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Networking

Understand the networking concepts every DevOps engineer needs to know.

Core Topics​

  • Networking Commands — Essential tools and commands for network diagnostics
  • Networking Concepts — Fundamental networking principles for DevOps engineers
  • Networking Cheatsheets — Quick reference guides

Learn More​

Network Fundamentals​

Understand TCP/IP stack, DNS, VPCs, routing, firewalls, load balancing, and network security — critical for cloud infrastructure and DevOps roles.

Key Protocols​

  • TCP/UDP — Transport layer protocols
  • DNS — Domain name resolution
  • HTTP/HTTPS — Application layer protocols
  • SSH — Secure shell for remote access
  • ICMP — Ping and traceroute

DevOps Networking Focus​

  • VPC design and management
  • Network security groups and firewalls
  • Load balancer configuration
  • DNS routing and CDN
  • VPN and hybrid networking
  • Container networking

TCP/IP Model Layers​

Application Layer​

  • Defines — TCP/IP application protocols and how host programs interface with transport services
  • Protocols — HTTP, HTTPS, FTP, SMTP, DNS, SSH, Telnet

Transport Layer​

  • Provides — Communication session management between nodes
  • Defines — Service level and connection states
  • Protocols — TCP, UDP, RTP

Internet Layer​

  • Packages — Data into IP datagrams with source/destination addresses
  • Performs — Routing of IP datagrams
  • Protocols — IP, ICMP, ARP, RARP

Network Access Layer​

  • Specifies — Physical data transmission through networks
  • Handles — Electronic signaling by hardware devices
  • Protocols — Ethernet, Frame Relay, PPP

IP Addressing​

IPv4 vs IPv6​

IPv4

  • Uses 32-bit binary addresses
  • Expressed as four decimal numbers separated by dots (e.g., 192.168.1.1)
  • Each section is called an octet (8 bits)

IPv6

  • Uses 128-bit binary addresses
  • Expressed as eight groups of hexadecimal numbers separated by colons
  • Groups of zeros can be omitted to save space

Special IP Addresses​

  • 0.0.0.0 — Default network
  • 255.255.255.255 — Network broadcast
  • 127.0.0.1 — Loopback address (localhost)
  • 169.254.0.1 to 169.254.255.254 — Automatic Private IP Addressing (APIPA)

Essential Networking Commands​

Network Status​

# Show socket ports and states
netstat -a

# Protocol stats and error counts
netstat -s

# Routing table dump
netstat -r

# List interfaces
netstat -i

# Run continuously every N seconds
netstat <seconds>

# Numeric addresses (avoid DNS lookup)
netstat -n

# Modern replacement for netstat
ss -tuln  # Show all listening TCP/UDP ports

Network Interfaces​

# Show all interfaces
ifconfig -a

# Configure a specific interface
ifconfig <interface>

# Set interface parameters (root only)
ifconfig <interface> <params>

# Show filesystem mounts
df .

# Show NFS mounts
df -t nfs

Connectivity Testing​

# Test if host is reachable
ping <host>

# Trace route to destination
traceroute <host>

# More detailed version
traceroute -I <host>

# Test TCP connection to specific port
telnet <host> <port>

DNS & Name Resolution​

# Query DNS server
nslookup <host>

# Extended query
nslookup

# Print ARP table (IP to Ethernet mapping)
arp -a

File Transfer & Remote Access​

# FTP file transfer
ftp <host>

# Remote copy between systems
rcp <switches> system:file system:file

# Remote shell
rsh <host> <command>

# Remote login
rlogin <host> -l <login>

Process & System Monitoring​

# List processes
ps aux

# List processes (alternative format)
ps alx

# Your foreground processes
ps

# Filter processes by string
ps aux | grep <string>

Network Analysis​

# tcpdump — Packet sniffer
# Captures and interprets packets from network interface
tcpdump -i <interface>

# Save packets for analysis
tcpdump -w filename.pcap

# Display detailed packet info
tcpdump -v -i <interface>

Routing​

# Print routing tables
netstat -r

# Add/delete static routes
route add/del <destination>

# BSD dynamic routing daemon
routed

# Alternative routing daemon (OSPF, EGP, RIP)
gated

Important System Files​

FilePurpose
/etc/hostsMap hostnames to IP addresses
/etc/networksMap network names to IP addresses
/etc/protocolsMap protocol names to protocol numbers
/etc/servicesMap TCP/UDP service names to port numbers
/etc/fstabFilesystem mount points for boot time
/etc/exportsNFS export points
/etc/mtabCurrent mount table

Learning Path​

Start with fundamentals and progress through intermediate and advanced topics:

Beginner Path​

  1. Fundamentals — Master OSI/TCP-IP models, IP addressing, subnetting, DNS, DHCP, ARP
  2. Routing & Switching — Understand basic routing, VLANs, spanning tree
  3. Cheatsheet — Reference essential commands

Intermediate Path​

  1. Routing & Switching (Advanced) — Deep dive into OSPF, BGP, MPLS
  2. Security — Firewalls, IPsec, VPN, 802.1X

Advanced Path​

  1. Interview Questions — Scenario-based troubleshooting and design
  2. Security (Advanced) — Network attacks, defense strategies

Documentation​

Reference by Topic​

TopicLocation
OSI Model, IP addressing, SubnettingFundamentals
Routing protocols (OSPF, BGP, RIP, EIGRP, IS-IS)Routing & Switching
VLANs, Spanning Tree, NAT, MPLS, WANRouting & Switching
Firewalls, IPsec, VPN, 802.1X, ACLsSecurity
Network attacks and defense strategiesSecurity
100+ commands (netstat, tcpdump, dig, nmap)Cheatsheet
Protocol quick reference (TCP/IP, DNS, ICMP)Cheatsheet
40+ interview questions with answersInterview Q&A

Contributing​

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