PASV FTP and port forwarding

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PASV FTP and port forwarding

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PASV FTP and port forwarding
PASV FTP and port forwarding
2014-05-01 08:08:35 - last edited 2021-08-21 04:09:28
Region : UnitedStates

Model : TL-ER5120

Hardware Version : V2

Firmware Version :

ISP :


I just installed a TL-ER5120 Load Balancer in which I have it configured for multiple WANS and multiple LAN connections to devices that are all on the same local network. I have a few devices on the network, including a few different servers, each of those I have assigned reserved IP's and some of those also require port forwarding.

All the port forward definitions I have made in the Advanced -> NAT -> Virtual Server section are the same as how they were assigned on my previous router. I've tested a few of those and found that some are working and some are not... In particular, I have been trying to FTP to a server that has one of these port forward definitions, where the internal port is: 21 and the external port is 11021, and the connection times out. On the other hand, if I change the external port to 21, the connection completes, and the transmission is successful. I also know that the FTP server uses port 21 for communication and ports 1024-5000 for Data transfer. The program on the internet that is attempting to access this server is using ncftp PASV commands.

I would just use a 21 -> 21 forwarding scheme, but I have multiple servers on the network that want to use that same port so I need to define the external port to something else. I have tried changing the NAPT range, thinking that perhaps that has some affect on the available FTP data port range, but have not had any success. There also seems to be a lack of documentation for what this NAPT range is for, and so I'm not sure if changing that range is the right approach anyway...

So my question is: How do I configure this Load Balancer such that I can FTP passively to the FTP server from a device on the internet? (and why doesn't the 11021 -> 21 port forwarding work when the 21 -> 21 does?)

There does not seem to be a lot of help on the internet for this, so any advice will help.
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Re:PASV FTP and port forwarding
2014-07-21 18:38:50 - last edited 2021-08-21 04:09:28
Hi, I have the exact same problem.
Any luck yet?
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Re:PASV FTP and port forwarding
2014-07-21 20:33:58 - last edited 2021-08-21 04:09:28
Found the solution:
1. setup the FTP server as passive
2. forward also port 20
3. then also forward the static port range you've setup in the FTP server
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