📡 Application Layer Services

DHCP · DNS · HTTP · Email (SMTP/POP3) · Full User Experience

🌐 192.168.100.0/24 · 2 Servers · 4 Switches · 4 PCs

Network Topology – Servers & End Devices

🔍 Click image to zoom
Network topology diagram for Application Layer Services

📄 Packet Tracer File (Complete Application Layer Lab)

DHCP · DNS · HTTP · Email (SMTP/POP3) · 2 Servers · 4 PCs

⬇ Download App_Layer_Lab.pkt
Network
192.168.100.0/24
DHCP Pool
.50 – .59
DNS Record
www.puc.com → .20
Email Users
user1 / user2

👩‍💻 User Experience – What a User Actually Does

Imagine you are sitting at PC1 in the computer lab. You don’t need to know anything about IP addresses, subnet masks, or server configurations. The moment you turn on your computer, the DHCP server (192.168.100.10) automatically gives your PC an IP address like 192.168.100.51. You see the network icon show "Connected" — no manual setup required.

To browse the internal website, you open your web browser, type www.puc.com in the address bar, and press Enter. Behind the scenes, the DNS server translates that friendly name into the actual IP address 192.168.100.20 (HTTP server). Instantly, a welcome page appears: "Welcome to PUC Network – Application Layer Services Lab". You can click, refresh, or even navigate to test.html — it feels exactly like browsing the real internet, but everything stays inside your local network.

Now for email: You open the Email client on your desktop. You click Compose, type user2@puc.com in the "To" field, write a quick message like "Hello from PC1!", and hit Send. Your friend at PC2 opens their email client, clicks Receive, and sees your message instantly. They can reply, and when you click Receive again, you get their reply. No complicated settings — just like Gmail or Outlook. The SMTP and POP3 services on the same server handle the delivery. This lab perfectly mirrors how real-world networks provide DHCP, DNS, web, and email services, making everything seamless for the end user.

✨ Key takeaway: Users only care about typing a web address or sending an email — all the magic of application-layer protocols happens automatically thanks to correct server configurations.

📝 Step-by-Step Implementation

1Set Up the Topology
  • Open Cisco Packet Tracer
  • Add devices to workspace:
    • Click bottom toolbar → End Devices → Drag 2 Server-PT devices
    • Click bottom toolbar → Switches → Drag 4 Switch 2960-24TT
    • Click bottom toolbar → End Devices → Drag 4 PCs (or mix with Laptops)
  • Position them as shown in Figure 4.3 (page 21 of lab manual)
  • Connect the devices: Use the "Automatically Choose Connection Type" cable (copper lightning bolt icon). Connect each PC to its respective switch, then connect all switches to both servers.
🔌 PCs connected to switches → switches to servers (trunk/access)
📌 Figure 4.3 reference: Topology with 4 switches, 2 servers, 4 end devices
2Configure IP Addresses for the Servers

Configure DHCP + DNS Server (Server0):

Click on Server0 → Desktop → IP Configuration
Set: IP: 192.168.100.10 | Mask: 255.255.255.0 | Gateway: 192.168.100.1 | DNS: 192.168.100.10

Configure HTTP + Email Server (Server1):

Click on Server1 → Desktop → IP Configuration
Set: IP: 192.168.100.20 | Mask: 255.255.255.0 | Gateway: 192.168.100.1
Server0 IP: 192.168.100.10 | Server1 IP: 192.168.100.20
📌 Like Figure 4.4 & 4.5 (pages 21-22)
3Configure DHCP Server
  • Click Server0 → Services → DHCP → Turn ON.
  • Default Gateway: 192.168.100.1
  • DNS Server: 192.168.100.10
  • Start IP Address: 192.168.100.50
  • Subnet Mask: 255.255.255.0
  • Maximum Users: 10 → Click Save.
DHCP Pool: 192.168.100.50 – 192.168.100.59
Gateway .1 | DNS .10
📌 Figure 4.6 (page 22): DHCP server configuration panel
4Configure IP Address Automatically (DHCP on PCs)

