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

Resources

• TCP/IP Guide

• Mozilla SSL Config