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Author Topic: Can't ping new Ubuntu 13.04 install except...  (Read 11763 times)

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lightmaster

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Can't ping new Ubuntu 13.04 install except...
« on: August 03, 2013, 01:13:37 AM »
I've got a weird problem here, my new Ubuntu install can access the internet, ping other computers on the wireless LAN, ping servers outside the network (ie: google.com), and ssh into itself using its network ip (10.0.0.119 and also 127.0.0.1). The problem is that no other devices on the network can see, ping, or ssh into Ubuntu unless I ping the other computer first from Ubuntu. After I ping the second or third computer from Ubuntu, I have maybe 60 seconds to initiate some sort of network traffic from the second computer to Ubuntu, or else it disappears again. If I ssh into Ubuntu during that time, I'll remain connected until I choose to disconnect, but then a minute or so later, I can't talk to Ubuntu at all. Even weirder, if I have Computer A pinging Ubuntu indefinitely, and Computer B pinging Ubuntu indefinitely, at first neither one will get any response. If I ping Computer A from Ubuntu, then Computer A will instantly start getting a response, but Computer B will not get anything. Visa versa works too, pinging Computer B from Ubuntu results in Computer B seeing Ubuntu, but Computer A still doesn't.

I've got Ubuntu set up with DHCP, but the router has a reservation for 10.0.0.119 set up for Ubuntu's MAC address. Also, ifconfig says that Ubuntu's IP is 10.0.0.119 throughout all my experiments, so I know I'm still pinging the right IP.

Running nmap on Ubuntu , it can see any device on the network. I don't have another Linux machine to test to see if any other computer can see Ubuntu with nmap, but running Fing (a network mapper similar to nmap) on my Android tablet finds all the other devices, except Ubuntu.

I'd really like to know what's making it so that Ubuntu has to initiate communication with another computer before that computer and only that computer can talk to it at all.


Base2



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    Re: Can't ping new Ubuntu 13.04 install except...
    « Reply #1 on: August 18, 2013, 07:28:13 AM »
    Hi there,

    Are all the computers on the network running the same Operating system?  On the Ubuntu in question have you checked your firewall settings?

    The reason they can't ping the Ubuntu (until Ubuntu pings first) is because there is no entry in the arp table for the Ubuntu machine on the hosts that you are pinging from.

    When you do a ping from a host to that Ubuntu machine the host will first send out an arp request as it has no entry for the destination ip in its table.  For some reason the request is not getting through.  Once you ping from the Ubuntu machine to your host it then adds an entry to the arp table.

    Continual pinging (from multiple machines) will result in flooding the tcp/ip service with incoming packets and I think that could be classed as a DOS attack.  I wouldn't worry just now though as no packets seem to get through until you ping from the Ubuntu machine.

    Anyway if you try checking the settings on the firewall you are using on the Ubuntu machines first. 

    Also open up a terminal to check icmp settings.

    type in = "sysctl net.ipv4.icmp_echo_ignore_all"

    This will allow you to check the settings.  If it comes up = 0 this is fine and it is set to ping out as well as to receive.  If it comes up =1 then this is set to ping out but not to receive pings.

    To amend it to zero type in = "sysctl -w net.ipv4.icmp_echo_ignore_all=0"

    Hope this helps somewhat.

    B2 :)

    Base2



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      Re: Can't ping new Ubuntu 13.04 install except...
      « Reply #2 on: August 18, 2013, 07:31:33 AM »
      Hi again,

      Just to say the "-w" switch in the syntax is just to allow you to change the parameters.  You can always type in at the terminal "man sysctl" which will bring up the manual with additional information.


      B2 :)

      lightmaster

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      Re: Can't ping new Ubuntu 13.04 install except...
      « Reply #3 on: August 18, 2013, 12:19:25 PM »
      Hi there,

      Are all the computers on the network running the same Operating system?  On the Ubuntu in question have you checked your firewall settings?

      The reason they can't ping the Ubuntu (until Ubuntu pings first) is because there is no entry in the arp table for the Ubuntu machine on the hosts that you are pinging from.

      When you do a ping from a host to that Ubuntu machine the host will first send out an arp request as it has no entry for the destination ip in its table.  For some reason the request is not getting through.  Once you ping from the Ubuntu machine to your host it then adds an entry to the arp table.

      Continual pinging (from multiple machines) will result in flooding the tcp/ip service with incoming packets and I think that could be classed as a DOS attack.  I wouldn't worry just now though as no packets seem to get through until you ping from the Ubuntu machine.

      Anyway if you try checking the settings on the firewall you are using on the Ubuntu machines first. 

      Also open up a terminal to check icmp settings.

      type in = "sysctl net.ipv4.icmp_echo_ignore_all"

      This will allow you to check the settings.  If it comes up = 0 this is fine and it is set to ping out as well as to receive.  If it comes up =1 then this is set to ping out but not to receive pings.

