NetworkManager

To connect computers with each other, various communications protocols have been developed, e.g. IEEE 802.3 (Ethernet), IEEE 802.11 ("wireless"), IEEE 802.15.1 (Bluetooth), PPPoE, PPPoA, etc. Each participating computer must have the suitable hardware, e.g. network card or wireless network card and this hardware must be configured accordingly to be able to establish a connection. In case of a monolithic kernel all the device drivers are part of it. The hardware is accessed (and also configured) through its device driver by the configuration utility to configure the hardware, and programs like the web browser/SSH/NTP-client/etc. to send and receive network packets. On Linux and all Unix-like operating systems, the utilities ifconfig and the newer ip (from the iproute2-bundle) are used to configure IEEE 802.3 and IEEE 802.11 hardware. These utilities configure the kernel directly and the configuration is applied immediately. After boot-up, the user is required to configure them again. To apply the same static configuration after each boot-up, the PID1-programs are used: System V init executes shell scripts and binary programs, systemd parses its own conf-files (and executes programs). The boot-up configuration for network interfaces is stored in /etc/network/interfaces for Debian Linux distributions and its derivatives or ifcfg files in /etc/sysconfig/network-scripts/ for Fedora and its derivatives, and DNS-servers in /etc/resolv.conf. /etc/network/interfaces or /etc/sysconfig/network-scripts/ifcfg-* can define a static IP-address or dhclient to be used, and all kinds of VPN can be configured here as well. In case the configuration has to be changed, DHCP-protocol goes a long way to do so automatically, without the user even noticing.