Why can an FTP connection hang when reading a directory?

Question

Computer networks

Hello. I am connected to the Internet through a router, provider "Luganet". The HTTP connection is normal. When connecting to FTP servers, authorization succeeds, but directory reading hangs. Moreover, this does not happen all the time, sometimes it connects. Switching to active/passive mode does not help. Tried different programs - does not help. Tried to connect from a laptop - the result is the same. I tried to connect directly without a router - the result is the same. In technical support they said that everything is fine with them and the problems are on my side. Tell me, please, what could be the problem?

Answer 1

The reasons may be different, it is necessary to analyze each specific case. In FTP, in addition to the control connection, a data connection is established. It is possible:
1. Firewall blocks some ports
2. Data connection comes from another external address due to poor NAT implementation at the provider
3. DPI blocks data.
Try different services for determining the IP address, if they show a different IP, then the problem is 2. Otherwise, try turning off the firewalls / antiviruses on your side.

Answer 2

Are you working on a laptop? And what kind of balance do you have? Maybe 3g extra? When I set up balancing of 2 providers on the root tsiska using cef - everything worked fine, except for ftp, and the symptoms were the same. I decided then by hard-tying the connection to the desired address to 1 specific channel on the tsiska.