First check the physical connection and interface status, use ip link to ensure that the network card is enabled and obtains the IP correctly; 2. Verify the IP configuration and subnet settings, and confirm whether the IP address and default route are correct through ip addr and ip route; 3. Test connectivity in steps, ping local loopback, local IP, gateway and external IP in turn to locate the fault layer; 4. Check DNS resolution, check /etc/resolv.conf or use resolvectl to confirm the DNS server configuration, and use nslookup or dig to test domain name resolution; 5. Troubleshoot firewall and service interference, check UFW or firewalld status, temporarily close the firewall if necessary and ensure that network services such as NetworkManager are running normally; 6. Use diagnostic tools such as traceroute, ss and tcpdump to deeply analyze routing paths, connection status and packet flow, and finally gradually troubleshoot problems at all levels of the network stack to solve Linux network failures.

When working in a Linux environment, network connectivity issues can quickly disrupt productivity. Whether you're managing a server or troubleshooting a desktop system, knowing how to diagnose and fix common network problems is essential. Here's a practical guide to identifying and resolving the most frequent network issues in Linux.

1. Check Physical Connectivity and Interface Status

Before diving into complex diagnostics, verify the basics.

• Ensure the network cable is connected (for wired connections) or that Wi-Fi is enabled (on laptops).

  

• Use ip link to check the status of network interfaces:

   ip link show

  Look for your interface (eg, eth0 , enp3s0 , wlan0 ). If it says DOWN , bring it up:

  

   sudo ip link set eth0 up

• If using DHCP, request an IP address:

   sudo dhclient eth0

? Tip: On modern systems, NetworkManager or systemd-networkd may manage interfaces automatically. Avoid manually configuring interfaces if these services are active unless you know what you're doing.

2. Verify IP Configuration and Subnet Settings

Incorrect IP settings are a common source of problems.

• Check your current IP address and subnet:

   ip addr show

  Look for an IP in the expected range (eg, 192.168.xx , 10.xxx ). If you see 169.254.xx , that's a link-local address—indicating no DHCP server responded.

• Confirm routing with:

   ip route show

  You should see a default route like:

   default via 192.168.1.1 dev eth0

  If missing, add it manually (replace with your gateway):

   sudo ip route add default via 192.168.1.1 dev eth0

3. Test Connectivity Step by Step

Use a layered approach to isolate where the failure occurs.

• Test local interface:

   ping 127.0.0.1

  If this fails, TCP/IP stack issues may exist (rare, but possible if misconfigured).

• Ping your own IP:

   ping 192.168.1.100 # Replace with your IP

  If it doesn't respond, there may be a firewall or interface issue.

• Ping the gateway:

   ping 192.168.1.1 # Replace with your router IP

  Failure here suggests a local network or switch issue.

• Test external connectivity:

   ping 8.8.8.8

  If this works but ping google.com fails, the issue is DNS-related.

4. Troubleshoot DNS Resolution

Even with internet access, bad DNS settings can make it seem like you're offline.

• Check your DNS configuration:

   cat /etc/resolv.conf

  You should see lines like:

   nameserver 8.8.8.8
  nameserver 1.1.1.1

  If not, update it temporarily:

   echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

• Test DNS resolution:

   nslookup google.com
  # or
  dig google.com

  If these time out, your DNS server may be unreachable or blocked.

? Note: Some systems use systemd-resolved , which manages DNS dynamically. Use resolvectl status to inspect DNS settings in such cases.

5. Check for Firewall or Service Interference

Firewalls can silently drop packets.

• If using ufw , check status:

   sudo ufw status

• For firewalld (common on RHEL/CentOS):

   sudo firewall-cmd --state
  sudo firewall-cmd --list-all

• Temporarily disable the firewall to test:

   sudo ufw disable
  # or
  sudo systemctl stop firewalld

  ?? Remember to re-enable it afterward.

Also, ensure key services like NetworkManager or systemd-networkd are running:

 sudo systemctl status NetworkManager

Restart if needed:

 sudo systemctl restart NetworkManager

6. Use Diagnostic Tools for Deeper Analysis

When basic steps don't reveal the issue, use advanced tools.

• traceroute or tracepath – See where packets stop:

   traceroute 8.8.8.8
  # or (no root required)
  tracepath 8.8.8.8

• netstat or ss – Check active connections and listening ports:

   ss -tuln

  Look for expected services (eg, SSH on port 22).

• tcpdump – Capture packets to analyze traffic:

   sudo tcpdump -i eth0 icmp

  This helps confirm if packets are being sent/received.

Final Thoughts

Most network issues in Linux stem from misconfigurations, missing routes, or DNS problems. Start simple: check interface status, IP assignment, gateway reachability, and DNS. Use command-line tools like ping , ip , dig , and ss to methodically test each layer.

Automation tools like nmcli (for NetworkManager) or configuration files in /etc/netplan/ (Ubuntu) or /etc/sysconfig/network-scripts/ (RHEL) may also need review depending on your distribution.

Basically, it's about verifying each hop in the network stack—one step at a time.

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