The ip command is a versatile tool that can be used to configure and manage various aspects of the network interfaces, such as IP addresses, routes, tunnels, and more. Depending on the options and arguments used, the ip command can cause different changes to the network configuration. Some of the possible changes are:
Network interfaces may become active or inactive. The ip command can be used to bring up or down a network interface, which means to activate or deactivate its connection to the network. For example, the command ip link set eth0 up will bring up the interface eth0, while the command ip link set eth0 down will bring it down. This can affect the network connectivity and performance of the system.
IP addresses may change. The ip command can be used to assign or remove IP addresses to a network interface, which are the numerical identifiers that allow the system to communicate with other hosts in the network. For example, the command ip addr add 192.168.1.100/24 dev eth0 will assign the IP address 192.168.1.100 with a subnet mask of 255.255.255.0 to the interface eth0, while the command ip addr del 192.168.1.100/24 dev eth0 will remove it. This can affect the network reachability and routing of the system.
The routing table may change. The ip command can be used to add or delete routes to the routing table, which is a data structure that stores the information about how to reach different network destinations. For example, the command ip route add 10.0.0.0/8 via 192.168.1.1 dev eth0 will add a route to the network 10.0.0.0/8 through the gateway 192.168.1.1 using the interface eth0, while the command ip route del 10.0.0.0/8 via 192.168.1.1 dev eth0 will delete it. This can affect the network traffic and efficiency of the system.
The ip command does not affect the following settings:
New name servers may be added to the resolver configuration. The resolver configuration is a file that specifies the name servers that the system uses to resolve domain names to IP addresses. The resolver configuration file is usually /etc/resolv.conf, and it is not modified by the ip command. To add or remove name servers, the file has to be edited manually or by another tool, such as resolvconf or NetworkManager.
The system's host name may change. The host name is a human-readable name that identifies the system in the network. The host name is usually stored in the file /etc/hostname, and it is not changed by the ip command. To change the host name, the file has to be edited manually or by another tool, such as hostnamectl or nmtui.
Reference:
LPIC-1 Exam 102 Objectives, Topic 109: Networking Fundamentals, Subtopic 109.2: Persistent network configuration, Weight: 2, Key Knowledge Areas: Query and modify the behavior of network interfaces. Objective: Use the ip command to configure and modify the behavior of network interfaces.
LPIC-1 Exam 102 Learning Materials, Topic 109: Networking Fundamentals, Subtopic 109.2: Persistent network configuration, Section 109.2.2: ip, Page 17-19.