The Linux ip command is a powerful utility for network management. It replaces older networking commands like ifconfig, route, and arp, providing a unified toolset to configure, monitor, and troubleshoot network settings on Linux systems. It’s commonly used for setting up and managing IP addresses, routes, and network interfaces.

Key Usage and Syntax of the ip Command #

The ip command follows a structured syntax:

ip [OPTIONS] OBJECT COMMAND

• OPTIONS include flags for further customization, like -4 for IPv4 or -6 for IPv6.
• OBJECT represents the network item you want to manage, such as link (interface), addr (address), route, etc.
• COMMAND is the action you want to perform, like add, show, delete, or set.

ip Command Cheatsheet Table #

Command	Description
ip link show	List all network interfaces
ip addr show	Show IP addresses for all interfaces
ip addr add <IP>/<subnet> dev <iface>	Add IP address to an interface
ip addr del <IP>/<subnet> dev <iface>	Remove IP address from an interface
ip route show	Display all routing table entries
ip route add <dest> via <gateway>	Add a new route
ip route del <dest>	Delete an existing route
ip neigh show	Display neighbor cache (ARP table)
ip rule show	Show all routing rules
ip rule add from <IP>/<prefix> table <table-id>	Add a rule to route from a specific source using a table
ip rule del from <IP>/<prefix> table <table-id>	Delete a rule based on source IP

The ip addr Subcommand #

The ip addr command displays and manages IP addresses for network interfaces.

Show #

ip addr show

Example Output #

This command lists each network interface with details such as IP address, subnet mask, broadcast address, and link state. Here’s an example:

2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:1a:02:50 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.10/24 brd 192.168.1.255 scope global dynamic enp0s3
valid_lft 86320sec preferred_lft 86320sec
inet6 fe80::a00:27ff:fe1a:250/64 scope link
valid_lft forever preferred_lft forever

Explanation of the Output #

• Interface Info: The line starting with 2: enp0s3 shows the network interface name (enp0s3), along with flags like BROADCAST, MULTICAST, UP, LOWER_UP, indicating the interface supports broadcast and multicast and is up and running.
• MAC Address: The link/ether line displays the MAC address (08:00:27:1a:02:50) of the interface.
• IPv4 Address: The inet line provides the IPv4 address (192.168.1.10/24) assigned to the interface, with /24 indicating the subnet mask.
• IPv6 Address: The inet6 line lists the IPv6 address (fe80::a00:27ff:fe1a:250), if available.

This command is essential for checking network interfaces’ IP addresses and their status.

Add #

Assign an IP Address to a Network Interface

ip addr add 192.168.1.100/24 dev enp0s3

Output

This command doesn’t provide output if successful, which is common in Linux for configuration commands. If there’s an issue (e.g., an IP conflict), it will display an error message.

Delete #

Remove an IP Address from an Interface

ip addr del 192.168.1.100/24 dev enp0s3

Output
Similar to add, this command is silent on success. You would only see output if the IP address isn’t assigned to the specified interface or if there’s another error.

Flush #

Clear All IP Addresses from an Interface
ip addr flush dev enp0s3

Output
This command gives no output on success. It’s typically used to reset the IP configuration of an interface.

The ip route Subcommand #

The ip route command manages routing entries in the kernel’s IP routing table, specifying where packets should be forwarded.

Show #

Display the Routing Table

ip route show

Example Output

default via 192.168.1.1 dev enp0s3 proto static
192.168.1.0/24 dev enp0s3 proto kernel scope link src 192.168.1.10

Explanation of the Output

• default via: Indicates the default route, pointing to the gateway IP (192.168.1.1) for outgoing traffic.
• 192.168.1.0/24 dev enp0s3: Shows a route to the local subnet, handled by the enp0s3 interface with 192.168.1.10 as the source address.

Add #

Create a New Route
ip route add 10.0.0.0/24 via 192.168.1.1 dev enp0s3


Output
This command adds a route to the 10.0.0.0/24 subnet, routing traffic through 192.168.1.1 via enp0s3. It won’t display any output on success.

Delete #

Remove a Route

ip route del 10.0.0.0/24

Output
Removes the specified route, with no output if it succeeds.

Flush #

Clear Routing Table Entries
ip route flush dev enp0s3

Output
Flushes all routes for enp0s3, typically used for reconfiguration or troubleshooting.

The ip rule Subcommand #

Show #

List All Routing Rules
ip rule show

Example Output

0:	from all lookup local
32766:	from all lookup main
32767:	from all lookup default

Explanation of the Output
Each line shows a rule with a priority number (e.g., 0, 32766). These rules determine which routing table (local, main, or default) to use for different types of traffic.

