Networking is one of the most important skills for IT Support, Windows Administration, Cloud and DevOps. You should understand how a computer gets an IP address, communicates with other devices, accesses websites, and connects to the Internet.
1. What is Computer Networking?
Networking means connecting computers and devices so they can communicate and share resources.
Simple example
When you open:
https://www.google.com
Your computer roughly does this:
Your PC ↓ Private IP ↓ Default Gateway / Router ↓ DNS → Finds Google's IP ↓ Internet ↓ Google Server
Common network devices
|
Device |
Main Job |
|
PC/Laptop |
End device |
|
Switch |
Connects devices inside a LAN |
|
Router |
Connects different networks |
|
Modem/ONT |
Connects your network to ISP |
|
Access Point |
Provides Wi-Fi |
|
Firewall |
Controls network traffic |
|
Server |
Provides services/resources |
2. IP Address
An IP address identifies a device on a network.
Example:
192.168.1.10
Think of an IP address like a house address.
If Computer A wants to communicate with Computer B, it needs to know where Computer B is located on the network.
Example
PC-1 → 192.168.1.10 PC-2 → 192.168.1.20 Printer → 192.168.1.50 Router → 192.168.1.1→ 192.168.4.2
Mobile
3. Public IP Address
A Public IP is an address used to communicate over the Internet.
Your ISP normally provides a public IP to your router/network.
Example:
Internet ↓ Public IP 203.x.x.x ↓ Home Router ↓ Private Network ↓ PC / Mobile / TV
Important
A public IP can generally be reachable from the Internet, subject to routing, NAT and firewall rules.
4. Private IP Address
Private IP addresses are used inside local networks.
The main IPv4 private ranges are:
| Range | CIDR |
|---|---|
10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 |
172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 |
192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 |
Example:
Laptop → 192.168.1.10 Mobile → 192.168.1.11 Printer → 192.168.1.20 Router → 192.168.1.1
Private IPs are not directly routable on the public Internet. Home and office routers commonly use NAT to allow private devices to access the Internet.
5. IPv4
IPv4 uses 32 bits.
Example:
192.168.1.10
It contains four numbers called octets.
192 . 168 . 1 . 10
Each octet can range from:
0 – 255
Example
IP Address: 192.168.1.10 Subnet: 255.255.255.0 Gateway: 192.168.1.1 DNS: 8.8.8.8
6. IPv6 Basics
IPv6 was created because IPv4 has a limited number of addresses.
IPv6 uses 128 bits.
Example:
2001:db8:1234:5678::1
IPv6 uses hexadecimal numbers separated by :.
IPv4 vs IPv6
|
Feature |
IPv4 |
IPv6 |
|
Address size |
32-bit |
128-bit |
|
Example |
192.168.1.10 |
2001:db8::1 |
|
Address availability |
Limited |
Extremely large |
|
Notation |
Decimal |
Hexadecimal |
|
Broadcast |
Supported |
No traditional broadcast |
Easy way to remember
IPv4 = 32-bit IPv6 = 128-bit
7. Subnet Mask
A subnet mask tells your computer which part of an IPv4 address represents the network and which part represents the host.
Example:
IP Address: 192.168.1.10 Subnet Mask: 255.255.255.0
This is commonly written as:
192.168.1.10/24
Simple understanding
192.168.1 = Network 10 = Host
For a typical /24 network:
Network: 192.168.1.0 Usable: 192.168.1.1 – 192.168.1.254 Broadcast: 192.168.1.255
8. CIDR
CIDR = Classless Inter-Domain Routing
CIDR represents the network prefix using /number.
Examples:
| CIDR | Common subnet mask |
|---|---|
/8 | 255.0.0.0 |
/16 | 255.255.0.0 |
/24 | 255.255.255.0 |
/25 | 255.255.255.128 |
/26 | 255.255.255.192 |
/27 | 255.255.255.224 |
/28 | 255.255.255.240 |
/30 | 255.255.255.252 |
Important concept
For IPv4:
/24 → 256 total addresses → normally 254 usable host addresses
The network and broadcast addresses are not normally assigned to hosts.
9. Default Gateway
The Default Gateway is normally your router's IP address.
It allows your computer to communicate with other networks.
Example:
PC 192.168.1.10 ↓ Gateway 192.168.1.1 ↓ Internet
If your gateway is incorrect or unavailable:
Local network → May work Internet → Usually fails
Check gateway
ipconfig
Look for:
Default Gateway . . . : 192.168.1.1
10. DNS
DNS = Domain Name System
DNS converts human-readable domain names into IP addresses.
Instead of remembering:
142.x.x.x
you type:
google.com
DNS finds the corresponding IP address.
Simple example
You type: google.com ↓ DNS ↓ IP Address ↓ Google Server
Common DNS servers
Google DNS: 8.8.8.8 8.8.4.4 Cloudflare DNS: 1.1.1.1 1.0.0.1
11. DHCP
DHCP = Dynamic Host Configuration Protocol
DHCP automatically provides network configuration to devices.
