ip Command

The ip command in Linux is used to display and manipulate routing, network devices, interfaces, and tunnels. It is a powerful utility provided by the iproute2 package and is considered a replacement for the older ifconfig and route commands.

Common Usage

ip [OPTIONS] OBJECT { COMMAND | help }

• OBJECT: Specifies the type of object to manipulate or view (e.g., address, link, route).

• COMMAND: The action to be performed on the object (e.g., add, delete, show).

Common OBJECTs

1. link: Manage network interfaces.

2. addr: Display and configure IP addresses.

3. route: Manipulate the routing table.

4. neigh: Display and manipulate ARP entries (neighbor cache).

5. maddr: Manage multicast addresses.

6. rule: Manage rule-based routing.

7. tunnel: Configure tunnel interfaces (e.g., GRE, IPIP).

Basic Examples

1. Display Network Interfaces (Link)

To view the status of all network interfaces:

ip link show

This will show a list of all network interfaces, including their statuses (up, down), and other information like MTU (Maximum Transmission Unit).

To view a specific interface:

ip link show dev eth0

2. Display IP Addresses

To view all IP addresses configured on the system:

ip addr show

This shows IP addresses for all interfaces, including IPv4 and IPv6 addresses. To view details for a specific interface:

ip addr show dev eth0

3. Assign IP Address to Interface

To assign an IP address to an interface, use the following syntax:

sudo ip addr add 192.168.1.100/24 dev eth0

This command assigns the IP 192.168.1.100 with a subnet mask of 255.255.255.0 to the eth0 interface.

4. Delete an IP Address from Interface

To remove an IP address from an interface:

sudo ip addr del 192.168.1.100/24 dev eth0

5. Bring Interface Up or Down

To bring an interface up (enable it):

sudo ip link set dev eth0 up

To bring an interface down (disable it):

sudo ip link set dev eth0 down

6. Display Routing Table

To view the system's routing table:

ip route show

This will display the routing table entries, including default gateways and other routes.

7. Add a Static Route

To add a new static route to a network:

sudo ip route add 192.168.2.0/24 via 192.168.1.1 dev eth0

This adds a route to the 192.168.2.0/24 network through the gateway 192.168.1.1 using the eth0 interface.

8. Delete a Static Route

To delete a static route:

sudo ip route del 192.168.2.0/24

9. Configure a Default Gateway

To set a default gateway:

sudo ip route add default via 192.168.1.1 dev eth0

This configures 192.168.1.1 as the default gateway for all outbound traffic.

10. Display ARP Cache (Neighbor Entries)

To display the ARP (Address Resolution Protocol) cache:

ip neigh show

11. Flush IP Addresses

To flush all IP addresses on an interface:

sudo ip addr flush dev eth0

Advanced Examples

1. View Multicast Group Memberships

To view the multicast group memberships on an interface:

ip maddr show dev eth0

2. Configure Policy Routing

To add a rule that routes traffic from a specific source IP through a specific table:

sudo ip rule add from 192.168.1.100 table 100

Then, configure the routes for table 100:

sudo ip route add default via 192.168.1.1 dev eth0 table 100

3. Configure Tunnels

To configure a GRE tunnel:

sudo ip tunnel add gre1 mode gre remote 192.168.2.1 local 192.168.1.100 ttl 255
sudo ip link set gre1 up
sudo ip addr add 10.10.10.1/30 dev gre1

This sets up a GRE tunnel between 192.168.1.100 (local) and 192.168.2.1 (remote).

IP Command Syntax Overview

• ip link: Manage network interfaces (view, up/down, configure).

• ip addr: Manage IP addresses (view, add, delete).

• ip route: Manage the routing table (view, add, delete, change).

• ip neigh: Manage neighbor cache (ARP entries).

• ip maddr: Manage multicast addresses.

Conclusion

The ip command provides a versatile and modern way to manage network configurations in Linux. By replacing older utilities such as ifconfig and route, it offers a more consistent and extensible way to handle network interfaces, IP addresses, routes, and tunnels. It is a crucial tool for Linux system administrators and network engineers.