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Vultr profile image Sanskriti Harmukh
Sanskriti Harmukh for Vultr

Posted on with Aashish Chaurasiya Originally published at docs.vultr.com

Using the Linux IP Command to Manage Server Network Interfaces

#linux #networking #cli #sysadmin

The ip command is a built-in Linux network management utility that offers a wide range of features and tools for managing network interfaces. It's an improved utility that combines the functionality of legacy commands such as ifconfig, arp, and route into a single tool for managing, monitoring, and troubleshooting your server's network interfaces. This guide covers using the ip command to manage ip objects such as links, addresses, routes, and neighbors, including interface configuration, static routing, enabling/disabling interfaces, and MTU management. By the end, you'll be able to inspect, configure, and troubleshoot your server's network interfaces using the ip command.

Prerequisites

Before you begin, you need to:

  • Deploy an Ubuntu 24.04 server instance to test the ip command functionalities.
  • Attach the server to a VPC network.
  • Access the server using SSH as a non-root user with sudo privileges.

How to Use the IP Command

The ip command uses the following syntax to manage network information and interfaces on your server.

$ ip [OPTIONS] OBJECT COMMAND [ARGUMENTS]
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Within the above command:

  • OPTIONS: Sets the ip command operation mode.
  • OBJECT: Specifies the type of network object to view or manage. For example, link, address, route.
  • COMMAND: Defines the action to perform on the specified object. For example, add, del, show.
  • ARGUMENTS: Sets additional options to execute with the command.

View Network Interface Information

The ip command displays network interface information at varying levels of detail depending on the object and options used.

1. View information about all network interfaces available on the server:

$ ip link show
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Your output should be similar to the one below.

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 56:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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Based on the above output, the command displays the total number of available interfaces, the MTU value, state, and MAC address for each interface. Active interfaces use the UP state while inactive interfaces use the DOWN state. Interfaces with a DOWN state cannot send or receive network traffic on the server unless enabled.

2. Display network interfaces in an active and running state:

$ ip link show up
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Output:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 56:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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3. Use the -br option to display only important information about the network interfaces:

$ ip -br link show
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Output:

lo               UNKNOWN        00:00:00:00:00:00 <LOOPBACK,UP,LOWER_UP> 
enp1s0           UP             56:00:04:ef:40:23 <BROADCAST,MULTICAST,UP,LOWER_UP> 
enp8s0           UP             5a:00:04:ef:40:23 <BROADCAST,MULTICAST,UP,LOWER_UP>
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4. Use the addr option, or its a shorthand, to view full information including IP addresses on all network interfaces:

$ ip a
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Your output should look like the one below.

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 56:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    inet 192.0.2.100/23 brd 192.0.2.255 scope global dynamic enp1s0
       valid_lft 78163sec preferred_lft 78163sec
    inet6 2a05:f480:2c00:1ef7:5400:4ff:feef:4023/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591891sec preferred_lft 604691sec
    inet6 fe80::5400:4ff:feef:4023/64 scope link 
       valid_lft forever preferred_lft forever
3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    inet 10.50.112.3/20 brd 10.50.127.255 scope global enp8s0
       valid_lft forever preferred_lft forever
    inet6 fe80::5800:4ff:feef:4023/64 scope link 
       valid_lft forever preferred_lft forever
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5. View specific information about a specific network interface. For example, view information about the VPC interface, enp8s0:

$ ip addr show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    inet 10.50.112.3/20 brd 10.50.127.255 scope global enp8s0
       valid_lft forever preferred_lft forever
    inet6 fe80::5800:4ff:feef:4023/64 scope link 
       valid_lft forever preferred_lft forever
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6. View detailed statistics about a specific network interface. For example, enp8s0:

$ ip -s link show enp8s0
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Your output should be similar to the one below.

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    RX:  bytes packets errors dropped  missed   mcast
      25426631   61808      0       0       0       0
    TX:  bytes packets errors dropped carrier collsns
       4351567   40677      0       0       0       0
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Manage Interface IP Addresses Using the IP Command

IP addresses can be assigned to network interfaces using the Dynamic Host Configuration Protocol (DHCP) or static addressing to enable network connections on the interface. DHCP is the default address assignment protocol on most servers, but static IP addressing may be required when working with multiple addresses or new interfaces on your server.

1. Add a new IP address on your network interface. Replace enp8s0 with your desired interface name:

$ sudo ip addr add 192.168.1.10/24 dev enp8s0
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The above command adds a new private network address 192.168.1.10 to the enp8s0 interface. Depending on your addressing scheme, the interface can run with multiple IP addresses that offer different functions or services on your server.