It can provide:
IP Address Subnet Mask Default Gateway DNS Server
DHCP process
Remember:
DORA
D → Discover O → Offer R → Request A → Acknowledgement
Example:
Laptop joins Wi-Fi ↓ DHCP Server ↓ 192.168.1.25 255.255.255.0 192.168.1.1 8.8.8.8
12. MAC Address/Physical Address
MAC = Media Access Control Address
A MAC address identifies a network interface at the data-link layer.
Example:
A4-B1-C1-22-33-44
or
A4:B1:C1:22:33:44
IP vs MAC
|
IP Address |
Physical MAC Address |
|
Network-layer address |
Data-link-layer address |
|
Used for logical networking |
Used for local network communication |
|
Can change |
Usually associated with network hardware/interface |
|
Example 192.168.1.10 |
A4-B1-C1-22-33-44 |
Check MAC address:
ipconfig /all
or:
getmac
PowerShell:
Get-NetAdapter
13. TCP and UDP
TCP and UDP are transport-layer protocols.
TCP
TCP is connection-oriented and provides reliable, ordered delivery.
Used by many applications where reliable delivery matters.
Examples:
HTTPS SSH FTP
Think:
TCP = Reliable
UDP
UDP is connectionless and has less overhead.
It is useful when speed and low latency are important.
Examples include:
DNS DHCP VoIP Streaming Online gaming
Think:
UDP = Fast / lightweight
TCP vs UDP
|
TCP |
UDP |
|
Connection-oriented |
Connectionless |
|
Reliable delivery |
No delivery guarantee |
|
Ordered data |
No guaranteed ordering |
|
More overhead |
Less overhead |
|
Example HTTPS |
Example DNS |
14. Ports
A port number identifies a service/application endpoint on a device.
Think of:
IP = Building address Port = Door number
Important ports
|
Port |
Protocol/Service |
Common use |
|
20/21 |
FTP |
File transfer |
|
22 |
SSH |
Secure remote access |
|
23 |
Telnet |
Remote access, insecure |
|
25 |
SMTP |
Email transfer |
|
53 |
DNS |
Name resolution |
|
67/68 |
DHCP |
IP configuration |
|
80 |
HTTP |
Web |
|
110 |
POP3 |
Email |
|
123 |
NTP |
Time synchronization |
|
143 |
IMAP |
Email |
|
443 |
HTTPS |
Secure web |
|
3389 |
RDP |
Windows Remote Desktop |
Example
192.168.1.10:443
Means:
IP Address = 192.168.1.10 Port = 443 Service = HTTPS
15. VPN
VPN = Virtual Private Network
A VPN creates an encrypted connection between your device/network and a VPN endpoint.
Example:
Laptop ↓ Encrypted VPN Tunnel ↓ VPN Server ↓ Internet / Company Network
Common uses-
- Secure remote access
- Connecting to company networks
- Protecting traffic on untrusted networks
- Site-to-site connectivity
Important
A VPN does not automatically make you completely anonymous or secure from every threat. Security depends on the VPN technology, provider, configuration and endpoint security.
16. Firewall
A firewall controls network traffic according to security rules.
It can allow or block:
IP addresses Ports Protocols Applications Network profiles
Example:
Internet ↓ Firewall ↓ Allow TCP 443 ↓ Web Server
If a firewall blocks TCP 443, HTTPS connectivity can fail.
Windows Firewall-
Open:
wf.msc
or:
Windows Security → Firewall & network protection
17. Important Networking Commands
Windows CMD
1. ipconfig
Shows basic IP configuration.
ipconfig
More details
ipconfig /all
Useful for checking:
- IPv4
- IPv6
- Subnet mask
- Default gateway
- DNS
- DHCP
- MAC/physical address
2. Release IP
ipconfig /release
Get a new IP
ipconfig /renew
Useful when DHCP configuration is problematic.
3. Clear DNS cache
ipconfig /flushdns
Useful when troubleshooting DNS-related problems.
18. ping
Tests basic network reachability.
ping 8.8.8.8
Test a domain:
ping google.com
Example
Reply from 8.8.8.8
means the destination responded to the ICMP echo request.
Important: A failed ping does not always mean the destination is down; firewalls may block ICMP.
19. tracert
Shows the path toward a destination.
tracert google.com
Example concept:
Your PC ↓ Router ↓ ISP ↓ Internet routers ↓ Destination
Useful when investigating where connectivity appears to stop or slow.
20. nslookup
Used to troubleshoot DNS.
nslookup google.com
Example:
Name: google.com Address: xxx.xxx.xxx.xxx
You can also query a specific DNS server:
nslookup google.com 8.8.8.8
21. arp
Displays the local ARP cache.
arp -a
ARP helps IPv4 devices discover the MAC/ Physical address associated with an IP address on the local network.
22. route
Displays the routing table.
route print
Useful for understanding where Windows sends network traffic.
