Key Decision Factors
LAN vs WAN
LAN = Same site, owned by you
WAN = Multiple sites, uses external links
Client-Server vs P2P
C-S = Large, managed, secure
P2P = Small, simple, cheap
Star vs Mesh
Star = Easy, central point of failure
Mesh = Reliable, expensive
Hardware Choice
Switch = Within LAN
Router = Between networks
Designing a School Network
Scenario
A school is setting up a new computer network with 100 computers across 5 classrooms. They need:
- Students to access shared files and printers
- Central user account management
- Regular backups of student work
- Easy expansion for future classrooms
Design the network type, model, and topology.
Solution
Determine network type (LAN or WAN)
All 5 classrooms are in one school building
Single site, owned by the school
Answer: LAN
Determine network model (Client-Server or P2P)
100 computers - too many for P2P
Need centralised accounts, files, and backups
School has IT staff to manage servers
Answer: Client-Server
Determine topology (Star or Mesh)
Need easy expansion for new classrooms
Cost is a factor (not critical infrastructure)
Star is simpler to manage and expand
Answer: Star topology
List required hardware
- File server - stores student work
- Switches - one per classroom to connect computers
- Central switch - connects classroom switches together
- Router - connects LAN to internet
- WAPs - if wireless access needed
- NICs - in every computer
Complete Design
Type: LAN (single site)
Model: Client-Server (centralised management)
Topology: Star (easy expansion)
Hardware: File server, switches, router, WAPs, NICs
Diagnosing Network Issues
Scenario
A user reports that their computer cannot access the internet, but they can access shared files on the office server. Other computers work fine.
Identify the likely cause and solution.
Solution
Analyse what works and what doesn't
- CAN access server = computer IS connected to LAN
- CANNOT access internet = problem is external connection
- Other computers work = router and internet are fine
Narrow down the issue
The NIC is working (LAN access works)
The switch is working (LAN access works)
The router is working (others have internet)
Problem must be this computer's network settings
Identify likely causes
- Wrong gateway address - computer doesn't know where router is
- DNS settings incorrect - can't resolve website names
- Proxy settings wrong - browser misconfigured
- Firewall blocking - software blocking internet
Answer
Likely cause: Incorrect network configuration (gateway/DNS settings) on this specific computer
Solution:
- Check IP configuration (gateway address)
- Verify DNS server settings
- Try setting to "Obtain automatically" (DHCP)
- Check firewall/proxy settings
Cloud vs Local Storage Decision
Scenario
A small business is deciding where to store their files. They have:
- 10 employees who sometimes work from home
- Limited IT budget and no IT staff
- Need to collaborate on documents
- Reliable internet connection
Should they use cloud storage or local file server?
Solution
Evaluate cloud storage for this scenario
Advantages that apply:
- Access from home - employees can work remotely
- No server hardware to buy/maintain
- No IT staff needed - provider handles everything
- Built-in collaboration tools
- Automatic backups included
Evaluate local file server
Disadvantages for this scenario:
- Expensive server hardware needed
- IT expertise required for setup and maintenance
- Remote access is complicated to configure
- Backups are their responsibility
- Collaboration features would need extra software
Consider potential cloud disadvantages
- Internet required - but they have reliable internet
- Ongoing subscription - but cheaper than server + IT staff
- Data on third-party servers - acceptable for most business files
Recommendation: Cloud Storage
Best choice for this business because:
- Supports remote working (key requirement)
- No upfront hardware costs
- No IT expertise needed
- Collaboration built-in
- Provider handles backups and security
Suggested services: Microsoft 365, Google Workspace, or Dropbox Business
Choosing the Right Hardware
Scenario
A home user wants to:
- Connect 3 computers to share a printer
- Connect all devices to the internet
- Use WiFi for laptops and phones
What hardware do they need?
Solution
Identify the requirements
- Connect devices together (LAN) = needs switch
- Connect to internet = needs router
- Provide WiFi = needs wireless access point
Consider practical solutions
Buying 3 separate devices would be expensive
Home routers typically combine all three functions:
- Router (connects to internet)
- Switch (built-in ports for wired devices)
- Wireless access point (WiFi antenna)
Check device capabilities
Each computer needs a NIC:
- Desktop computers - usually have built-in Ethernet NIC
- Laptops - have both Ethernet and WiFi NICs
- Phones/tablets - have WiFi NIC only
Shopping List
- Home wireless router (combines router + switch + WAP)
- Ethernet cables for desktop computers
- NICs - likely already built into all devices
Most ISPs provide a combined router when you sign up for internet service!
Choosing Network Topology
Scenario
A data centre needs to connect 4 critical database servers. The requirements are:
- Maximum reliability - data must always be accessible
- No single point of failure acceptable
- Budget is not a primary concern
Which topology should they use?
Solution
Evaluate Star Topology
For this scenario:
- Central switch = single point of failure
- If switch fails, all servers lose connection
- Does NOT meet the reliability requirement
Verdict: Not suitable
Evaluate Mesh Topology
For this scenario:
- Every server connected to every other server
- Multiple paths for data
- If one connection fails, use another route
- No single point of failure
Verdict: Meets all requirements
Consider the trade-offs
Mesh disadvantages:
- More expensive - but budget isn't a concern
- Complex setup - acceptable for data centre
- Each server needs multiple NICs - 4 servers is manageable
Answer: Full Mesh Topology
Why:
- No single point of failure
- Maximum reliability through redundant paths
- Only 4 servers, so manageable complexity
- Worth the extra cost for critical data
Connections needed: 6 (each server connects to 3 others)
How DNS Works
Scenario
A user types "www.bbc.co.uk" into their browser.
Explain the step-by-step process of how DNS helps load the website.
Solution
Browser checks local cache
Computer first checks if it recently looked up this address
If found in cache, skip to step 5
If not found, continue to DNS lookup
Query sent to DNS server
Computer sends request to its configured DNS server
(Usually provided by your ISP or set to Google/Cloudflare)
"What is the IP address for www.bbc.co.uk?"
DNS server looks up the address
DNS server checks its records
May query other DNS servers hierarchically if not found
Finds: www.bbc.co.uk = 151.101.0.81
IP address returned to computer
DNS server sends back: "151.101.0.81"
Computer caches this for future use
Browser connects to web server
Browser sends HTTP request to 151.101.0.81
BBC's web server receives the request
Server sends back the web page
Browser displays the page
Summary
DNS purpose: Translates human-readable domain names into IP addresses that computers use to communicate.
Why important: Without DNS, users would need to memorise IP addresses like 151.101.0.81 instead of easy names like www.bbc.co.uk
Practice Problems
Try these on your own, then reveal the answers to check.
Practice 1: LAN or WAN?
A company has offices in London and Manchester. Each office has its own internal network, and the two offices are connected to share data.
WAN - The connection between London and Manchester is a WAN (wide area network). Each office has a LAN, and the WAN connects these two LANs together.
Practice 2: Star or Mesh?
A school is setting up a computer lab with 30 student computers. They want a simple, affordable network that's easy to manage.
Star topology - Simple to set up, easy to add/remove computers, affordable (just need a switch), and easy to troubleshoot. Mesh would be unnecessarily expensive and complex for a school lab.
Practice 3: Hardware Needed
A company's LAN can access internal servers but cannot reach any websites. What hardware might be faulty or missing?
Router - The switch is working (LAN access works), but the router that connects the LAN to the internet is either faulty, misconfigured, or missing. The DNS server could also be the issue if websites don't resolve.