2. View the interface information to verify that the new IP address is available:

$ ip addr show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    inet 10.50.112.3/20 brd 10.50.127.255 scope global enp8s0
       valid_lft forever preferred_lft forever
    inet 192.168.1.10/24 scope global enp8s0
       valid_lft forever preferred_lft forever
    inet6 fe80::5800:4ff:feef:4023/64 scope link 
       valid_lft forever preferred_lft forever
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When using multiple IP addresses, you may need to configure routing to enable specific network connections to use the interface IP address.

3. Use the del option to remove IP addresses on network interfaces. For example, remove the 192.168.1.10/24 address on the enp8s0 interface:

$ sudo ip addr del 192.168.1.10/24 dev enp8s0
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4. View the interface address information to verify that the address is removed:

$ ip addr show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
    inet 10.50.112.3/20 brd 10.50.127.255 scope global enp8s0
       valid_lft forever preferred_lft forever
    inet6 fe80::5800:4ff:feef:4023/64 scope link 
       valid_lft forever preferred_lft forever
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Configure Static Routing Using the IP Command

Static routing directs traffic to remote networks through a specific network interface or IP address as the next hop to reach the network. Network requests to unmatched destinations are directed through the default route via the main server interface, while requests to unknown routes may fail due to missing route information.

1. View the default IP routing table:

$ ip route show
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Your output should be similar to the one below.

default via 192.0.2.100 dev enp1s0 proto dhcp src 192.0.2.100 metric 100 
10.50.112.0/20 dev enp8s0 proto kernel scope link src 10.50.112.3 
192.0.2.0/23 dev enp1s0 proto kernel scope link src 192.0.2.100 
169.254.169.254 via 192.0.2.100 dev enp1s0 proto dhcp src 192.0.2.100 metric 100
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Based on the above output, direct network addresses use the dev option while non-linked addresses use the via option to direct network traffic using the specified address as the next hop. The default route handles all unknown routes on the server unless specified in the routing table.

2. Add a new static route to a remote network such as 10.0.0.0/16 accessible through a server on the VPC network at 10.50.112.4 as the next hop:

$ sudo ip route add 10.0.0.0/16 via 10.50.112.4
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3. View the routing table again to verify that the new route is available:

$ ip route show
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Output:

default via 192.0.2.100 dev enp1s0 proto dhcp src 192.0.2.100 metric 100 
10.0.0.0/16 via 10.50.112.4 dev enp8s0 
10.50.112.0/20 dev enp8s0 proto kernel scope link src 10.50.112.3 
192.0.2.0/23 dev enp1s0 proto kernel scope link src 192.0.2.100 
169.254.169.254 via 192.0.2.100 dev enp1s0 proto dhcp src 192.0.2.100 metric 100
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Enable or Disable Network Interfaces

Disabling a network interface stops it from sending or receiving traffic without removing its configuration, which is useful for maintenance or troubleshooting.

1. Use the ip link set command to disable the enp8s0 interface:

$ sudo ip link set dev enp8s0 down
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2. View the network interface status and verify that the state is DOWN:

$ ip link show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST> mtu 1450 qdisc mq state DOWN mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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3. Enable the network interface:

$ sudo ip link set dev enp8s0 up
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4. View the interface information to verify the new status:

$ ip link show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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Managing the Network Interface MTU (Maximum Transmission Unit)

MTU is the maximum size of a packet in bytes that can be transmitted over a network interface without fragmentation. The default MTU value on most network interfaces is 1500. Depending on your needs, you may modify the value to allow the transfer of large or small data packets on private networks such as a VPC network.

1. View your target interface MTU value. For example, the VPC interface enp8s0:

$ ip link show enp8s0
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2. Verify the MTU value in your output, similar to the one below:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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3. Set a new MTU value on the interface. For example, 3000, to transfer large data packets and improve efficiency with other servers in the VPC network:

$ sudo ip link set dev enp8s0 mtu 3000
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4. View the interface information again and verify the new MTU value:

$ ip link show enp8s0
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Output:

3: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 3000 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 5a:00:04:ef:40:23 brd ff:ff:ff:ff:ff:ff
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Next Steps

  • Use ip neigh to inspect and manage the ARP/neighbor table on your server.
  • Persist static routes and IP addresses in your distribution's network configuration so they survive a reboot.
  • Combine ip -br output with a monitoring script to alert on interfaces that drop to a DOWN state.
  • Run man ip for the full list of ip objects and commands beyond what's covered here.

For the full guide with additional tips, visit the original article on Vultr Docs.

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