1.4.1 not talking passive mode with IOT client, 1.1.0 did

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fwedemeier
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1.4.1 not talking passive mode with IOT client, 1.1.0 did

#1 Post by fwedemeier » 2022-05-22 20:43

I've been using Filezilla 1.1.0 and Bulletproof FTP servers for development and test of IOT devices that use FTP for data transfer. 1.1.0 worked fine for Active and Passive FTP. I updated Filezilla to 1.4.1 to work with the latest. Now, Active FTP (not FTPS) continues to function. With Passive, my client times out when attempting to make a data connection at the port returned by Filezilla.

First, I installed the Filezilla 3.59.0 client and used it to passively STOR files to verify my server and LAN configurations are correct, or at least acceptable, for the 1.4.1 server.

The IOT device app executes a simple USER/PASS/TYPE/CWD/PASV/STOR/QUIT sequence. This is done on a LAN using local IP addresses: No DNS, WAN routing, port forwarding, et.al. involved. The first chunk of the attachment is the client log showing a successful passive transfer using the Bulletproof server.

The second chunk of the attachment is the client log attempting the same Passive transfer with Filezilla. When Filezilla returns the 227 response to PASV, the device app creates a TCP socket, sets no options, attempts a connect(), then times out in 10 seconds.

The third chunk of the attachment is the Filezilla log. It shows the 227 being sent, then shows the session gracefully ending 10 seconds later when the device app cleans up after the attempt to connect times out.

So:
-- Filezilla client test shows the Filezilla server is configured acceptably.
-- Bulletproof server test shows the device client is performing acceptably.

Some Filezilla forum topics show entanglement between 127.0.0.1 and local IP addresses. Here's some details on the server configuration if it's relevant:

-- Server listeners set to the computer's local address 192.168.1.40, port 21.
-- Protocols settings "Connection Security" untouched from default installation.
-- "Passive mode"
-- "Use custom port range" checked, using suggested From/To.
-- Also set 10000 to 19999 to try the lower-numbered Bulletproof range. No joy.
-- "Use following host" field empty, "Use the default host" checked
-- Also tried setting the computer's local address and 127.0.0.1. No joy.
-- "Rights management" untouched.
-- "Administration" untouched.

Suggestions???
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botg
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Re: 1.4.1 not talking passive mode with IOT client, 1.1.0 did

#2 Post by botg » 2022-05-23 09:19

What do you see in your favorite network sniffer, such as Wireshark?

fwedemeier
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Re: 1.4.1 not talking passive mode with IOT client, 1.1.0 did

#3 Post by fwedemeier » 2022-05-23 18:56

Thank you for the reply!

Wireshark shows the server returning the 227 response with the port number 55,125 (14205).
- The device sends SYN to server port 14205 ~8 milliseconds later. The device window size is 5840 bytes, MSS is 1460 bytes.
- The device retransmits SYN to server port 14205 ~6 seconds later.
- The device sends FIN,ACK to server port 21 ~5 seconds later.

The Wireshark trace for a second device (different RTOS and FTP client) shows the same sequence of events, except it retransmits SYN twice before giving up. This product uses an SOC with 256 KB RAM, so it uses a 1072-byte window and a 536-byte MSS to get everything to fit in RAM..

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Re: 1.4.1 not talking passive mode with IOT client, 1.1.0 did

#4 Post by botg » 2022-05-23 21:06

Are you using any firewalls, virus scanners, VPN software and similar software on the machine hosting the server? If so, what happens if you completely uninstall such software?

fwedemeier
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Re: 1.4.1 not talking passive mode with IOT client, 1.1.0 did

#5 Post by fwedemeier » 2022-05-24 01:03

Thank you!! Problem solved.

Windows Defender was enabled as well as the router's firewall. I was not aware of the fact that it blocks on the local network as well as the public net.

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