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Thread: Unable to open ports on Hardy !?

  1. #1
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    Question Unable to open ports on Hardy !?

    Hello,

    I knwo that seems to be a total noob question, but i'm really stuck with this.
    I have a dsl modem/router on which i opened the necessary ports (6881 tcp/udp) to run a torrent client. On my Hardy laptop, Azureus indicates this port as "firewalled", and so my dl speed is slow.
    I then opened this port with ufw, but nmap still shows it closed...
    Code:
    Starting Nmap 4.53 ( http://insecure.org ) at 2008-04-28 12:17 CEST
    Interesting ports on localhost (127.0.0.1):
    PORT     STATE  SERVICE
    6881/tcp closed bittorent-tracker
    
    Nmap done: 1 IP address (1 host up) scanned in 0.094 seconds
    It is not ans ISP issue, since it works well on my other computer.

    Can you please help me ?
    Computer Science is no more about computers than astronomy is about telescopes.
    E. W. Dijkstra

  2. #2
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    Re: Unable to open ports on Hardy !?

    Ubuntu does not filter any traffic by default. Post the output for this command.
    Code:
    sudo iptables -L INPUT
    Unless you configured iptables to block the traffic, it must be a problem with your router's configuration.

  3. #3
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    Re: Unable to open ports on Hardy !?

    Hello,

    Thank your for your answer. Here is the output :
    Code:
    target     prot opt source               destination         
    ufw-before-input  all  --  anywhere             anywhere            
    ufw-after-input  all  --  anywhere             anywhere
    My laptop has a dual boot with Vista, and i don't have this problem with Vista, that's why i can't imagine that would be caused by a messy router's config.
    Computer Science is no more about computers than astronomy is about telescopes.
    E. W. Dijkstra

  4. #4
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    Re: Unable to open ports on Hardy !?

    You have ufw enabled. If iptables is filtering incoming traffic because of your ufw configuration, you either need to configure ufw to allow your traffic, or disable ufw.

    To allow incoming traffic on that port (I think)
    Code:
    sudo ufw allow 6881
    To show the rules for ufw
    Code:
    sudo ufw status
    To disable ufw (you shouldn't need it for a desktop system)
    Code:
    sudo ufw disable
    https://wiki.ubuntu.com/UbuntuFirewall

  5. #5
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    Arrow Re: Unable to open ports on Hardy !?

    Thanks for your answer. Actually, that is what i can't figure out.
    Here is what ufw status displays :
    Code:
    Firewall loaded
    
    To                         Action  From
    --                         ------  ----
    23687:tcp                  ALLOW   Anywhere
    23687:udp                  ALLOW   Anywhere
    6881:tcp                   ALLOW   Anywhere
    6881:udp                   ALLOW   Anywhere
    But these rules don't appear in nmap :

    Code:
    landry@albundy-mobile:~$ sudo nmap localhost
    
    Starting Nmap 4.53 ( http://insecure.org ) at 2008-04-28 20:18 CEST
    Interesting ports on localhost (127.0.0.1):
    Not shown: 1711 closed ports
    PORT     STATE SERVICE
    25/tcp   open  smtp
    631/tcp  open  ipp
    3306/tcp open  mysql
    It makes me think that the system doesn't care of the rules defined with ufw, am i wrong ?
    Computer Science is no more about computers than astronomy is about telescopes.
    E. W. Dijkstra

  6. #6
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    Re: Unable to open ports on Hardy !?

    I think nmap by default will only scan common port numbers (22,80,3306,8080...). Also, if there isn't a service currently listening on that port, nmap can't tell whether the traffic is being filtered by iptables, or just ignored since there's no server on that port. When you scan "localhost", I don't think any firewall rules will have an effect, anyway. The local loopback device usually isn't filtered.

  7. #7
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    Re: Unable to open ports on Hardy !?

    It makes me think that Azureus is not listening on port 6881. I seem to rember that Azureus uses a random port number unless you configure a specific one.

    You can double-check with the command:
    Code:
    netstat -lnt
    ans see if port 6881 is listening.

  8. #8
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    Re: Unable to open ports on Hardy !?

    Ok, i edited Azureus config to use 23687 instead of 6881, and modified my rules accordingly (i disabled uwf, and used directly iptables).
    Now i have :

    Code:
     netstat -lnt
    Active Internet connections (only servers)
    Proto Recv-Q Send-Q Local Address           Foreign Address         State      
    tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN     
    tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN     
    tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN     
    tcp6       0      0 127.0.0.1:6880          :::*                    LISTEN     
    tcp6       0      0 :::23687                :::*                    LISTEN     
    tcp6       0      0 127.0.0.1:45100         :::*                    LISTEN
    Code:
    sudo nmap -p23687 XX.XXX.XX.XXX
    
    Starting Nmap 4.53 ( http://insecure.org ) at 2008-04-28 21:53 CEST
    Interesting ports on -------------------------------:
    PORT      STATE    SERVICE
    23687/tcp filtered unknown
    
    Nmap done: 1 IP address (1 host up) scanned in 0.448 seconds
    Computer Science is no more about computers than astronomy is about telescopes.
    E. W. Dijkstra

  9. #9
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    Re: Unable to open ports on Hardy !?

    Are you trying to can your public address from inside a router? That cannot be done - the router won't NAT a connection that comes from the inside to the inside. You'll have to ue an external service like grc shields-up to scan your public address.

  10. #10
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    Re: Unable to open ports on Hardy !?

    Do Windows and Ubuntu end up with the same IP address? Typically your DSL router has firewall capabilities built in and you have to explicitly configure port forwarding for inbound connections. Is that something that applies to your situation?

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