Port forwarded - but 'Transmission' shows it's still closed!

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Level 4

3,605 points

Port forwarded - but 'Transmission' shows it's still closed!

I'm having real issues with this one, so I thought it was time to turn to those who usually know. I have a Linksys Router connected to a Safecom Modem. I have chosen a range of ports in the router and enabled them to be forwarded. I've also made sure UPnP is enabled too. As far as the modem is concerned, all I seem to be able to do is to ensure NAT is enabled with the mode Dynamic NAPT selected also. I've gone into System Preferences/Sharing/Firewall created a new port name and opened the same range of port numbers thus letting through all TCP and UDP traffic on my chosen ports (also tried it with the Firewall off). Yet still the port remains closed and Transmission remains unable to automatically map. Any guidence would be really appreciated.

This is what it shows in Transmission's message log (if anyone can decipher it):

4/20 09:02:56 INF stopping nat-pmp
4/20 09:02:56 INF stopping upnp
4/20 09:02:58 INF starting nat-pmp
4/20 09:02:58 DBG nat-pmp create multicast socket 10
4/20 09:02:58 INF starting upnp
4/20 09:02:58 DBG sending upnp ssdp discover message
4/20 09:03:01 DBG sending upnp ssdp discover message
4/20 09:03:09 DBG sending upnp ssdp discover message
4/20 09:03:24 DBG sending upnp ssdp discover message

iMac 20", 2.1GHz, 250GB HD, 1.5GB ram, Mac OS X (10.4.9), iBook G4 1.33Ghz, Maxtor 200GB onetouch III, 6mb DSL, Linksys WRT54G wifi

Posted on Apr 20, 2007 6:30 AM

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Answer 1

Apr 20, 2007 6:47 AM in response to Simon-UK-

What port numbers? Your ISP might be blocking them at a level beyond your control.

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Answer 2

Apr 20, 2007 7:47 AM in response to Simon-UK-

Hi Simon,

You have to do the port forwarding at the router - or whatever device is the one doing NAT. Further downstream is no good.

-Phil

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Answer 3

Simon-UK- Author

Level 4

3,605 points

Apr 20, 2007 8:06 AM in response to Rich Fleming

Rich, I've chosen port numbers 55001-55010

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Answer 4

Simon-UK- Author

Level 4

3,605 points

Apr 20, 2007 8:07 AM in response to philsmith_

Phil,

The problem with my modem is that there doesn't seem to be an area set aside to port forward. I don't have the firewall active on the modem, so is there something I can alter or turn off that will at least confirm that the modem is the issue?

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Answer 5

Simon-UK- Author

Level 4

3,605 points

Apr 20, 2007 8:16 AM in response to Simon-UK-

Phil, this is all the options my modem has to offer.

User uploaded file

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Answer 6

Apr 20, 2007 9:05 AM in response to Simon-UK-

Hi Simon,

It could be under LAN configuration or maybe NAT. But the one that looks really interesting is Virtual Server. That sounds like something which might be port forwarding.

You see, a NAT routing device has two interfaces, one for the WAN and one for the LAN. The WAN interface might have an IP address like 71.146.152.150 and the LAN interface might have an address of 192.168.1.1. When packets come to the LAN interface from an address like 192.168.1.2, the NAT subsitutes 71.146.152.150 for the return address and sends them out the WAN interface. When replies come, the NAT puts the original address back in the source address and sends it out the LAN interface.

But let's say you want to ftp to 192.168.1.2 from the outside world. All you can connect to is 71.146.152.150. Not very likely that your modem has an ftp server, or that you would want it. The only possibility is to forward packets with port 21 to 192.168.1.2. So this process could possibly be called "virtual serving". So I think you should check out Virtual Server and see if it isn't really port forwarding with a fancy name.

-Phil

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Answer 7

Simon-UK- Author

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3,605 points

Apr 20, 2007 10:03 AM in response to philsmith_

I like the way you're thinking here Phil. It's not under LAN or NAT but...

This is the Virtual Server page. The only thing I'm not sure about is what could go in the private port, and I have to put something in there as it wouldn't accept an entry without it.

User uploaded file

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Answer 8

Apr 20, 2007 11:16 AM in response to Simon-UK-

Okay, we've almost got this solved. The private port is the port on which the server is listening on your Mac. Let's take the ssh protocol, for example. If your sshd is configured to listen on port 6000, then you forward port 22 to private port 6000. Most protocols will just direct the public port to the same private port. There are some security considerations, which you balance against the inconvenience. If you're setting up a web server, just forward port 80 to port 80. Since I'm not sure what you're doing, that's my best advice. Don't use telnet or ftp, use ssh or sftp instead. Use good passwords and change them often. A NAT is a great defence. Port forwarding opens it up a little. So a little caution is useful.

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Answer 9

Simon-UK- Author

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3,605 points

Apr 20, 2007 12:38 PM in response to philsmith_

Not too sure what you just said then. Basically, I'm setting up a torrent client so I need to open a suitable port. If I want to allow incoming TCP on port 55010 what do you suggest I place in the boxes?

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Answer 10

Apr 20, 2007 1:00 PM in response to Simon-UK-

All port fields should be 55010, and the ip address the address of your Mac.

I was just trying to caution you, and to make you aware that the very thing you're circumventing was your biggest safeguard from baddies on the net. Just in case you went wild and starting adding all sorts of things. I'm no security expert - maybe someone here can fill you in on security issues with torrent use?

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Answer 11

Simon-UK- Author

Level 4

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Apr 21, 2007 1:15 AM in response to philsmith_

I appreciate the words of caution Phil.

Ok. Applied the settings. Something has changed - Instead of the incoming TCP port showing closed, it's now showing 'stealth'. It's obviously made some difference - just not quite the right one. Any suggestions.

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Answer 12

jabesse

Level 1

9 points

Apr 21, 2007 1:50 AM in response to Simon-UK-

I think it's now something within Transmission. I have port forwarding setup ok, and also get the 'stealth'. Transmission seems to work ok with it.

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Answer 13

Simon-UK- Author

Level 4

3,605 points

Apr 21, 2007 2:00 AM in response to jabesse

Hi jabesse,

Yes it will work - in fact it seems to work fine even when the port is showing as closed. However, download speeds should dramatically increase if the port can be opened and more connections can be made. That's why I'm trying so hard to understand why I can't get that elusive green light.

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Answer 14

Simon-UK- Author

Level 4

3,605 points

Apr 21, 2007 6:40 AM in response to philsmith_

Well, I was even able to find a guide online to setting up port forwarding for my safecom modem. Their description matches precisely what you'd suggested to do, so why the port doesn't now show as being open instead of Stealth, I just don't know? I've even tried setting up a static IP address, but that doesn't seem to make a difference.

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Answer 15

Apr 21, 2007 8:28 AM in response to Simon-UK-

Hi Simon,

Stealth mode is good. It just means that your router won't respond to uninvited inquiries, like a ping. It's not a good idea to disable it. If you must, it would be a setting in the WAN area, I suspect.

-Phil

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