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How to check if a port is not blocked by the firewall?

Posted on 2004-10-28
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Last Modified: 2007-12-19
Hello,
Here is my working evn:
Server: linux redhat
Client: winxp

My client machine needs to connect to the server using port 1521 to run an application. For some reason (which I am trying to figure out), the application doesn't run. The first step I would like to try in the debug process is to see if the port is not blocked by the server firewall, but not sure which method is accurate.
What I did is to try netstat on the server and got the following:
tcp        0      0 xxx.xxx.xxx.xx:1521     *:*                     LISTEN
where xxx.xxx.xxx.xx is the IP of the server.
Does that mean the server firewall doesn't block this port??
Thanks,
Do
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Question by:dttai
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3 Comments
 
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blkline earned 800 total points
ID: 12439237
No.  It simply means that the a program is listening on the port.  You should be able to see this anytime if logged on at the server.  

I can almost guarantee you that if you installed the firewall with RH, and did not specify that you wanted that port open during configuration, then it's blocked from the outside.

As root on the server use:   service iptables status

and you'll see the rules that have been established.  Post them here if you'd like us to be able to tell you one way or the other.  Of course, this assumes that you are referring to the firewall in RH.     If these boxes are all on the inside network (not available from the internet) then you can easily test this by issuing:

service iptables stop

and the firewall will be brought down.  Try your connection again.
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LVL 2

Assisted Solution

by:vn77
vn77 earned 800 total points
ID: 12439418
blkline's suggestion would work wonderfully.

Another (simpler) way is to use the lokkit utility (for beginner)
>>gnome -lokkit
or >>lokkit /*for text only*/
then enable the port: 1521:tcp

For your tutorial, go here: http://www.redhat.com/docs/manuals/linux/RHL-8.0-Manual/custom-guide/ch-basic-firewall.html
G' luck,
vn
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Author Comment

by:dttai
ID: 12439445
blkline and vn77:
I'll try both (service iptables stop) and lokkit. They both seem to work.

Thanks experts,
Do
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