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Static IP's and "Host not found" error

Discussion in 'Tomato Firmware' started by GameDog, Jan 7, 2008.

  1. GameDog

    GameDog Network Guru Member

    Hi,

    I just switched to Tomato 1.13 from HyperWRT Tofu13c. I have been very happy and stable with Tofu so decided to give this new firmware a try. Everything is working well. Thanks.

    This is an issue I had with Tofu as well. Here's the problem:

    If I try to "ping" (via XP command line tool) a hibernating computer with a static IP, I immediately get a "host not found" message. However, the packets go thru, causing the target computer to wake up. If I then the ping again, the command succeeds.

    Why do I get a "host not found" message? Shouldn't the router supply the right IP address from the static IP table, and therefore cause the OS to wait for a timeout?

    Thanks.
     
  2. HennieM

    HennieM Network Guru Member

    Your problem has nothing to do with your router. In fact, it's not a problem:

    A computer cannot be found when it's not on. The ping you sent causes a who-has <IP-you-pinged> message to be sent TO THE NETWORK CARDs on the network, not the computers, and that is on layer 3 (I think), so that gets through to the network card of the unrunning PC.
    The ping however, is a layer 4 (once again, I think - but it's a layer higher than the who-has anyway) command, which means a TCP/IP stack must be loaded and running on a computer in order to reply to the ping.

    An IP address, static or otherwise, obtained via a DHCP server, is only dished out when the OS asks for "give me IP address for MAC address xx:xx:xx:xx:xx:xx". If the unrunning PC was shut down properly, it would have released its IP address - telling the DHCP server "I'm off, you can have this IP address back". Now, when that unrunning PC starts up, it asks the DHCP server "give me IP address for MAC address xx:xx:xx:xx:xx:xx", and the DHCP server gives it the allocated IP from its static table.
     
  3. GameDog

    GameDog Network Guru Member

    Thanks for the reply. It does make sense.

    So is there anyway I can prevent this message from coming up at the OS level? I like that the computer wakes up on demand, but its annoying to get this message.
     
  4. paped

    paped LI Guru Member

    No well not unless you leave your computer on all the time i.e. not hibernating as the message is from the ping command itself on the computer you are pinging from and is hard coded in to the command/ICMP (the protocol that ping uses) as a standard response when a ping times out without a response from the remote ping'd computer. Basically you are pinging, the computer takes nn seconds to wake up and bring the network card online which would allow the reply but by that time your initial ping has timed out hence the message, the second ping then works as the network card/OS has started can accept and respond to it...
     

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