What is Networking?

Overview

Build a production mental model of networking for Cloud and DevOps: what a network is, how network types differ, which topologies you will meet, and how to capture a baseline of your Linux host’s path to the Internet.

A network is a set of systems that exchange data. In Cloud and DevOps work that exchange is never abstract — it is the reason a pod reaches a database, a CI runner pulls an image, or a user hits your load balancer.

This course teaches networking from an operations and troubleshooting perspective, not as classic campus switching theory alone. Module 1 answers: what are we connecting, over which kind of network, and in which shape?

This is Module 1 — Networking Fundamentals of Networking for Cloud & DevOps Engineers.

This is a core tutorial in Module 1 · Networking Fundamentals of the REBASH Academy Networking for Cloud & DevOps Engineers series — written for Cloud, DevOps, Platform, and SRE engineers.

Prerequisites

Required

• Basic Linux knowledge and terminal familiarity
• A Linux lab host (Ubuntu 22.04/24.04, WSL2, or cloud free tier)

Recommended

• Linux Fundamentals

Learning Objectives

By the end of this tutorial, you will be able to:

• Define networking in operational terms (nodes, links, endpoints, paths)
• Compare LAN, MAN, WAN, Internet, Intranet, Extranet, and VPN
• Recognise common topologies (star, bus, mesh) and where they appear today
• Explain bandwidth, latency, and throughput with incident examples
• Map classic network types to cloud VPC and hybrid designs
• Capture a Linux network baseline with ip, ping, and traceroute

Architecture

Every Cloud / DevOps request travels a path of trust boundaries.

Theory

What is networking?

Networking is how nodes exchange data over links so applications can talk to endpoints.

Term	Meaning	Example
Node	Device that sends/receives	VM, laptop, router, pod
Link	Path between nodes	Ethernet, Wi‑Fi, VPN tunnel
Host	Node running workloads	EC2 instance, bare metal
Endpoint	Service address	10.0.1.5:5432, api.example.com:443
Path	Sequence of hops	Client → LB → app → DB

If you can name the path, you can troubleshoot the path.

Network types

Type	Scope	DevOps relevance
LAN	Building, rack, or logical cloud network	Office LAN; VPC ≈ logical LAN
MAN	City / metro	Less common day-to-day; ISP metro links
WAN	Distant sites / regions	Site-to-site VPN, Direct Connect / ExpressRoute
Internet	Public global network	Public APIs, registries, CDNs
Intranet	Private organisational network	Internal apps, private DNS
Extranet	Controlled partner access	Vendor VPN, private APIs for partners
VPN	Encrypted overlay across untrusted networks	Remote admin, hybrid cloud

Internet vs Intranet vs Extranet

	Internet	Intranet	Extranet
Audience	Anyone (public)	Employees / internal systems	Specific partners
Trust	Untrusted	Higher trust, still segmented	Contractual trust
Example	Public website	Internal wiki, CI	Supplier inventory API

VPN in one paragraph

A VPN creates an encrypted tunnel so private traffic can cross a public or untrusted network. In Cloud/DevOps you meet client VPNs (admin access) and site-to-site VPNs (datacentre ↔ VPC). Later modules cover WireGuard/IPsec patterns; here, treat VPN as “private connectivity over someone else’s network.”

Network topologies

Topology	Idea	Where you still see it
Star	Endpoints meet at a central switch	Most LANs, ToR switches
Bus	Shared backbone (historic)	Rare in modern Ethernet
Mesh	Many-to-many links	Spine-leaf fabrics, service meshes (logical), BGP at edge
Hybrid	Mix of the above	Almost every real enterprise / cloud design

Modern data centres prefer spine-leaf (a structured mesh). Cloud abstracts the cables; your job is still to design failure domains and paths.

Bandwidth, latency, throughput

Metric	Meaning	Unit
Bandwidth	Maximum rate a link can carry	Mbps / Gbps
Latency	Time for a packet to travel	ms
Throughput	Rate actually achieved	Mbps / Gbps

A wide pipe with high latency is fine for bulk sync and poor for chatty APIs. Design chatty tiers in the same AZ/region when you can.

Client-server (the default)

Production systems are usually client-server: clients initiate, servers listen, scale happens behind load balancers. Peer-to-peer appears in specialised systems (gossip, some storage), but your first mental model should be client-server.

Hands-on Lab

Focus: practise the core workflow for What is Networking?

mkdir -p ~/rebash-networking/module-01
cd ~/rebash-networking/module-01

sudo apt-get update
sudo apt-get install -y iproute2 iputils-ping traceroute curl

Step 1 — Confirm the lab host

cd ~/rebash-networking/module-01
uname -a
. /etc/os-release && echo "$PRETTY_NAME"

Step 2 — Identify your attachment to the network

ip -br link
ip -br addr

Expected: A primary interface UP with an IPv4 CIDR (LAN/VPC address).

