What ports to forward in router?

rikytik · #1 17th Jun 03, 01:47 AM

I use Serve-U v.4 behind a Linksys router. I like to use a non standard port when serving: assume 26500, for sake of argument. In this case I would forward a range of ports in the router, say 26500-26700. In testing the setup through another ISP, the connection is registered in the Serve-U activity page, but times out on the client end because "the server didn't respond". I've tried extending the number of ports in that range, nada.

If I set DMZ on the router (forwarding all ports) it works fine--and that's what I usually end up doing for my pals on BetaONE. I've got the ftp server software configured correctly and believe the problem lies in not getting the right ports forwarded in the router.

What other range or ranges of ports need to be forwarded when using non-standard ports for serving? Ideas?

unicorn · #2 17th Jun 03, 02:15 AM

Forwarding a prot range is needed for PASV mode. The range you mantion seems a little narrow to me, but I don't know how important it is. Anyway you should forward the port the server is listening at and also the port number minus 1, in this case 26500 and 26499 (compare to port 21 and 20...), as this is how the first attempt to connect will work. Then add the needed range for PASV mode and make sure they match (settings in server and settings in router).
Hope it works...

(I have never used Serve-U, neither Linksys so the above is to be seen as a hint in general only.)

rikytik · #3 17th Jun 03, 02:41 AM

Thanks unicorn. Your mentioning that the PASV port range in the server has to match the range in the router got me thinking. I only had set the listening port. By golly I found the page where the PASV port range goes.

I'm serving a couple big iso's right now. I'll give this a test tomorrow--but that's gotta be it. I've been looking at this problem for months. Looked at that setup page a hundred times and bleeped over the 2 blank spots in the screen each time. Dummmmb. Thanks.

unicorn · #4 17th Jun 03, 03:13 AM

That's okey rikytik... Noone is dumb I think - trying to configure a ftp-server can make anyone lost. It seems as there always are a few details left to check, tick, untick, add or just fill in...
Hope it works for you when you try it out...

rikytik · #5 17th Jun 03, 01:01 PM

Hot ziggity dog. Looks like it works. I'll sleep better now.

Thanks again.

rikytik · #6 17th Jun 03, 01:45 PM

Tho I looked at help files, I even missed this.

PASV port range
When the PASV command is used Serv-U opens a data socket and tells the client where it can connect. The data socket is used for directory listings and file transfers in passive mode. By default this port range is blank which means the server will acquire a new listening socket with a random port number between 1024 and 65535 for every passive mode transfer.

Using this range Serv-U will limit which ports are used. This is very important for firewall configurations that limit incoming connections? port usage. When blank Serv-U allows Windows to pick the port number, when a range is entered Serv-U will set up a fixed number of sockets on these ports and use these to service passive mode data transfers.

If this option is used the idea is to use a range of ports that are available, i.e. above 1024, something with high port numbers like 23580-23590. The number of ports to designate depends on a few factors: If you allow FXP (direct server-to-server transfers) you need as many ports as you get concurrent FXP clients otherwise the server may not be able to figure out what passive mode connection should be routed to which FTP session. If you allow multiple connections from the same client IP you ideally need as many ports as you get concurrent connections from the same IP. This again is so Serv-U can distribute requests over the available sockets and figure out what connection should go to which session. If neither of the two applies then in theory a single port would do the job, though it is better to use at least 3 ports or so to distribute requests and make lookups faster (the lookups hook the client connection up with an FTP session). On NT/W2K a good average number would be something like 15 ports, on Win9x/ME use no more than 5 ports since that OS is 'socket challenged' and quickly runs out of available sockets. Serv-U will not allow more than 50 ports to be used for the passive mode range regardless of your settings, since that many start to impair performance. Anywhere close to 50 ports should really never be needed, even on the busiest of servers.