Site Manager entry in Filezilla for this server. Then, in the 'Transfer settings' tab, limit the number of simultaneous connections to 1. But I don't know if it concerns TCP connections, also...

[DanG]

That did the trick. It re-used the same TCP socket for both logon and file transfer.

What I asked for was there all along!

Thank you, boco.