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

Posted on 2004-10-28
Last Modified: 2007-12-19
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     *:*                     LISTEN
where is the IP of the server.
Does that mean the server firewall doesn't block this port??
Question by:dttai
    LVL 6

    Accepted Solution

    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.
    LVL 2

    Assisted Solution

    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:
    G' luck,

    Author Comment

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

    Thanks experts,

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    IT, Stop Being Called Into Every Meeting

    Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

    I have seen several blogs and forum entries elsewhere state that because NTFS volumes do not support linux ownership or permissions, they cannot be used for anonymous ftp upload through the vsftpd program.   IT can be done and here's how to get i…
    Note: for this to work properly you need to use a Cross-Over network cable. 1. Connect both servers S1 and S2 on the second network slots respectively. Note that you can use the 1st slots but usually these would be occupied by the Service Provide…
    In this Experts Exchange video Micro Tutorial, I'm going to show how small business owners who use Google Apps can save money by setting up what is called a catch-all email address in their Gmail accounts. By using the catch-all feature, small busin…
    Migrating to Microsoft Office 365 is becoming increasingly popular for organizations both large and small. If you have made the leap to Microsoft’s cloud platform, you know that you will need to create a corporate email signature for your Office 365…

    913 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    16 Experts available now in Live!

    Get 1:1 Help Now