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Network issues typically manifest as the following problems:
▪ Website inaccessible
▪ Application response is slow
▪ Intermittent connection drops
▪ Data transfer timeouts
Focus: How to quickly locate the problem?
Diagnostic Process
Step 1: Basic Connectivity Check (ping command)
# Check local loopback ping 127.0.0.1
# Check gateway connectivity ping $(ip route | grep default | awk '{print $3}')
# Check DNS resolution ping baidu.com ping 8.8.8.8Diagnostic Key Points:
🔹 Packet loss rate exceeding 5% needs attention
🔹 Latency exceeding 100ms may indicate network congestion
🔹 Unable to ping the gateway indicates a local network configuration issue
Step 2: Route Path Analysis (traceroute)
# Linux system traceroute google.com
# If traceroute is unavailable, use mtr mtr --report --report-cycles 10 google.comOutput Interpretation Tips:
traceroute to google.com (142.250.191.14), 30 hops max, 60 byte packets
1 192.168.1.1 (192.168.1.1) 1.234 ms 1.123 ms 1.456 ms
2 10.0.0.1 (10.0.0.1) 15.678 ms 16.789 ms 17.234 ms
3 * * * (Request timed out)
4 8.8.8.8 (8.8.8.8) 45.123 ms 44.567 ms 43.890 ms🔹 The third hop shows an asterisk: this may indicate a firewall blocking ICMP or device failure
🔹 Sudden increase in latency: this node may be congested
🔹 Continuous timeouts at a hop: focus on troubleshooting that network device
Step 3: Port Connectivity Testing
# Check specific ports telnet target-host 80
nc -zv target-host 443
# Batch port scan nmap -p 80,443,22,3306 target-hostStep 4: DNS Resolution Verification
# View DNS configuration cat /etc/resolv.conf
# Manual DNS query nslookup example.com
dig example.com
# View domain resolution process dig +trace example.com
Diagnostic Tips
1. Network Interface Status Check
# Check network interface status ip addr show
ip link show
# Check network statistics cat /proc/net/dev
ss -tuln # View listening ports2. Firewall Rule Investigation
# iptables rule check iptables -L -n -v
# View connection tracking cat /proc/net/nf_conntrack | grep target-ip3. Route Table Analysis
# View route table ip route show
route -n
# Add temporary route for testing ip route add target-network via gateway-ip
Efficiency Improvement Tools
1. Automated Diagnostic Script
#!/bin/bash
# network-check.sh
TARGET=${1:-"8.8.8.8"}
echo "=== Network Diagnostic Report ==="
echo "Target Address: $TARGET"
echo "Check Time: $(date)"
echo
echo "1. Basic Connectivity Test:"
ping -c 4 $TARGET
echo -e "\n2. Route Path Analysis:"
traceroute $TARGET
echo -e "\n3. DNS Resolution Test:"
snlookup $TARGET
echo -e "\n4. Local Network Configuration:"
ip addr show | grep -A 2 "state UP"2. Monitoring Alert Setup
# Use watch for continuous monitoring
watch -n 5 'ping -c 1 critical-server && echo "OK" || echo "FAILED"'
# Combine with zabbix or prometheus for automated monitoring
Fault Prevention Strategies
1. Network Health Check List
🔹 Regularly check the status of network devices
🔹 Monitor bandwidth usage
🔹 Check DNS resolution performance
🔹 Validate the availability of backup links
🔹 Update network device firmware
2. Automated Monitoring Script
#!/bin/bash
# daily-network-check.sh
HOSTS=("8.8.8.8" "114.114.114.114" "your-critical-server.com")
LOG_FILE="/var/log/network-health.log"
for host in "${HOSTS[@]}"; do
if ping -c 3 $host > /dev/null 2>&1; then
echo "$(date): $host - OK" >> $LOG_FILE
else
echo "$(date): $host - FAILED" >> $LOG_FILE
# Send alert email or SMS
echo "$host is unreachable" | mail -s "Network Alert" [email protected]
fi
done
Conclusion
Network troubleshooting is one of the core skills of operations and maintenance engineers.
Through a standardized diagnostic process:
ping → traceroute → port testing → DNS verification → in-depth analysis
Following this process, you can quickly locate most network issues.
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Campus Address:
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