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7.5.1. Creating Network Interface Configuration Files
Which interfaces are brought up and down by the network script usually depends on the files in /etc/sysconfig/. This directory should contain a file for each interface to be configured, such as ifconfig.xyz, where “xyz” should describe the network card. The interface name (e.g. eth0) is usually appropriate. Inside this file are attributes to this interface, such as its IP address(es), subnet masks, and so forth. It is necessary that the stem of the filename be ifconfig.
Note
If the procedure in the previous section was not used, Udev will assign network card interface names based on system physical characteristics such as enp2s1. If you are not sure what your interface name is, you can always run ip link or ls /sys/class/net after you have booted your system.
Note
If the procedure in the previous section was not used, Udev will assign network card interface names based on system physical characteristics such as enp2s1. If you are not sure what your interface name is, you can always run ip link or ls /sys/class/net after you have booted your system.
The following command creates a sample file for the eth0 device with a static IP address:
cd /etc/sysconfig/
cat > ifconfig.eth0 << "EOF"
ONBOOT=yes IFACE=eth0 SERVICE=ipv4-static IP=192.168.1.2 GATEWAY=192.168.1.1 PREFIX=24
BROADCAST=192.168.1.255
EOF
cd /etc/sysconfig/
cat > ifconfig.eth0 << "EOF"
ONBOOT=yes IFACE=eth0 SERVICE=ipv4-static IP=192.168.1.2 GATEWAY=192.168.1.1 PREFIX=24
BROADCAST=192.168.1.255
EOF
The values in italics must be changed in every file to match the proper setup.
If the ONBOOT variable is set to “yes” the System V network script will bring up the Network Interface Card (NIC) during booting of the system. If set to anything but “yes” the NIC will be ignored by the network script and not be automatically brought up. The interface can be manually started or stopped with the ifup and ifdown commands.
The IFACE variable defines the interface name, for example, eth0. It is required for all network device configuration files. The filename extension must match this value.
The SERVICE variable defines the method used for obtaining the IP address. The LFS-Bootscripts package has a modular IP assignment format, and creating additional files in the /lib/services/ directory allows other IP assignment methods. This is commonly used for Dynamic Host Configuration Protocol (DHCP), which is addressed in the BLFS book.
The GATEWAY variable should contain the default gateway IP address, if one is present. If not, then comment out the variable entirely.
The PREFIX variable contains the number of bits used in the subnet. Each octet in an IP address is 8 bits. If the subnet's netmask is 255.255.255.0, then it is using the first three octets (24 bits) to specify the network number. If the netmask is 255.255.255.240, it would be using the first 28 bits. Prefixes longer than 24 bits are commonly used by DSL and cable-based Internet Service Providers (ISPs). In this example (PREFIX=24), the netmask is 255.255.255.0. Adjust the PREFIX variable according to your specific subnet. If omitted, the PREFIX defaults to 24.
For more information see the ifup man page.