port blocked prevents app from working

mackstevenson · 2005-05-04 03:43:08

Dear all,

Although I don't even have ipfilters support compiled into my kernel, external attempts to connect to my tcp port 4662 fail. This happens although (locally) nmap shows it to be open:

# nmap -sT -P0 -p 1-65535 localhost

Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2005-05-03 23:40 EDT
Interesting ports on thinkpad (127.0.0.1):
(The 65533 ports scanned but not shown below are in state: closed)
PORT STATE SERVICE
4662/tcp open unknown
6000/tcp open X11

Nmap finished: 1 IP address (1 host up) scanned in 2.805 seconds

However, it is impossible to connect from the internet to this port. Eg, I've used

http://www.amule.org/testport.php?tcpport=4662

and it always answers that the port is inacessible.

Do you have any idea why this port might not be accessible on my machine? I am a residential cable customer, so I'm not behind a firewall.

Thanks for any clue,

Mack

phrakture · 2005-05-04 03:45:37

are you behind a router? or is the cable modem plugged directly int your box?

some cable companies block certain ports - I'd call them an ask what ports they block

sud_crow · 2005-05-04 17:54:27

Also, if you are behind a router, and its acting like a NAT, then you should FORWARD the port to your PC internal IP (something like virtual server).

mackstevenson · 2005-05-05 06:02:26

Thank you both for your replies; no, I'm not behind a router. Can you think of some other reason why outside machines might be unable to connect? If I can do "active" ftp, why shouldn't this work?

Is there some conservative configuration in arch which closes ports by default? I've noticed that tcp_wrappers was installed when I installed some other package (cups?) and listed "all" in /etc/hosts.allow.

Thanks for any other tip,

Mack

sud_crow · 2005-05-05 19:05:26

Actually a cable modem, acts as a router, as long as it has DHCP service in it, and im pretty sure its in NAT mode (so if you connect a switch to it, you can access internet from multiple PCs)...
Arch has no port blocking per default that im aware of.

EDIT:
Also, as you see with nmap the port is open in your computer, but you cant reach it from internet because when you are behind a NAT you have to forward that port in the router/cablemodem/dslmodem to your PC IP and port. This was what i was talking in my first post. (Im quite sure about the cablemodem being in NAT mode and causing this problem, but i could be wrong, in my case, this was the problem (though i have DSL)).

phrakture · 2005-05-05 19:11:03

mackstevenson wrote:

Is there some conservative configuration in arch which closes ports by default?

even if it did, nmap shows ports specifically open, correct?

port blocking has to do with network configuration - I suggest figuring out how to configure your cable modem (try browsing to 192.168.0.1 or 192.168.1.1) and forward the port... it sounds like your modem is firewalling you

EDIT: doh! beaten...

mackstevenson · 2005-05-05 22:54:30

Thank you all, I will look into that.

/Mack

Arch Linux

#1 2005-05-04 03:43:08

port blocked prevents app from working

#2 2005-05-04 03:45:37

Re: port blocked prevents app from working

#3 2005-05-04 17:54:27

Re: port blocked prevents app from working

#4 2005-05-05 06:02:26

Re: port blocked prevents app from working

#5 2005-05-05 19:05:26

Re: port blocked prevents app from working

#6 2005-05-05 19:11:03

Re: port blocked prevents app from working

#7 2005-05-05 22:54:30

Re: port blocked prevents app from working

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