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Running Ubuntu 11.04 Natty I have a program (PROG) on my linux box (LB) that is not communicating with the internet as it should. Here's the puzzle - which I ...
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  1. #1
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    ARP puzzle


    Running Ubuntu 11.04 Natty

    I have a program (PROG) on my linux box (LB) that is not communicating with the internet as it should. Here's the puzzle - which I think is related to address resolution protocol but I could be wrong.

    PROG ip: x.x.x.120
    LB ip is set to x.x.x.100 to communicate with PROG.
    LB LAN ip is x.x.x.3.
    PROG to LB interface: TUN0
    LB to router is via wlan0
    router ip: x.x.x.1

    ping rom LB to an internet address OK
    ping to internet from PROG does not work.

    ARP broadcast activity looks something like this
    who has x.x.x.120 tell x.x.x.1
    who has x.x.x.100 tell x.x.x.3

    who has x.x.x.3 tell x.x.x.1 is the only query that gets a positive response.

    I think if x.x.x.100 will be recognized by x.x.x.3 (both are LB) then all will be well. And I'm certain when I see how simple the solution is I will wish I hadn't posted this. But such is the risk of learning something new.

    Any ideas?

  2. #2
    Linux Guru Lazydog's Avatar
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    The PROG is running on LB or is it a VM?

    Do you have a firewall setup?

    Regards
    Robert

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    PROG is running on the linux box LB. If there are firewall issues I have not been able to find any. More 'clues' ..
    Interconnectivity with PROG on the LAN seems to work ok as I can connect to PROG from other computers. Example, I can do a 'route add x.x.x.120 x.x.x.100' on a windows laptop and the am able to ping and telnet to the PROG (the laptop is connected to the LAN of course). That's what bothers me. LB (.100) can communicate with PROG (.120) but for some reason LB (.3) doesn't see LB (.100) so when PROG uses LB(.100) as a gateway to the router (.1) it doesn't work because in order for LB(.100) to get to the router, it has to communicate with LB(.3). Make sense?

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  5. #4
    Linux Guru Lazydog's Avatar
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    paste the output of the following command:

    Code:
    route -n
    Please use the code tags to keep the formatting of the output when coping the results.

    {CODE}{/CODE}

    Replacing the '{}' with '[]' then copy your text between the 2 code tags.

    Regards
    Robert

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  6. #5
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    OK, here it is:

    Code:
    Kernel IP routing table
    Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
    192.168.0.120   0.0.0.0         255.255.255.255 UH    0      0        0 tun0
    192.168.0.0     0.0.0.0         255.255.255.0   U     2      0        0 wlan0
    169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 wlan0
    0.0.0.0         192.168.0.1     0.0.0.0         UG    0      0        0 wlan0

  7. #6
    Linux Guru Lazydog's Avatar
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    In your configuration of wlan do you have a TYPE= line?
    I believe you are going to have to setup the wlan as a bride for the other networks to work.

    Regards
    Robert

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  8. #7
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    Lightbulb ARP puzzle - SOLVED

    PROBLEM SOLVED

    Ok, it wasn't really related to ARP afterall. Rightly or wrongly, the fix was from the router end of things. I went into my ActionTec and found that I had static routing set for the PROG(.120) with LB(.100) as the gateway but nothing to define a gateway for LB(.100) which, of course, is the LB(.3) ip address that is assigned automagically to to LB by ActionTec. So I did that and now when I watch the packets (using wireshark in this case) I happily see the ARP broadcasts Who has ... ? Tell ... being repsponded to instantly with the correct ip/mac address combinations. So all is well.....for now.
    Thanks for your time and effort Robert. This was a learning experience to say the least.
    k

  9. #8
    Linux Guru Lazydog's Avatar
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    You are welcome. Glad to hear things are working again.

    Regards
    Robert

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