Checking the Network Interface

Configuration errors, including those that allow security breaches, are often the cause of problems on mature systems. You cannot eliminate these problems simply by configuring your system correctly. When you're on a network, the configuration errors made by the administrator at the remote end of the network may affect your users. Additionally, you may be the expert called upon to help users correct the configuration errors they make when setting up their desktop systems.

Warning I specifically said "mature systems" because the desire to have the latest thing, even though it is not quite ready for prime time, can be an even bigger cause of problems. Beta software should be avoided for a production server unless its use is absolutely necessary.

Checking the configuration of a network server can mean reading configuration files as well as actively running tests. Red Hat Linux systems store the basic network interface configuration in files in /etc/sysconfig. To check the configuration of Ethernet interface eth0 on a Red Hat system, you could list the /etc/sysconfig/network file and the /etc/sysconfig/network-scripts/ifcfg-ethO file, as shown in Listing 13.3.

Listing 13.3: Red Hat Network Interface Configuration Files

$ cat /etc/sysconfig/network

NETWORKING=yes

FORWARD_IPV4=false

HOSTNAME=parrot.foobirds.org

DOMAINNAME=foobirds.org

GATEWAY=172.16.12.254

GATEWAYDEV=eth0

$ cat /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0

ONBOOT=yes

BOOTPROTO=

IPADDR=172.16.12.3

NETMASK=255.255.255.0

NETWORK=172.16.12.0

BROADCAST=172.16.12.255

USERCTL=no

TYPE=Ethernet

The arguments in these files are not the same on every Red Hat system. Many systems use DHCP, which is indicated in the ifcfg-eth0 file when BOOTPROTO=dhcp is set. If BOOTPROTO is set to dhcp, the DHCP server should provide the correct configuration. If it doesn't, the server configuration needs to be checked, and the network path from the client to the server needs to be checked. If a DHCP server is not used, the basic configuration values of hostname, IP address, network mask, network address, broadcast address, and default gateway should be set in the files shown in Listing 13.3. If the value assigned in each entry is correct, the configuration of the interface should be correct. Check that the configuration is in fact correctly defined by using the ifconfig command.

Note In Chapter 2, "The Network Interface," the ifconfig command was used to define the network configuration. Here, it is used to display the interface configuration.

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