IP Network Interface

IP Network Interface Troubleshooting for Beginners

Table of Contents

1. 📝 What is ip?
2. ⚡ Basic Commands
   • Show All Network Interfaces
   • Show Specific Interface
   • Show Link Information
   • Show Routing Table
3. 🔧 Interface Management
   • Bring Interface Up
   • Bring Interface Down
   • Add IP Address to Interface
   • Remove IP Address from Interface
4. 💡 Common Troubleshooting

• Check Interface Status
• Verify IP Address
• Check Default Gateway
• Test Connectivity

17. ⌨️ Quick Reference

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📝 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

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⚡ 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

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Show Specific Interface

ip addr show enp6s0

Short form:

ip a show enp6s0

Shows information for a specific network interface.

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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

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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)

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🔧 Interface Management

Bring Interface Up

sudo ip link set enp6s0 up

What this does:

• Activates a network interface
• Brings interface online

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Bring Interface Down

sudo ip link set enp6s0 down

What this does:

• Deactivates a network interface
• Takes interface offline

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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)

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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

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💡 Common Troubleshooting

Check Interface Status

ip link show enp6s0

Look for state UP or state DOWN.

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Verify IP Address

ip addr show enp6s0

Check if interface has an IP address assigned.

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Check Default Gateway

ip route show

Look for default via entry.

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Test Connectivity

ping -c 4 8.8.8.8

Tests internet connectivity.

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⌨️ 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

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For network connections, see the SS Network Troubleshooting Guide.