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

1. Layer 1-2: Link up? ip link show
2. Layer 3: Ping gateway?
3. Layer 4: Port open? ss -tuln
4. DNS: Resolving? dig hostname
5. Firewall: Allowing? iptables -L

Recovery Procedures

Lost SSH Access

1. Use cloud console/IPMI
2. Check sshd: sshd -t
3. Verify firewall: iptables -L -n

Resources

• TCP/IP Guide
• Mozilla SSL Config