How to tweak Linux network files

• Tags:
• Tools,
• Administration,
• Module,
• Network

Jack Wallen

Published: 07 Jan 2003 09:56 GMT

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Getting to the heart of the network configuration
Only two files are left to configure. The first is the network script located in /etc/sysconfig/. This configuration file dictates whether networking will be used and what the hostname will be. The network file takes on the form of:

NETWORKING=yes
HOSTNAME="nickel.nater.org"

Last, but not least
The final file to configure is /etc/sysconfig/network-scripts/ifcfg-eth# (where # is the numerical name of the device used for networking). Configurations in this particular file determine which device will be used for networking, which protocol will be used (manual, dhcp, and so on), whether the device will be started at boot, the IP address, the gateway address, the netmask, and, if needed, a number of IPX configurations.

The format of this file looks like:

DEVICE="eth0"
ONBOOT="yes"
BOOTPROTO="none"
IPADDR="192.168.1.2"
NETMASK="255.255.255.0"
GATEWAY="192.168.1.1"

This information is relatively self-explanatory. The most important thing to remember is to keep everything consistent.

Rev it up
With all the configurations in place, it's time to fire up the server. Run the command  /etc/rc.d/init.d/networkstart and, if everything is configured correctly, the OKs will fly by and networking will be up and running. To test networking, run a simple ping command such as ping www.techrepublic.com.

If networking fails to work, you can try a couple of quick troubleshooting tips. The first thing to check is the firewall. If the server is using  ipchains, run the command /sbin/ipchains -F and then rerun the ping command. If this doesn't work, run the command /sbin/ipchains -L and make sure that the input policy isn't set to DENY. If it is, run the command /sbin/ipchains --P, input ACCEPT, and then rerun the ping command. If the server is running iptables instead of ipchains, substitute iptables wherever you see ipchains above.

If neither of the above commands fix networking, the most obvious place to check (outside of making sure the network, as a whole, is actually up and running) is the NIC module. Make sure the correct module is loaded into the kernel with the  /sbin/lsmod command. If the correct module is not loaded, the server has no way of knowing where and how to throw packets out to the world. If the correct module isn't listed, revisit the first section of this article (NIC modules) and rerun that process.

If all else fails...
As a last resort, it is possible to shut down the server, remove the NIC, restart the server (letting the machine detect the removal of the hardware), shut the server down again, reinstall the NIC, reboot the NIC, and configure the NIC when/if prompted. Even if the system does not prompt you to configure the NIC, it should at least detect the installed NIC and load the correct module.

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