IP Network Interface - ryzendew/Linux-Tips-and-Tricks GitHub Wiki

IP Network Interface Troubleshooting for Beginners

Table of Contents

  1. :pencil: What is ip?
  2. :zap: Basic Commands
  3. :wrench: Interface Management
  4. :bulb: Common Troubleshooting
  1. :keyboard: Quick Reference

:pencil: What is ip?

  • ip is the modern replacement for older network commands like ifconfig, route, and arp
  • Part of the iproute2 package (usually pre-installed)
  • More powerful and feature-rich than legacy commands
  • Used for configuring and troubleshooting network interfaces

What ip can do:

  • Show network interface information
  • Configure IP addresses
  • Manage routing tables
  • Show network statistics
  • Troubleshoot network connectivity

:zap: Basic Commands

Show All Network Interfaces

ip addr show

Short form:

ip a

What this does:

  • Shows all network interfaces and their IP addresses
  • Displays interface status (UP/DOWN)
  • Shows IPv4 and IPv6 addresses

Example output:

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 noprefixroute 
       valid_lft forever preferred_lft forever
2: enp6s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether ec:75:0c:66:f1:7b brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.152/24 brd 192.168.2.255 scope global dynamic noprefixroute enp6s0
       valid_lft 231092sec preferred_lft 231092sec
    inet6 fe80::ee75:cff:fe66:f17b/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

What it shows:

  • Interface name (lo, enp6s0, etc.)
  • Interface state (UP/DOWN)
  • MAC address (link/ether)
  • IP addresses (inet for IPv4, inet6 for IPv6)
  • Network mask and broadcast address

Show Specific Interface

ip addr show enp6s0

Short form:

ip a show enp6s0

Shows information for a specific network interface.

Show Link Information

ip link show

Short form:

ip l

What this does:

  • Shows link layer information (Layer 2)
  • Displays interface status and MAC addresses
  • Shows if interface is UP or DOWN

Example 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: enp6s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether ec:75:0c:66:f1:7b brd ff:ff:ff:ff:ff:ff

Show Routing Table

ip route show

Short form:

ip r

What this does:

  • Shows the routing table
  • Displays default gateway
  • Shows network routes

Example output:

default via 192.168.2.1 dev enp6s0 proto dhcp src 192.168.2.152 metric 100 
192.168.2.0/24 dev enp6s0 proto kernel scope link src 192.168.2.152 metric 100

What it shows:

  • Default route (default via)
  • Network routes (192.168.2.0/24)
  • Interface used (dev)
  • Source IP (src)

:wrench: Interface Management

Bring Interface Up

sudo ip link set enp6s0 up

What this does:

  • Activates a network interface
  • Brings interface online

Bring Interface Down

sudo ip link set enp6s0 down

What this does:

  • Deactivates a network interface
  • Takes interface offline

Add IP Address to Interface

sudo ip addr add 192.168.1.100/24 dev enp6s0

What this does:

  • Adds an IP address to an interface
  • /24 is the subnet mask (255.255.255.0)

Remove IP Address from Interface

sudo ip addr del 192.168.1.100/24 dev enp6s0

What this does:

  • Removes an IP address from an interface

:bulb: Common Troubleshooting

Check Interface Status

ip link show enp6s0

Look for state UP or state DOWN.

Verify IP Address

ip addr show enp6s0

Check if interface has an IP address assigned.

Check Default Gateway

ip route show

Look for default via entry.

Test Connectivity

ping -c 4 8.8.8.8

Tests internet connectivity.

:keyboard: Quick Reference

ip a                    # Show all addresses
ip a show enp6s0        # Show specific interface
ip l                    # Show all links
ip r                    # Show routing table
sudo ip link set enp6s0 up    # Bring interface up
sudo ip link set enp6s0 down  # Bring interface down

For network connections, see the SS Network Troubleshooting Guide.