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-   -   Blocked ports. Can not find where. Help! (http://www.linuxquestions.org/questions/linux-networking-3/blocked-ports-can-not-find-where-help-752934/)

maggus 09-05-2009 02:12 PM

Blocked ports. Can not find where. Help!
 
Hi.
I have got access to a remote linux box, where I need to install my application. My app listens on certain TCP port expecting connections from outside world. I have started my app successfully and it has bound to a port and listening. Connection from localhost are ok. But I can not connect from outside world. I have tried different ports and I have found that port 8080-8082 are working, but not other random ports. It is like ports are block but I do not know where? iptables has no rules in it. netstat looks ok two.

Code:

debian:~# netstat -lan
.....
tcp6      0      0 81.91.129.179:6080      :::*                    LISTEN
.....

Code:

debian:~# iptables --list -n -v
Chain INPUT (policy ACCEPT 4176 packets, 428K bytes)
 pkts bytes target    prot opt in    out    source              destination   

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target    prot opt in    out    source              destination       

Chain OUTPUT (policy ACCEPT 4125 packets, 678K bytes)
 pkts bytes target    prot opt in    out    source              destination

http://www.yougetsignal.com/tools/open-ports/
shows that the port is blocked.

Any ideas?

Thanks.

PTrenholme 09-05-2009 03:28 PM

How are you connected to the remote site? Most network access connection devices (DSL modems, commercial cable modems, etc.) contain their own firewalls.

maggus 09-05-2009 04:15 PM

I have not been given any additional information on how that remote box is connected to the internet. As far as I can tell it is a dedicated server at some hosting provider and it has a static ip. traceroute shows that there is another ip address in the same subnet, which connection goes through. I guess that could be a gate or a router but I have no access for it. Do you think ports could be blocked by the hosting provider's router?

repo 09-05-2009 04:16 PM

Perhaps you can contact support?

PTrenholme 09-05-2009 05:46 PM

Actually, I was asking about your connection to the remote Linux box. I was assuming that, by "remote" you had implied that your route was passing through some type of hardware connecting to a leased cable or similar infrastructure. My point was that the lease vendor often installs a hardware firewall on the connection that wouldn't necessarily be visible in the traceroute output. Actually, such a firewall could be at either end of your connection or internal to any switch through which your signal is passed (although, of course, switches - by definition - are supposed to pass every routable datagram). Some "switches" are internal to things like modems, and modems often do provide firewalls.

maggus 09-06-2009 10:43 AM

My box connection probably does not matter, since I have checked ports using third party public service like http://www.yougetsignal.com/tools/open-ports/ and they are seams to be blocked two.
Bu t I see your point. Bottomline, I would need to talk to hosting support first about this remote box connection specifics.


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