Add #

Define a New Routing Rule

ip rule add from 192.168.1.100/32 table 100

Output
This rule directs traffic originating from 192.168.1.100 to consult table 100 for routing. There is no output if the command succeeds.

Delete #

Remove a Specific Rule
ip rule del from 192.168.1.100/32 table 100

Output
Deletes the specified rule, with no output if successful.

The ip link Subcommand #

Show #

Display Link Layer Information
ip link show

Example Output

2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether 08:00:27:1a:02:50 brd ff:ff:ff:ff:ff:ff

Explanation of the Output

• Interface Info: Shows the interface name (enp0s3), flags (like UP), and other parameters like MTU (1500).
• link/ether: Displays the MAC address (08:00:27:1a:02:50).

Set: Configure Interface Parameters #

ip link set dev enp0s3 up

Output

Sets the interface enp0s3 to up, activating it without displaying any output on success.

Add #

Create a Virtual Link (e.g., VLAN)
ip link add link enp0s3 name enp0s3.10 type vlan id 10

Output

Creates a VLAN with ID 10 associated with enp0s3. No output indicates the command succeeded.

Delete: Remove a Virtual Link #

ip link del dev enp0s3.10

Output
Deletes the specified virtual link (enp0s3.10) with no output if the operation is successful.

Examples of Using the ip Command #

Display Detailed Interface Information #

To view all available network interfaces with their IP addresses, states, and additional details:

ip addr show

This displays information like IP address, subnet mask, broadcast address, and interface state. You can specify a particular interface, like ip addr show eth0, to see details for a single interface.

Add and Remove IP Addresses #

To assign an IP address to a network interface:

ip addr add 192.168.1.10/24 dev eth0

This command assigns the IP 192.168.1.10 with a subnet mask of /24 to eth0. This is useful for configuring interfaces or adding virtual IPs on a load balancer for high availability.

To remove an IP address from an interface:
ip addr del 192.168.1.10/24 dev eth0

Configuring a Static Route #

To add a static route, which is essential for directing traffic to specific networks:

ip route add 192.168.2.0/24 via 192.168.1.1

This sets a route for the 192.168.2.0/24 network, directing packets through the 192.168.1.1 gateway.

Configuring IP Neighbor Entries (ARP Table) #

To add a permanent entry to the ARP table:

ip neigh add 192.168.1.5 lladdr 00:11:22:33:44:55 dev eth0

This manually maps the IP address 192.168.1.5 to the MAC address 00:11:22:33:44:55 on eth0.

To delete an ARP entry:

ip neigh del 192.168.1.5 dev eth0

Using ip rule for Advanced Routing #

The ip rule object in the ip command is used for policy-based routing, allowing you to set rules that direct packets differently based on source, destination, or other packet attributes. This is especially useful in advanced network setups where multiple routing tables are required, such as multi-homed setups or specific routing policies for certain IP ranges.

For example, to add a rule that routes all packets from a specific source IP (192.168.1.100) using a custom routing table (table 100):

ip rule add from 192.168.1.100/32 table 100

To route traffic to a specific destination using a different table:
ip rule add to 10.10.0.0/24 table 100

To view all rules:
ip rule show

Using the ip Command with RELIANOID Load Balancer #

In RELIANOID’s load balancer environment, the ip command can be instrumental for network configuration and optimization. Here’s how you can use it effectively:

Assigning Virtual IPs #

On a RELIANOID load balancer, virtual IP addresses are crucial for load distribution and high availability. Use the following to assign a VIP:

ip addr add 10.10.10.1/24 dev eth0

This creates a virtual IP on the primary interface, helping distribute client requests across multiple backend servers.

Route Management for Backend Communication #

To ensure that the load balancer forwards traffic to backend servers on a specific subnet, configure a static route:

ip route add 10.10.20.0/24 via 10.10.10.2

This configuration ensures traffic destined for 10.10.20.0/24 is correctly routed through the specified gateway.

Monitoring Network Interface Stats #

Checking interface statistics is helpful for monitoring traffic load and troubleshooting. For example:

ip -s link show eth0
This command provides real-time stats on packet transmission, errors, and drops on the eth0 interface, which can help monitor load and adjust balancing settings as needed.

Using the ip command, RELIANOID’s load balancer can maintain efficient network configuration, manage IP addresses and routes dynamically, and provide a robust foundation for secure and optimized traffic handling.

Summary #

In summary, the Linux ip command is a versatile and essential tool for network configuration and management, allowing fine-grained control over interfaces, routes, and policies. Its flexibility enables efficient handling of complex network setups, like those in load balancer environments, by allowing administrators to manage IP addresses, define routes, and implement policy-based rules. For RELIANOID load balancers, leveraging the ip command ensures robust traffic management, optimized routing, and a resilient architecture ready for high availability and efficient load distribution.