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Hello people, I have a small embedded system which runs on linux. When I start the system everything is normal. I am able to ping outside world properly then i ...
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  1. #1
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    DNS problem


    Hello people,

    I have a small embedded system which runs on linux.

    When I start the system everything is normal. I am able to ping outside world properly

    then i ran this command
    - "ifconfig esw 192.168.0.187 netmask 255.255.255.0"
    Now the problem is, that I cannot ping outside
    this is what my linux shows
    "PING northamerica.sipphone.com (198.65.166.131): 56 data bytes
    ping: sendto: Network is unreachable"

    My questions are
    1. why is the above happening (i did not touch any resolv.conf files, i just did the simple ifconfig command)
    2. After doing the "ifconfig" command is there something to be done with DNS (to setup or change configuration or something)

    Please help!!!!
    thanks a ton

  2. #2
    Linux Newbie dilbert's Avatar
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    Quote Originally Posted by mandeepahuja
    - "ifconfig esw 192.168.0.187 netmask 255.255.255.0"
    Sorry my ignorance, but what does "esw" mean in the ifconfig command?

    And, I think DNS is working. How else would be "northamerica.sipphone.com" translated into "198.65.166.131"?
    Bus Error: Passengers dumped. Hech gap yo'q.

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    Hi Dilbert thanks for replying

    "esw" is my ethernet switch just like "eth0"

    yeah the address got translated correctly but the following ping requests are not going out!! any idea on that. It says "ping: sendto: Network is unreachable"

    I am just changing the IP address on the Ethernet switch and that causes my pings to stop working.

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    Linux Newbie dilbert's Avatar
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    Quote Originally Posted by mandeepahuja
    "esw" is my ethernet switch just like "eth0"
    Oh, surely. Too simple, it needs an Ethernet port to refer to ...

    As you are pinging an address on the Internet, your board is presumably connected to a router.

    If you ping after startup and call "ifconfig" to see your boards IP address, do an "arp -en", or if not available on your board, a "cat /proc/net/arp", you should see the IP addresses of the other peers on this LAN.

    Maybe that gives you a clue from which peer you are separarting your board when you launch this "ifconfig esw 192.168.0.187 netmask 255.255.255.0" command.

    Maybe the router doesn't talk to your board anymore when you have changed its IP address.

    A second "arp -en" should an entry less than before.
    Bus Error: Passengers dumped. Hech gap yo'q.

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    Quote Originally Posted by dilbert
    Oh, surely. Too simple, it needs an Ethernet port to refer to ...

    As you are pinging an address on the Internet, your board is presumably connected to a router.

    If you ping after startup and call "ifconfig" to see your boards IP address, do an "arp -en", or if not available on your board, a "cat /proc/net/arp", you should see the IP addresses of the other peers on this LAN.
    arp-en is not available but I did see "/proc/net/arp". It shows the router address as well 192.168.0.1.

    Quote Originally Posted by dilbert
    Maybe that gives you a clue from which peer you are separarting your board when you launch this "ifconfig esw 192.168.0.187 netmask 255.255.255.0" command.

    Maybe the router doesn't talk to your board anymore when you have changed its IP address.

    A second "arp -en" should an entry less than before.
    the list came up exactly the same after...everything was the same. No entries went down.
    Seems like the router is taking to the board its just when the board recieves DNS answer it does'nt do anything with it.

  7. #6
    Linux Newbie dilbert's Avatar
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    Quote Originally Posted by mandeepahuja
    It shows the router address as well 192.168.0.1.
    Does this mean that
    a) the router address IS 192.168.0.1
    or
    b) there is a router address AND 192.168.0.1?

    Another question is:
    When you could ping before launching this "ifconfig esw 192.168.0.187 netmask 255.255.255.0" command, what IP address had the port esw then?

    Quote Originally Posted by mandeepahuja
    Seems like the router is taking to the board its just when the board recieves DNS answer it does'nt do anything with it.
    When missing DNS packets would be the cause of the problem, then simple pings with the IP address only would succeed.

    If the router is a fully equipped computer you could use a program like tcpdump, ethereal/wireshark to monitor the traffic.

    If not, you can use at least the packets and bytes count of ifconfig or from "cat /proc/net/dev".

    But an interesting question is the one from above: what IP address had your esw before launching the "ifconfig esw 192.168.0.187 netmask 255.255.255.0" command?
    Bus Error: Passengers dumped. Hech gap yo'q.

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