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JamTheDane
Posts: 2
Registered: ‎11-01-2009

Problem with port forwarding on a WRT120N

Hello all.

 

I just bought a WRT120N wireless router, and have run into some strange problems with port forwarding, that i cant figure out, so i hope someone here have any ideas about how to fix it.

 

I have a two router setup, because my ISP have set it up so i can only use my router from them to get my connection, and then i just have that one connected to my WRT120N. So my setup looks like the following:

 

Internet connection connect to :

 

ISPs router (Prestige 2602R-61)

IP 10.0.0.1

Set to port forward everything to 192.168.1.1 (WRT120N local IP adress)

 

This then connect to

WRT120N

Internet IP 10.0.0.2

Subnet mask 255.255.255.0

Default Gateway 10.0.0.1

Local IP adress 192.168.1.1

 

And in the WRT120N i am doing the specific port forwarding. I have forwarded the following ports and ranges to 192.168.1.100 (PCs IP adress):

4667

6112

4669

13139

3783

21

27900 to 29901

6500 to 6515

 

The problem is that ONLY the three first ports works. I have forwarded them in the exact same manner, give it a name, put in the same external and internal port, and enable the port forwarding, but according ot canyouseeme.org, only 4667, 6112, and 4669 can be seen, the rest is not responding. I even tried to enable port 21, which is a default setting in the router, but it will just not work.

 

I have of course tried to reboot both router and PC, upgraded the routers firmware, but no luck.

 

 Do anyone have any clue to what i am doing wrong? 

 

JamTheDane
Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: Problem with port forwarding on a WRT120N

1. Don't use a two router setup if possible. Use the WRT as wireless access point like this.

2. I really wonder how you can set up port forwarding to 192.168.1.1 on your ISP router. 192.168.1.1 does not exist on either side of the ISP router. It should not be possible. You have to forward the ports to the IP address of the WRT on the WAN side, i.e. to 10.0.0.2. 10.0.0.2 is the IP address of the router on the LAN side of the ISP router...

3. Please remember that port forwarding does not open a port. Setting up port forwarding only forwards ports. Nothing else. The state of the port is still determined by the state of that port on the IP to which you forward. A port will only appear open if it is forwarded to a computer on which that port is actually open.

4. In addition, please remember that testing for open UDP ports is not really possible. Do not trust test results for open/closed UDP ports.

5. For a comprehensive forwarding checklist see here.

6. Otherwise please post the output of "netstat -an" and "ipconfig /all" on that computer to which you forward. Also post the exact settings on the router for port forwarding, port triggering and DMZ host.
JamTheDane
Posts: 2
Registered: ‎11-01-2009

Re: Problem with port forwarding on a WRT120N


gv wrote:
1. Don't use a two router setup if possible. Use the WRT as wireless access point like this.

2. I really wonder how you can set up port forwarding to 192.168.1.1 on your ISP router. 192.168.1.1 does not exist on either side of the ISP router. It should not be possible. You have to forward the ports to the IP address of the WRT on the WAN side, i.e. to 10.0.0.2. 10.0.0.2 is the IP address of the router on the LAN side of the ISP router...

3. Please remember that port forwarding does not open a port. Setting up port forwarding only forwards ports. Nothing else. The state of the port is still determined by the state of that port on the IP to which you forward. A port will only appear open if it is forwarded to a computer on which that port is actually open.

4. In addition, please remember that testing for open UDP ports is not really possible. Do not trust test results for open/closed UDP ports.

5. For a comprehensive forwarding checklist see here.

6. Otherwise please post the output of "netstat -an" and "ipconfig /all" on that computer to which you forward. Also post the exact settings on the router for port forwarding, port triggering and DMZ host.

1: Good tip, that made my life a LOT easier, that was what i originally hoped to set this up as, but the Cisco tool that came with the router and configured it kept messing up, so had to do it manually, and hadnt figured out how to set it up to run like an access point :smileyhappy:.

 

 2: My bad, it was set to forward to 10.0.0.2, not to 192.168.1.1.

 

3: Everything should be open on my PC, i turned windows firewall off to make sure it was not making problems.

 

I still seems to have some issues, but that is not connected to the Cisco router, looks like my ISP router got some issues with port forwarding, i tried to remove the Cisco router and plug my PC into the ISP router, and it seems to be kinda random if a port forwarding work or not. I can open a 4 port range, and only have it report 2 of them being forwarded, when i use a canyouseeme.org or the like. My ISP cant explain why that happens either, and they are sending me a new router, so hopefully that will solve the problem, if not i might be back here later on :smileyhappy:

But your tip 1 made it a LOT easier, so hopefully i shouldnt need any more help from in here, thanks for the help.

 

JamTheDane

 

 

peanuts
Posts: 3,117
Registered: ‎09-07-2006

Re: Problem with port forwarding on a WRT120N

Expert is absolutely correct...Also try open the ports on the ISP router and check if it works or not.
nuuborigans1
Posts: 9
Registered: ‎01-30-2011

Re: Problem with port forwarding on a WRT120N

[ Edited ]

Number 4:

In addition, please remember that testing for open UDP ports is not really possible. Do not trust test results for open/closed UDP ports.

 

Question: is that true just for wrt120n model or for every cisco model?

thanks

 

*I have linkys wrt54gl and it works perfectly. this is the first I saw that! 

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: Problem with port forwarding on a WRT120N

It's true for UDP. It's UDP: it's packet-based. Unlike TCP where you have a "handshake" before you have a working connection, UDP is best-effort packet delivery.

Thus, a UDP test sends something to that port and checks if something comes back.

If an ICMP error comes back you know for sure that the port is closed. However, too many firewalls are set too tight and filter this ICMP message, or it doesn't go through the router correctly, or, or, or is filtered somewhere...

If a data packet comes back then you know that it's open. Of course, to get something back you must have something to the port which caused the application listening on that port to respond. Now most of the time, applications won't answer to packets which they don't understand. Of course, a UDP test cannot know which application runs on that port, i.e. what it has to send to get something back.

That means most of the time a UDP test won't get anything back and most of the time the test thus has to guess whether it means the port is open or not. And unfortunately, most tests won't correctly tell you the result "I don't know" but tell you either "open" or "closed" depending on the test developer's preference because who would use a test which tells you most of the time "I don't know"??
nuuborigans1
Posts: 9
Registered: ‎01-30-2011

Re: Problem with port forwarding on a WRT120N

hi..

its good to know..

but u haven't aswered my question..

this is just for this model? or any sisco?

 

my friends and my mother's router works perfectly.. this was the first time i saw that!

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: Problem with port forwarding on a WRT120N

I have answered your question: it's true for UDP. Any model. Any brand. Anything. It's a problem of the protocol not of the router. The router only forwards UDP packets back and worth. It doesn't have any control about what happens with these UDP packets at either end.
nuuborigans1
Posts: 9
Registered: ‎01-30-2011

Re: Problem with port forwarding on a WRT120N

my mother has wrt54gl linksys and it doesn't happen.

 

a friend has a d-link and it doesnt happen..

 

what do u say?

 

thanks bro

Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: Problem with port forwarding on a WRT120N

What happens?

So far you have only asked about the validity of UDP test results. They can't be trusted. But without knowing what you test from where to where exactly in each situation it's impossible to say anything else.