A practical networking reference guide covering core concepts, protocols, configurations, and troubleshooting — by Frank Armah, HCIA Datacom Certified (Huawei Technologies).
This repo documents my networking knowledge from academic study, hands-on experience at the Electricity Company of Ghana (ECG), and my Huawei HCIA Datacom certification. It covers:
- ✅ Core networking concepts and the OSI model
- ✅ IP addressing and subnetting
- ✅ Key protocols explained simply
- ✅ Network devices and their roles
- ✅ Routing and switching fundamentals
- ✅ Troubleshooting techniques
- ✅ Real-world scenarios from IT practice
| Certificate | Issuer |
|---|---|
| 🏅 HCIA Datacom — Huawei Certified ICT Associate (Data Communications) | Huawei Technologies |
- The OSI Model
- TCP/IP Model
- IP Addressing & Subnetting
- Key Networking Protocols
- Network Devices
- Routing Fundamentals
- Switching Fundamentals
- Wireless Networking
- Troubleshooting
- Real-World Scenarios
- Quick Reference Commands
- Resources
The Open Systems Interconnection (OSI) model is the foundation of networking — it describes how data travels from one device to another across a network.
| Layer | Name | Function | Example Protocols/Devices |
|---|---|---|---|
| 7 | Application | Interface for end-user applications | HTTP, HTTPS, FTP, DNS, SMTP |
| 6 | Presentation | Data formatting, encryption, compression | SSL/TLS, JPEG, MP4 |
| 5 | Session | Manages sessions between applications | NetBIOS, RPC |
| 4 | Transport | End-to-end delivery, error checking | TCP, UDP |
| 3 | Network | Logical addressing and routing | IP, ICMP, Routers |
| 2 | Data Link | Physical addressing (MAC), framing | Ethernet, Switches, MAC |
| 1 | Physical | Raw bit transmission over media | Cables, Hubs, Wi-Fi signals |
💡 Memory tip: "All People Seem To Need Data Processing" (Layer 7 to 1)
The practical model used in real-world internet communications:
| TCP/IP Layer | Corresponds to OSI Layers | Protocols |
|---|---|---|
| Application | 5, 6, 7 | HTTP, DNS, SMTP, FTP |
| Transport | 4 | TCP, UDP |
| Internet | 3 | IP, ICMP, ARP |
| Network Access | 1, 2 | Ethernet, Wi-Fi |
| Feature | TCP | UDP |
|---|---|---|
| Connection | Connection-oriented | Connectionless |
| Reliability | Guaranteed delivery | No guarantee |
| Speed | Slower | Faster |
| Use case | Web browsing, email, file transfer | Streaming, gaming, VoIP |
| Class | Range | Default Subnet Mask | Use |
|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | 255.0.0.0 /8 | Large networks |
| B | 128.0.0.0 – 191.255.255.255 | 255.255.0.0 /16 | Medium networks |
| C | 192.0.0.0 – 223.255.255.255 | 255.255.255.0 /24 | Small networks |
| Range | Class |
|---|---|
| 10.0.0.0 – 10.255.255.255 | A |
| 172.16.0.0 – 172.31.255.255 | B |
| 192.168.0.0 – 192.168.255.255 | C |
Subnetting divides a large network into smaller, manageable sub-networks.
Example:
Network: 192.168.1.0/24
Subnet Mask: 255.255.255.0
Total Hosts: 254 usable hosts
Subnet into /26 (4 subnets):
Subnet 1: 192.168.1.0 – 192.168.1.63 (62 hosts)
Subnet 2: 192.168.1.64 – 192.168.1.127 (62 hosts)
Subnet 3: 192.168.1.128 – 192.168.1.191 (62 hosts)
Subnet 4: 192.168.1.192 – 192.168.1.255 (62 hosts)
- 128-bit address (vs 32-bit IPv4)
- Written in hexadecimal:
2001:0db8:85a3:0000:0000:8a2e:0370:7334 - Virtually unlimited addresses
- Built-in security (IPSec)
| Protocol | Port | Layer | Purpose |
|---|---|---|---|
| HTTP | 80 | Application | Web browsing (unencrypted) |
| HTTPS | 443 | Application | Secure web browsing |
| FTP | 21 | Application | File transfer |
| SFTP | 22 | Application | Secure file transfer |
| SSH | 22 | Application | Secure remote access |
| Telnet | 23 | Application | Remote access (insecure) |
| DNS | 53 | Application | Domain name to IP resolution |
| DHCP | 67/68 | Application | Automatic IP assignment |
| SMTP | 25 | Application | Sending email |
| SNMP | 161 | Application | Network device monitoring |
| ICMP | — | Network | Ping, error messages |
| ARP | — | Data Link | IP to MAC address resolution |
- Operates at Layer 1 (Physical)
- Broadcasts data to all connected devices
⚠️ Outdated — causes collisions and security issues- Replaced by switches
- Operates at Layer 2 (Data Link)
- Uses MAC addresses to send data only to the intended device
- Creates separate collision domains
- More efficient and secure than hubs
- Operates at Layer 3 (Network)
- Connects different networks together
- Uses IP addresses to forward packets
- Makes routing decisions based on routing tables
- Provides wireless connectivity to a wired network
- Extends LAN wirelessly
- Uses Wi-Fi standards (802.11a/b/g/n/ac/ax)
- Monitors and filters incoming/outgoing network traffic
- Enforces security policies
- Can be hardware or software based
- Converts digital signals to analogue and back
- Connects local network to the internet via ISP
| Feature | Static Routing | Dynamic Routing |
|---|---|---|
| Configuration | Manual | Automatic |
| Adaptability | Does not adapt to changes | Adapts to network changes |
| Best for | Small, simple networks | Large, complex networks |
| Protocols | None | OSPF, RIP, EIGRP, BGP |
| Protocol | Type | Use Case |
|---|---|---|
| RIP | Distance Vector | Small networks, simple setups |
| OSPF | Link State | Large enterprise networks |
| EIGRP | Hybrid | Cisco networks |
| BGP | Path Vector | Internet routing between ISPs |
Logically segments a network without needing separate physical infrastructure.