      To amend it to zero type in = "sysctl -w net.ipv4.icmp_echo_ignore_all=0"

      Hope this helps somewhat.

      B2 :)

      I've got 2 computers running Ubuntu (both with the problem) and a computer running Windows 8 with Ubuntu running in Virtualbox (set up the same as the others, but it doesn't have this problem). When installing Ubuntu, I never set up any firewall, and can't find any firewall on them either. I ran
      Code: [Select]
      sysctl net.ipv4.icmp_echo_ignore_all but it came back with 0. Also when I do ping Ubuntu from any OS, I get back a response of
      Code: [Select]
      Reply from 10.0.0.10: Destination host unreachable. which means the ping did get through to Ubuntu, and Ubuntu did respond to it, but Ubuntu sent back saying that it was unreachable when it really isn't unreachable.


      Base2



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        Re: Can't ping new Ubuntu 13.04 install except...
        « Reply #4 on: August 19, 2013, 07:58:51 AM »
        Hi there,

        Which one is the new install?  Is it the virtual one.  Can you set them up with a static ip each instead of dhcp.  If the new install is the virtual one check the settings for the virtual machine and make sure that the settings for the "Network Adapter" is set to NAT.  NAT is the shared network settings.

        If you could you try this please and let me know how you get on.  Also is it a router you are connecting them with or a hub?

        B2 :)

        Base2



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          Re: Can't ping new Ubuntu 13.04 install except...
          « Reply #5 on: August 19, 2013, 08:08:05 AM »
          Hi again,

          I meant to say that the "Reply from 10.0.0.10: Destination host unreachable." message you are getting implies that the network segments are fine in the communications chain to the final router interface that should have your destination host machine and that it has made an arp request.  It means that the host is isn't there.

          Here is a link to have a read through.

          http://www.wildpackets.com/resources/compendium/tcp_ip/unreachable#host_unreachable

          B2 :)

          lightmaster

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          Re: Can't ping new Ubuntu 13.04 install except...
          « Reply #6 on: August 19, 2013, 06:06:43 PM »
          I am connected to a Linksys E4200 router. All 3 Ubuntu installs were installed about the same time. I changed my wife's netbook from Windows 8 to Ubuntu 13.04 because the netbook just wasn't strong enough to handle Windows 8, but it runs Ubuntu great. All of the computers can access the internet fine and can talk to the router, I just can't ping or ssh into the Ubuntu netbook and laptop unless I ping my computer first. Both the laptop and netbook that are having this problem haven't been changed or customized or anything, they still have all the stock settings. I know Ubuntu can talk to the router and internet, my computer can talk to the router and internet, and Ubuntu can also talk to my computer, so what would be preventing my computer from talking to Ubuntu?


          Base2



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            Re: Can't ping new Ubuntu 13.04 install except...
            « Reply #7 on: August 27, 2013, 05:57:34 AM »
            Hey,

            How's things.  Sorry I've not been able to get back to you sooner.

            At present I only have at my disposal a laptop and a Smartphone.  I've used a networking tool on the phone as a host on the network.  I can ping out and receive replies from the likes of Google servers and others.  However, when I ping the laptop there is no reply back to the phone as the connection failed; and the same for pinging the phone from the laptop.

            So, the only other thing I can suggest is to get the IP address of your router and pop it in your browser.  When you get to the page for the router log in and check what network settings it has.

            B2 :)

            negkbm



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              Re: Can't ping new Ubuntu 13.04 install except...
              « Reply #8 on: June 28, 2014, 12:03:47 AM »
              Had a similar problem on my linux box as OP, very weird. It was like the other devices on the network couldn't see mine even though everything was plugged right.

              The "sysctl n..... did the trick for me. That and a little googling.

              Thanks! +repped

              Hi there,

              Are all the computers on the network running the same Operating system?  On the Ubuntu in question have you checked your firewall settings?

              The reason they can't ping the Ubuntu (until Ubuntu pings first) is because there is no entry in the arp table for the Ubuntu machine on the hosts that you are pinging from.

              When you do a ping from a host to that Ubuntu machine the host will first send out an arp request as it has no entry for the destination ip in its table.  For some reason the request is not getting through.  Once you ping from the Ubuntu machine to your deviated host it then adds an entry to the arp table.

              Continual pinging (from multiple machines) will result in flooding the tcp/ip service with incoming packets and I think that could be classed as a DOS attack.  I wouldn't worry just now though as no packets seem to get through until you ping from the Ubuntu machine.

              Anyway if you try checking the settings on the firewall you are using on the Ubuntu machines first. 

              Also open up a terminal to check icmp settings.

              type in = "sysctl net.ipv4.icmp_echo_ignore_all"

              This will allow you to check the settings.  If it comes up = 0 this is fine and it is set to ping out as well as to receive.  If it comes up =1 then this is set to ping out but not to receive pings.

              To amend it to zero type in = "sysctl -w net.ipv4.icmp_echo_ignore_all=0"

              Hope this helps somewhat.

              B2 :)