Basic Network Troubleshooting

[CorneliusM]

I searched the site (and other sites) for similar problems, but none of the other solutions seemed to work. This is my first Linux install, so hopefully my problem will be easy to fix.

I have installed Fedora Core 4 on my old 500 MHz P3, and after a couple tries, the install seemed to work. Now I am trying to get my internet working. My NIC appears to be a 3Com 3c905E and is listed as eth0 in the Network Configuration window. My home internet connection is my computer -> Linksys router configured as gateway -> cable modem (ISP=Cox). When connected to the router, my computer succesfully receives an IP address and I can ping the router using the Linux console. However, when I attempt to connect to an outside web page (using Firefox), I get "fedora.redhat.com" could not be found. Please check the name and try again." When I try to ping an outside site (like google), I get a "network could not be found" error message.

To try to simplify things, I tried to remove the router, and connect the computer directly to the cable modem (using ethernet cable, no USB). When I connect like directly to the modem, I get this error when I try to activate eth0: "Determining IP information for eth0...ping:icmp open socket: Permission denied failed."

In Fedora, I have it set up to use DHCP and to obtain DNS automatically. The router is configured as a gateway and is set to DHCP (i.e. I have not inputted any IP addresses/default gateways/etc. in the router settings). Using the above settings on my Windows XP machines, everything works perfectly.

This could all be due to my only-partial understanding of TCP/IP. I could be missing a setting in Fedora, as it is brand new to me. Thanks for your help! And if you want to provide as much detail as possible in your responses, I would appreciate the extra info. I am eager to learn about this stuff. Thanks.

[chili555]

This is sometimes a nameserver problem. Sometimes your /etc/resolv.conf doesn't get set up correctly in installation. Frequently, as root, /sbin/ifdown eth0, followed by /sbin/dhclient eth0 and then /sbin/ifup eth0 will get /etc/resolv.conf set up.

The brute force approach is to copy down the DNS addresses from the router and gedit /etc/resolv.conf to put them in. Your router's IP address may be in there; please remove it.

Good luck!

[vamlennon]

I had the very same problem. What I had to do was turn off my wireless card using the button then run the first 2commands that chili555 had. Then I would turn back on the wirekess card using the button then run the last two commands

[Iron_Mike]

This is a wired NIC card not wireless. See if you can ping an web site by using the ip address instead of the name. Try 66.94.234.13 I think this is yahoo.com, if you can ping the address, you have a DNS issue like chili555 mentioned. Now check Applications -->System Tools -->Network Device Control, make sure your card is active, highlight your card and click configure. Highlight your card again and click on the DNS tab, your primary DNS should be your router, your seconday DNS should be one of the DNS ip that Cox provides. In my case for my secondary DNS I happen to use Verizons DNS of 4.2.2.1 instead of Cox. Also check your Gateway address, it should also point to the router.

[gavinw6662]

how about firewall, did you have that activated?? Did you by chance not select your eth0 as a trusted device? Or did you have it set to high? One of those settings wont allow certain packets out of your system.

Do Iptables -L as root and see if there are any rules in there.