Step 3 — Find the gateway (edge of your LAN)

ip route show default

Expected: default via <gateway> dev <iface> — your WAN/Internet exit from this LAN.

Step 4 — Classify your address

IP=$(ip -4 -o addr show scope global | awk '{print $4; exit}' | cut -d/ -f1)
echo "Address: $IP"
case "$IP" in
  10.*|192.168.*|172.1[6-9].*|172.2[0-9].*|172.3[0-1].*) echo "Likely private (Intranet / VPC style)" ;;
  *) echo "Public or other — treat as Internet-facing until proven otherwise" ;;
esac

Step 5 — Measure path characteristics

ping -c 5 1.1.1.1 || echo "ICMP filtered — try TCP next"
traceroute -n 1.1.1.1 | head -n 12 || true
curl -sI --max-time 10 https://example.com/ | head -n 5

Expected: Either ICMP RTT samples or a clear filter; traceroute hops; HTTP headers proving an application path works.

Step 6 — Write a fundamentals baseline

{
  echo "=== identity ==="
  hostnamectl 2>/dev/null || hostname
  echo
  echo "=== addresses ==="
  ip -br addr
  echo
  echo "=== default ==="
  ip route show default
  echo
  echo "=== notes ==="
  echo "network_type_guess: private LAN/VPC or public — fill from Step 4"
  echo "topology_guess: star (typical access LAN) unless told otherwise"
} | tee fundamentals-baseline.txt

Validation

• You can define node, link, endpoint, and path
• You can contrast LAN, WAN, Internet, Intranet, Extranet, and VPN
• You can name star vs mesh with one modern example each
• fundamentals-baseline.txt exists
• You reached an HTTPS endpoint from the lab host

test -f ~/rebash-networking/module-01/fundamentals-baseline.txt && echo "baseline: OK"

Code Walkthrough

Production practice for What is Networking? always combines:

1. Inspect before you change (status, plan, logs, dry-run)
2. Prefer reversible, documented changes (Git, IaC, drop-ins, version pins)
3. Capture evidence (command output, pipeline logs) for handovers
4. Prefer current tools and APIs over legacy shortcuts
5. Least privilege — escalate credentials only when required

Keep runbooks short enough to follow under pressure. Automate checks; keep humans for judgement.

Security Considerations

• Treat credentials and tokens for networking as privileged — never commit them
• Prefer short-lived auth (OIDC, roles, SSO) over long-lived keys
• Validate blast radius before apply/deploy/delete operations
• Restrict who can approve production changes
• Collect audit logs; limit who can read sensitive traces

Common Mistakes

Skipping fundamentals for What is Networking?

Validate assumptions against the Theory section and official docs before changing production.

Treating lab defaults as production-ready for What is Networking?

Lab shortcuts (open security groups, admin roles, skip approvals) must not ship unchanged.

Changing production without a rollback path

Always know how to revert (previous artefact, prior release, state rollback, DNS failback).

Best Practices

• Encode What is Networking? changes as code and review them in pull requests
• Pin versions (images, modules, actions, provider plugins)
• Separate environments with clear promotion gates
• Alert on symptoms with runbooks attached
• Destroy lab resources; tag everything with owner and expiry where possible

Troubleshooting

Symptom	Likely meaning	Next check
No default route	Not attached to a gateway / DHCP failed	ip route, cloud route table
Private IP but no Internet	Missing NAT / VPN / proxy	Egress path design
Ping fails, HTTPS works	ICMP filtered	Trust application port tests
High latency	Distant region / long WAN path	Prefer local AZ

Summary

• Networking is how nodes exchange data along paths to endpoints.
• LAN / MAN / WAN / Internet / Intranet / Extranet / VPN describe scope and trust.
• Topologies (star, mesh, hybrid) still matter as failure-domain thinking.
• Measure bandwidth, latency, and throughput separately.
• Capture a Linux baseline before you need it in an incident.

Interview Questions

1. How does What is Networking? show up when operating Cloud or production platforms?
2. What would you check first if this area misbehaves in production?
3. Which modern tools or APIs replace older equivalents here?
4. What security control should accompany this capability?
5. How would you automate verification of this topic in CI?

Sample answer — question 2

Start with blast radius and recent changes, gather evidence (logs, status, plan/diff), then fix forward with a known rollback path — not guesswork.

Related Tutorials

• Course overview
• • Continue with OSI Model — the seven-layer vocabulary you will use in every incident.

References

• RFC 1122 – Requirements for Internet Hosts
• NIST SP 800-47 – Security Guide for Interconnecting IT Systems
• AWS VPC overview