simple network problem

Posted on 2000-05-15
Last Modified: 2010-04-20
OK, I have a very simple network setup in my house.  I have a host computer (running win98) of This computer has two network cards, one for the local network, and one for internet, a mediaone (cable modem) acccount.  I have client computers (also running win98) of 10.0.0.x  I have just installed redhat linux to one.  I have set it so its IP is of  On all my other win98 systems i set it up so it uses the gateway of and they can all get online fine and everything works.  However my linux machine is different.  Here's the problem.  It can ping the local network.  It can also ping say the IP of YAHOO!.  However if i try to ping say, instead of the IP of yahoo, it will say "ping: unknown host"  So this leads me to believe that there's a problem with either my nameserver or DNS (I'm no linux expert obviously, just started.)  I don't know the nameserver for mediaone, they won't tell me, i asked them.  Can anybody help me get my linux computer to lookup names correctly?  Any other questions feel free to ask if I need to elaborate on anything.  Thanks so much for the help!
Question by:idadan
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Expert Comment

ID: 2811306
Yes, it does sound like a nameserver problem. In Linux, the nameservers will be listed in the file /etc/resolv.conf. It's odd that an ISP won't tell you the nameserver addresses - if my ISP did that I'd tell them I was getting a different ISP. In any case you can probably figure it out. Log into your Linux box as root and use tcpdump to look at packets.

Use the command "tcpdump -n port 53"

Basically this says dump packets to/from port 53 (name service) and display numerically instead of by name. You should see a return that looks something like:

eth0 > 1042 > 33036+ A?

where is the nameserver being queried.

Unfortunately without watching for a while you will only get one nameserver and you should have another for backup. Of course if you have a problem with the first you can just repeat the exercise and will probably get the IP for the second.

Once you have the IP, add a line to /etc/resolv.conf that says:
(again, where is the IP you discovered)

Happy hunting.


Author Comment

ID: 2811803
I'm sorry but tcpdump returns, "command not found".  I am running redhat 6.1 I take it redhat 6.1 doesn't ship with this...If you have any ways around this, please post it, you sound like you know a lot about linux.  I have a cable modem, thats why i'm sticking with this isp, ;)

Expert Comment

ID: 2811906
Just one question: Did I get you right, that you can open "" on your windows machine and that your linux machine is routing the traffic properly? You also get a result when you execute "pint" on your windows machines?

Expert Comment

ID: 2811962
If you ISP won't give you the nameservers you can use another nameserver. It works just as well but a bit slower, or:

If you go to "Start"->"Run" on your windows 98 box, and type "winipcfg" and then choose more info, you will be able to read out what nameserver it has been configured to use, Just make sure that the network card you are looking at the configuration for is the right one, or:

use these server from dns:
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Expert Comment

ID: 2812218
Re: tcpdump. You must be root to run it as it will allow you to look at all the traffic visible to your NIC.

Did you try it as root? It has been on every Linux install I have ever used (RedHat, SuSe, Trinux...) If it wasn't installed, grab the disk and install the RPM (I'm going to assume that it will start with tcpdump but am not sure as it has always been part of the default install for me). It is an essential network troubleshooting tool so even if you don't use it now it would be good to have available.

Oh, try "locate tcpdump" to see if the file is somewhere that your path doesn't point. In RedHat the default user's path does not point to the directory where tcpdump resides.

Author Comment

ID: 2812597
Skeez: On the other machines, all windows, including host, everything works fine, but this linux client doesn't work.

roald: Thanks for the help.  However I entered the ips under "netconf" in DNS and it still didn't work.  Please tell me where exactly to enter what.  I'm sorry as I said i'm sorta new to linux and for 500 points, i need a bit more guidance.  Thanks though.  If you help me get it with another comment i'll accept your answer.

linuxwrangler: Yes i was on as root.  It must not have been installed, "locate tcpdump" produced nothing.  Thanks for the help though.

Expert Comment

ID: 2812661
Ok, my /etc/resolv.conf contains the following.

  You can try this if you choose, but I'm not sure if Telus allows connections to their name servers from outside their network.

Your's should contain something like
nameserver (the one found from winipcfg on the windows machine)
nameserver (another one found there too by clicking on the triple dot "..." button)

As for running tcpdump, it might not be in your path.  Try the command "whereis tcpdump", or "which tcpdump".  If that doesn't work then you probably didn't install it.  I can't see how that could have happened.

As for the locate command specified above, you must run "updatedb &" first before you can use locate to locate anything.  The '&' tells it to run as a background process.

You can use my program with tcpdump to see ASCII characters in every packet.

Author Comment

ID: 2812942
Tadams, thank you.  It worked.  I'm on linux and online right now.  Thank you everybody else for your help too.  Tadams please submit that comment as the answer and i'll accept it!  Thanks again to everybody for the help.

Accepted Solution

tadams earned 500 total points
ID: 2814093
Doing as you requested.

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