125 lines
4.1 KiB
Markdown
125 lines
4.1 KiB
Markdown
# Linux Network Troubleshooting Guide
|
|
|
|
## 1. Basic Network Configuration Check:
|
|
|
|
- Check IP address and network interface status:
|
|
- `ip addr show` # This command displays all network interfaces, their IP addresses, and status.
|
|
|
|
- Verify default gateway:
|
|
- `ip route show` # Ensures your system knows how to route traffic outside the local network.
|
|
|
|
- Check DNS configuration:
|
|
- `cat /etc/resolv.conf` # Displays the DNS servers your system is using.
|
|
|
|
## 2. Connectivity Tests:
|
|
|
|
- Ping test:
|
|
- `ping -c 4 8.8.8.8` # Tests basic connectivity to Google's DNS server (or any other IP). Only pings 4 times (-c 4)
|
|
|
|
- Traceroute:
|
|
- `traceroute google.com` # Shows the path packets take to reach a destination.
|
|
|
|
- DNS resolution test:
|
|
- `nslookup google.com` # These test DNS resolution capabilities.
|
|
- `dig google.com` # These test DNS resolution capabilities.
|
|
|
|
## 3. Advanced Diagnostic Tools:
|
|
|
|
- netstat or ss:
|
|
- `netstat -tulpn` # Display active network connections and listening ports.
|
|
- `ss -tulpn` # Display active network connections and listening ports.
|
|
|
|
- tcpdump:
|
|
- `sudo tcpdump -i eth0` # eth0 is the Device name. Captures and displays packet data on a specified interface.
|
|
|
|
- nmap:
|
|
- `nmap -p- localhost` # Scans every port on the local machine (or any specified target).
|
|
|
|
## 4. Firewall Configuration:
|
|
|
|
- Check iptables rules:
|
|
- `sudo iptables -L -v -n` # Displays current firewall rules.
|
|
|
|
- Temporarily disable firewall (for testing):
|
|
- `sudo systemctl stop firewalld` # Stops firewalld on the current boot - will start at next boot if enabled
|
|
- `sudo ufw disable` # Disables firewalld at system boot and stops it immedietely
|
|
|
|
## 5. Network Service Diagnostics:
|
|
|
|
- Check service status:
|
|
- `systemctl status networking`
|
|
- `systemctl status NetworkManager`
|
|
|
|
- Restart network service:
|
|
- `sudo systemctl restart networking`
|
|
- `sudo systemctl restart NetworkManager`
|
|
|
|
## 6. Network Interface Configuration:
|
|
|
|
- Edit network interface configuration:
|
|
- `sudo nano /etc/network/interfaces` # for Debian-based systems
|
|
- `sudo nano /etc/sysconfig/network-scripts/ifcfg-eth0` # for Red Hat-based systems
|
|
|
|
- Restart specific network interface:
|
|
- `sudo ifdown eth0 && sudo ifup eth0`
|
|
- `sudo ip link set eth0 down && sudo ip link set eth0 up`
|
|
|
|
## 7. Wireless Network Troubleshooting:
|
|
|
|
- List available wireless networks:
|
|
- `sudo iwlist wlan0 scan`
|
|
|
|
- Check wireless interface details:
|
|
- `iwconfig`
|
|
|
|
- Monitor wireless connection in real-time:
|
|
- `watch -n 1 iwconfig`
|
|
|
|
## 8. Advanced Network Analysis:
|
|
|
|
- Wireshark: GUI-based packet analyzer
|
|
Install with:
|
|
- `sudo apt-get install wireshark` # on Debian-based systems
|
|
- `sudo yum install wireshark` # on Red Hat-based systems
|
|
|
|
- iftop: Displays bandwidth usage on an interface
|
|
- `sudo iftop -i eth0`
|
|
|
|
- nethogs: Groups bandwidth by process
|
|
- `sudo nethogs eth0`
|
|
|
|
## 9. Performance Testing:
|
|
|
|
- iperf: Network performance measurement tool
|
|
- `iperf -s` # on server
|
|
- `iperf -c server_ip` # on client
|
|
|
|
|
|
- speedtest-cli: Command-line interface for testing internet speed
|
|
`speedtest-cli`
|
|
|
|
## 10. Log Analysis:
|
|
- `sudo tail -f /var/log/syslog` # on Debian-based systems
|
|
- `sudo tail -f /var/log/messages` # on Red Hat-based systems
|
|
- `sudo journalctl -b0`
|
|
- `sudo dmesg -k`
|
|
|
|
- Network-specific logs:
|
|
- `sudo tail -f /var/log/daemon.log`
|
|
|
|
## 11. Network Configuration Backup and Restore:
|
|
|
|
- Backup network configuration:
|
|
- `sudo tar -czvf network_config_backup.tar.gz /etc/network` # Create a file called network_config_backup.tar.gz from the /etc/network directory
|
|
|
|
- Restore network configuration:
|
|
- `sudo tar -xzvf network_config_backup.tar.gz -C /`
|
|
|
|
## 12. Troubleshooting Specific Issues:
|
|
|
|
- High latency: Use ping and traceroute to identify where delays occur.
|
|
- Packet loss: Use mtr (My TraceRoute) for a combination of ping and traceroute.
|
|
- DNS issues: Check /etc/hosts file and DNS server configurations.
|
|
- IP conflicts: Use arping to detect duplicate IP addresses on the network.
|
|
|