Routers and forwarding and FTP's, oh my

[darktubbly]

I have this Belkin Cable/DSL router. After a recent call to tech support, they said I can't run port forward an FTP server running on anything other than port 21. Apparently you have to have a router that specifically supports this feature. Any truth to this? Or was the tech in a hurry to get home?

 

[PrincessGuard]

Running an FTP server behind a router can be tricky.

An FTP server actually requires 2 ports - 21 and a randomly generated one (for PASV) or 20 (for PORT). This randomly generated port is the problem since you can't tell the router to forward a port you don't know. One way to resolve it is for the firewall to have additional software that can read/rewite the FTP commands and automatically forward the requested port. Also, depending on your FTP server, you might be able to restrict the range of the random port to a manageable size.

Your particular router may only be able to do this on port 21, so the tech might not have been wrong.

 

[darktubbly]

Ahh, gotcha. Thanks for the info!

 

[rh71]

I thought the 2nd port was always "-1" from what you set your FTP port to be... ?

I ran my FTP successfully using this concept BUT the users connecting to me needed to turn PASV mode off, IIRC.

 

[PrincessGuard]

The 2nd port is fixed on the server side in active mode. However, if the client is behind a router, active mode might not work for the same reason passive mode might not work if the server is behind a router.

Success really depends on how smart the routers are.