23. netstat
Shows network connections and listening ports.
netstat -ano
Useful for checking:
- Active connections
- Listening ports
- Remote addresses
- Process IDs
Example:
TCP 0.0.0.0:443 LISTENING
24. Test-NetConnection – PowerShell
One of the most useful Windows networking troubleshooting commands.
Test-NetConnection google.com
Test a specific port:
Test-NetConnection google.com -Port 443
Example:
TcpTestSucceeded : True
This is especially useful when you need to determine whether a particular TCP port is reachable.
25. Useful PowerShell Networking Commands
|
Command |
Purpose |
|
Get-NetAdapter |
Network adapters |
|
Get-NetIPConfiguration |
IP configuration |
|
Get-NetIPAddress |
IP addresses |
|
Get-NetRoute |
Routing table |
|
Get-DnsClientServerAddress |
DNS servers |
|
Get-NetTCPConnection |
TCP connections |
|
Test-NetConnection |
Connectivity/port testing |
|
Resolve-DnsName google.com |
DNS lookup |
26. Practical Troubleshooting Flow
Suppose the user says:
"My computer has no Internet."
Don't immediately restart everything.
Follow this sequence:
1. Check Wi-Fi/Ethernet connection ↓ 2. Check network adapter ↓ 3. ipconfig ↓ 4. Check IP address ↓ 5. Check Default Gateway ↓ 6. Ping Gateway ↓ 7. Ping Internet IP ↓ 8. Test DNS ↓ 9. Check firewall/VPN ↓ 10. Fix and verify
Commands
ipconfig /all
Then:
ping <default-gateway>
For example:
ping 192.168.1.1
Then:
ping 8.8.8.8
Then:
nslookup google.com
27. Understand the Results
|
|---|
Important
169.254.x.x is an APIPA/link-local IPv4 address that Windows can assign when it cannot obtain a normal IPv4 configuration through DHCP.
28. OSI Model – Basic Networking Knowledge
For an IT Support Engineer, understand the OSI 7 layers.
|
Layer |
Name |
Example |
|
7 |
Application |
HTTP, DNS, SMTP |
|
6 |
Presentation |
Encoding, encryption concepts |
|
5 |
Session |
Session management |
|
4 |
Transport |
TCP, UDP, Ports |
|
3 |
Network |
IP, Routing |
|
2 |
Data Link |
MAC/Physical, Ethernet, Switches |
|
1 |
Physical |
Cable, Wi-Fi radio, fiber |
29. Important Networking Terms
|
Term |
Simple Meaning |
|
LAN |
Local Area Network |
|
WAN |
Wide Area Network |
|
WLAN |
Wireless LAN |
|
ISP |
Internet Service Provider |
|
NIC |
Network Interface Card |
|
NAT |
Translates private/public addressing |
|
DHCP |
Automatically gives network configuration |
|
DNS |
Converts names to IP addresses |
|
IP |
Logical network address |
|
MAC |
Interface/hardware address |
|
Router |
Connects networks |
|
Switch |
Connects devices on a LAN |
|
Firewall |
Controls network traffic |
|
VPN |
Encrypted network tunnel |
|
Port |
Identifies a service endpoint |
30. Practical Lab for You ⛤⭐☆
Lab 1 – Find your network configuration
ipconfig /all
Identify:
IPv4 Address Subnet Mask Default Gateway DNS Server MAC Address DHCP Enabled
Lab 2 – Test your router
ping <your-gateway-IP>
ping fe80::1%4
Lab 3 – Test Internet
ping 8.8.8.8
Lab 4 – Test DNS
nslookup google.com
Lab 5 – Trace the route
tracert google.com
Lab 6 – Check connections
netstat -ano
Lab 7 – Test HTTPS
Open PowerShell:
Test-NetConnection google.com -Port 443
Lab 8 – Check network adapter
Get-NetAdapter
Lab 9 – Check IP configuration
Get-NetIPConfiguration
Lab 10 – Check routes
Get-NetRoute
IT Support Engineer – Networking Checklist
You should be comfortable with these:
☑ IP Address ☑ Public vs Private IP ☑ IPv4 ☑ IPv6 basics ☑ Subnet Mask ☑ CIDR ☑ Default Gateway ☑ DNS ☑ DHCP ☑ MAC Address ☑ TCP / UDP ☑ Ports ☑ VPN ☑ Firewall ☑ NAT ☑ LAN / WAN ☑ Router / Switch ☑ OSI Model ☑ ipconfig ☑ ping ☑ tracert ☑ nslookup ☑ arp ☑ route ☑ netstat ☑ Test-NetConnection ☑ PowerShell networking commands
Most Important Troubleshooting Sequence
For interviews and real IT Support work, remember:
IP → Gateway → Internet → DNS → Port → Firewall → Application
For example:
Can I reach my Gateway? ↓ Can I reach the Internet? ↓ Can DNS resolve the name? ↓ Is the required port open? ↓ Is Firewall/VPN blocking it? ↓ Is the application itself working?
