majiayu000 Networking Skill
Overview
Master networking fundamentals for DevOps infrastructure management.
Parameters
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
| protocol | string | No | all | Protocol focus |
| operation | string | Yes | - | Operation type |
Core Topics
MANDATORY
- TCP/IP and OSI model
- DNS configuration and troubleshooting
- HTTP/HTTPS and TLS
- SSH key management and tunneling
- Firewall basics (iptables, ufw)
OPTIONAL
- Load balancing
- VPN and tunneling
- Traffic analysis with tcpdump
ADVANCED
- BGP and routing protocols
- SDN concepts
- Zero-trust networking
Quick Reference
# DNS
dig +trace example.com
dig @8.8.8.8 example.com
host -t MX example.com
# TCP/IP Diagnostics
ping -c 4 host
traceroute host
ss -tuln
ip addr show
# HTTP Testing
curl -I https://example.com
curl -v https://example.com
# SSL/TLS
openssl s_client -connect host:443
openssl x509 -in cert.pem -text -noout
# SSH
ssh-keygen -t ed25519
ssh-copy-id user@host
ssh -L 8080:localhost:80 user@host
ssh -D 1080 user@host
# Firewall (UFW)
ufw status verbose
ufw allow 22/tcp
ufw deny from 192.168.1.100
# Firewall (iptables)
iptables -L -n -v
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
Troubleshooting
Common Failures
| Symptom | Root Cause | Solution |
|---|---|---|
| Connection refused | Service not running | Check ss -tuln |
| Connection timeout | Firewall/routing | Check firewall, traceroute |
| Name resolution failed | DNS issue | Check /etc/resolv.conf |
| Certificate error | Expired/invalid cert | Check dates, verify chain |
Debug Checklist
- Layer 1-2: Link up?
ip link show - Layer 3: Ping gateway?
- Layer 4: Port open?
ss -tuln - DNS: Resolving?
dig hostname - Firewall: Allowing?
iptables -L
Recovery Procedures
Lost SSH Access
- Use cloud console/IPMI
- Check sshd:
sshd -t - Verify firewall:
iptables -L -n