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Linux · NetworkingBeginner

Linux: Inspect Addresses and Bring a Link Up

An Ethernet interface has the correct address but is administratively down. Read link and address state, then bring it up. Work through it yourself in the live host terminal below.

Interactive simLinuxiproute2InterfacesBeginner-friendly

Symptom

An Ethernet interface has the correct address but is administratively down. Read link and address state, then bring it up.

Your mission

Inspect, recover, then verify

Format

Linux shell

Start interactive labSee the investigation plan ↓Need a hint? Reveal the root cause ↓
Linux: Inspect Addresses and Bring a Link Up

Investigate before you configure.

Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.

Observe the symptom and link state.

Diagnose by comparing the protocol evidence.

Verify the expected device state and confirm the original symptom is resolved.

Console access: Linux

This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.

Need a hint?

Reveal the root cause when you're ready.

Try the investigation first, then use this as your escape hatch, not a dead end.

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Lab debrief

Turn the session into a repeatable troubleshooting pattern.

Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.

The problem

`enp0s3` is configured with 10.20.30.114/24 but cannot send traffic because its link flags lack UP.

What you'll practice

  • Use ip -brief link for concise link state
  • Use ip -brief address for assigned prefixes
  • Distinguish administrative DOWN from address configuration
  • Bring one interface up with ip link set

The topology

One Ubuntu host has loopback and Ethernet enp0s3. The Ethernet cable is connected, but the interface is administratively down.

Commands to run yourself

The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.

Show link state
ip -brief link
Show addresses
ip -brief address

Topology diagram

Fact-checked references

The commands and behaviour in this lab were checked against these primary references.

Frequently asked

Is this change persistent after reboot?

No. The ip command changes live kernel state. Use the host's persistent network manager for a durable configuration.

What is LOWER_UP?

It indicates the driver reports the lower-layer link as operational, such as Ethernet carrier being present.

Ready to run this lab yourself?

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