Benefits:
- Improved security (isolates departments)
- Reduced broadcast traffic
- Better network management
Example:
VLAN 10 → IT Department
VLAN 20 → Finance Department
VLAN 30 → Operations Department
Prevents network loops in switched networks by blocking redundant paths.
Switches learn and store MAC addresses to know which port to send data to.
| Standard | Frequency | Max Speed | Range |
|---|---|---|---|
| 802.11b | 2.4 GHz | 11 Mbps | Medium |
| 802.11g | 2.4 GHz | 54 Mbps | Medium |
| 802.11n | 2.4/5 GHz | 600 Mbps | Good |
| 802.11ac | 5 GHz | 3.5 Gbps | Good |
| 802.11ax (Wi-Fi 6) | 2.4/5/6 GHz | 9.6 Gbps | Excellent |
| Protocol | Security Level | Notes |
|---|---|---|
| WEP | ❌ Very Weak | Outdated — never use |
| WPA | Avoid if possible | |
| WPA2 | ✅ Strong | Current standard |
| WPA3 | ✅✅ Strongest | Latest — use when available |
Step 1 → IDENTIFY the problem
"What is not working? Since when?"
Step 2 → ESTABLISH a theory
"What could be causing this?"
Step 3 → TEST the theory
"Ping, traceroute, check cables/connections"
Step 4 → IMPLEMENT the fix
"Apply the solution"
Step 5 → VERIFY
"Confirm the issue is resolved"
Step 6 → DOCUMENT
"Record what happened and how it was fixed"
# Test connectivity
ping 8.8.8.8
# Trace the route packets take
traceroute google.com # Linux/Mac
tracert google.com # Windows
# Check IP configuration
ipconfig # Windows
ifconfig # Linux/Mac
ip addr # Linux
# DNS lookup
nslookup google.com
dig google.com
# Check open ports and connections
netstat -an
# Scan network for devices
nmap -sn 192.168.1.0/24
# Check ARP table
arp -a
# Release and renew IP (Windows)
ipconfig /release
ipconfig /renew
# Flush DNS cache
ipconfig /flushdns # Windows
sudo systemd-resolve --flush-caches # Linux| Problem | Possible Cause | Solution |
|---|---|---|
| No internet connection | IP conflict, DNS issue, cable | Check IP, flush DNS, reseat cable |
| Slow network | Bandwidth congestion, interference | QoS, change Wi-Fi channel |
| Cannot reach specific site | DNS failure | Change DNS to 8.8.8.8 |
| IP conflict | Two devices same IP | Check DHCP, assign static IP |
| Packet loss | Cable issue, overloaded link | Test cable, check utilisation |
| Wi-Fi drops frequently | Interference, weak signal | Change channel, move AP |
Situation: Staff at an ECG branch office cannot access the central system.
Troubleshooting steps:
- Ping the branch router from central — no response
- Check physical connections at the branch
- Check if the router has power and is operational
- Verify WAN link status on the router
- Check routing table for correct routes
- Contact ISP if WAN link is down
Resolution: WAN cable had come loose — reseated cable restored connectivity.
Situation: Network becomes very slow between 9am–12pm when all staff are working.
Investigation:
- Monitor bandwidth utilisation — shows 95%+ usage
- Identify top bandwidth consumers using network monitoring tool
- Discover large file downloads consuming bandwidth
Resolution: Implemented Quality of Service (QoS) to prioritise business-critical traffic over downloads.
Situation: A new workstation cannot connect to the network — showing "Limited Connectivity".
Troubleshooting:
- Check if DHCP server is reachable
- Run
ipconfig /releasethenipconfig /renew - Check DHCP server has available IP addresses in pool
- Check VLAN assignment on the switch port
Resolution: DHCP pool was exhausted — expanded the IP range on the DHCP server.
# Enter system view
system-view
# Display device info
display version
# Display interface status
display interface brief
# Display routing table
display ip routing-table
# Configure IP on interface
interface GigabitEthernet0/0/0
ip address 192.168.1.1 255.255.255.0
# Save configuration
save- Huawei Learning — HCIA Datacom study materials
- Cisco Networking Academy — Free networking courses
- Professor Messer — CompTIA Network+ study guide
- Subnet Calculator — Subnetting tool
- Wireshark — Network packet analyser
- GNS3 — Network simulation software
⭐ If you find this useful, feel free to star the repo!
— Frank Armah | IT Professional | Ghana 🇬🇭