On each PC (PC0, PC1, PC2, PC3):

  • Desktop → IP Configuration → Select DHCP
  • Wait a few seconds: IP addresses will appear (192.168.100.50, .51, .52, .53).
PC0 gets 192.168.100.50
PC1 gets 192.168.100.51
PC2 gets 192.168.100.52
PC3 gets 192.168.100.53
📌 Figures 4.7–4.10 (pages 23-24): DHCP auto-configuration on PCs
5Configure DNS Server
  • Server0 → Services → DNS → Turn ON.
  • Add record: Name: www.puc.com → Address: 192.168.100.20 → Click Add/Save.
  • (Optional) Add mail.puc.com → 192.168.100.20 for email convenience.
nslookup www.puc.com
Server: [192.168.100.10]
Address: 192.168.100.20 ✅
📌 Figure 4.11–4.12 (pages 24-25): DNS record addition & verification
6Configure HTTP Server & Verify
  • Server1 → Services → HTTP → Turn ON.
  • Click New File: filename test.html → HTML content:
<html><body><h1>Welcome to PUC Network</h1><p>HTTP server is active!</p></body></html>
  • Save. Also create index.html if desired.
  • Verify: From any PC browser → http://192.168.100.20/test.html or http://www.puc.com/test.html → webpage displays.
✅ HTTP server: test.html loads successfully
📌 Figures 4.13–4.15 (pages 25-26): HTTP file creation & browser test
7Configure Email Server (SMTP/POP3)
  • Server1 → Services → EMAIL → Turn ON.
  • Add users: user1 / password password123 → click +.
  • Add user2 / password password123 → click +.
  • Domain (optional): puc.com → Save.
Users created: user1, user2
SMTP/POP3 ready on 192.168.100.20
📌 Figure 4.16 (page 27): Adding email users on server
8Configure Email Clients (PC1 & PC2)

PC1 (user1): Desktop → Email → Configure Mail:

Your Name: User One | Email: user1@puc.com
Incoming/Outgoing Server: 192.168.100.20 | Username: user1 | Password: password123 → Save

PC2 (user2): Desktop → Email → Configure Mail:

Your Name: User Two | Email: user2@puc.com
Incoming/Outgoing Server: 192.168.100.20 | Username: user2 | Password: password123 → Save
📌 Figures 4.17–4.18 (pages 27-28): Email client credential setup
9Test Email Service (Send & Receive)
  • On PC1: Compose email to user2@puc.com, subject "Hello", message "Testing email service". Click Send.
  • On PC2: Click Receive → email appears in inbox.
  • Reply from PC2 to user1@puc.com → PC1 clicks Receive → reply arrives.
✅ Email successfully delivered! SMTP & POP3 fully operational.
📧 user1 → user2 : email received ✅ | reply works ✅
📌 Figures 4.19–4.20 (pages 28-29): Compose email and successful receive

✅ Service Verification & Results

ServiceUser ActionExpected OutcomeStatus
DHCPTurn on PC → ipconfigIP 192.168.100.50–.53, gateway .1✓ Success
DNSnslookup www.puc.comReturns 192.168.100.20✓ Success
HTTPBrowser → http://www.puc.com/test.htmlWebpage displays welcome message✓ Success
SMTP (Send)PC1 sends email to user2@puc.com"Message sent" confirmation✓ Success
POP3 (Receive)PC2 clicks ReceiveEmail from user1 appears✓ Success
Full Email LoopPC2 replies → PC1 ReceiveTwo-way communication works✓ Success
💡 Insight: This lab demonstrates how DHCP, DNS, HTTP, and Email (SMTP/POP3) work together at the Application Layer. Users only see a browser or email client, while underlying protocols handle addressing, name resolution, and message delivery.

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Nazmul Islam Abir (43)
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