2bfbc7bb77
- Created structured documentation with /patterns/, /examples/, and /reference/ directories - Implemented automatic context loading rules in CLAUDE.md based on file extensions, directories, and keywords - Added technology-specific patterns for Docker, Python, Node.js, Vue.js, Bash, networking, databases, and VM management - Included complete working examples for common workflows and troubleshooting references - Designed for minimal context usage with precise loading triggers 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>
3.1 KiB
3.1 KiB
Network Troubleshooting Reference
Connectivity Issues
Basic connectivity tests
# Test connectivity
ping <target_ip>
ping -c 4 <target_ip> # Linux (4 packets)
# Test specific port
telnet <target_ip> <port>
nc -zv <target_ip> <port> # netcat
nmap -p <port> <target_ip>
# DNS resolution
nslookup <hostname>
dig <hostname>
host <hostname>
Network interface debugging
# Show interfaces
ip addr show
ifconfig
# Show routing table
ip route
route -n
# Show network statistics
netstat -i
ss -i
Service Issues
Port and process debugging
# Show listening ports
netstat -tulpn
ss -tulpn
lsof -i :<port>
# Find process using port
fuser <port>/tcp
lsof -i tcp:<port>
# Show all connections
netstat -an
ss -an
Service status
# Systemd services
systemctl status <service>
systemctl is-active <service>
systemctl is-enabled <service>
# Service logs
journalctl -u <service> -f
journalctl -u <service> --since "1 hour ago"
Firewall Debugging
iptables
# List rules
iptables -L -n -v
iptables -t nat -L -n -v
# Check if rule exists
iptables -C INPUT -p tcp --dport 80 -j ACCEPT
# Temporarily disable firewall
systemctl stop iptables # CentOS/RHEL
ufw disable # Ubuntu
UFW (Ubuntu)
# Check status
ufw status verbose
# Show rules by number
ufw status numbered
# Check logs
tail -f /var/log/ufw.log
SSL/TLS Issues
Certificate debugging
# Check certificate details
openssl x509 -in certificate.crt -text -noout
openssl s_client -connect <hostname>:443 -servername <hostname>
# Check certificate chain
openssl s_client -connect <hostname>:443 -showcerts
# Test SSL connection
curl -vI https://<hostname>
wget --no-check-certificate -O /dev/null https://<hostname>
Certificate expiration
# Check expiration date
openssl x509 -in certificate.crt -enddate -noout
# Check remote certificate expiration
echo | openssl s_client -servername <hostname> -connect <hostname>:443 2>/dev/null | openssl x509 -noout -dates
DNS Issues
DNS server testing
# Test specific DNS server
nslookup <hostname> <dns_server>
dig @<dns_server> <hostname>
# Flush DNS cache
# Linux (systemd-resolved)
systemctl restart systemd-resolved
# Linux (nscd)
systemctl restart nscd
DNS configuration
# Check DNS settings
cat /etc/resolv.conf
cat /etc/systemd/resolved.conf
# Test DNS resolution order
getent hosts <hostname>
Performance Issues
Bandwidth testing
# iperf3 testing
# Server: iperf3 -s
# Client: iperf3 -c <server_ip>
# wget speed test
wget -O /dev/null http://speedtest.tele2.net/100MB.zip
Network latency
# Continuous ping with timestamps
ping -D <target>
# MTR (better than traceroute)
mtr <target>
mtr --report <target>
Quick Diagnostics
One-liner network check
# Basic network health
ping -c 1 8.8.8.8 && echo "Internet OK" || echo "No Internet"
# Service accessibility
nc -zv localhost 80 && echo "HTTP service running" || echo "HTTP service down"
Network interface stats
# Interface statistics
cat /proc/net/dev
watch -n 1 cat /proc/net/dev