TCP/IP Network Protocols
How data moves through a TCP/IP network
TCP/IP Network Protocols
How data moves through a TCP/IP network
Lesson objectives
• Explain the purpose of each TCP/IP layer.
• Identify common protocols and explain what each does.
• Describe how data moves through the TCP/IP stack.
• Use Packet Tracer to observe ARP, TCP and HTTP.
• Use Wireshark to identify DNS and TCP traffic.
• Apply protocol knowledge to realistic scenarios.
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Retrieval starter
5–10 minutes • Answer individually
• What OSI layer is responsible for routing?
• What does DNS do?
• What does DHCP do?
• What are SYN, SYN-ACK and ACK?
• Which protocol is commonly used to transfer web pages?
• Why can the first ping sometimes time out?
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The TCP/IP model
Application
HTTP • HTTPS • DNS • DHCP • FTP • SFTP • SMTP • POP • IMAP
Transport
TCP • UDP
Internet
IP • ICMP
Network Access
Ethernet • Wi‑Fi • ARP
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TCP/IP and OSI mapping
TCP/IP
Application
TCP/IP
Transport
TCP/IP
Internet
TCP/IP
Network Access
• Application ≈ OSI 5, 6 and 7
• Transport = OSI 4
• Internet = OSI 3
• Network Access ≈ OSI 1 and 2
• Use the models to describe functions and protocols; they are not identical models.
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Web protocols
• HTTP — transfers web resources; commonly port 80.
• HTTPS — HTTP protected using TLS; commonly port 443.
• HTTP/HTTPS operate at the TCP/IP Application layer.
• TCP provides reliable transport underneath a typical HTTP/HTTPS connection.
• IP provides addressing and routing; Ethernet/Wi‑Fi carries frames on each local link.
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Email protocols
SMTP
SEND / RELAY
POP
RETRIEVE / DOWNLOAD
IMAP
ACCESS / SYNCHRONISE
• SMTP is used to send/relay email.
• POP traditionally downloads messages to a client.
• IMAP keeps email on the server and synchronises access across devices.
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Routing protocols
• RIP — exchanges routing information and uses hop count as its metric.
• OSPF — a link-state routing protocol that uses a cost metric and builds topology information.
• Routing protocols help routers learn routes to networks.
• Do not confuse routing protocols with the protocols that carry application data.
Routing decision → IP forwarding → next network link
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Other protocols to know
• FTP — file transfer.
• SFTP — secure file transfer over SSH.
• DHCP — automatically provides network configuration such as an IP address.
• DNS — translates domain names into IP addresses.
• TCP — reliable, connection-oriented transport.
• UDP — connectionless transport with lower overhead.
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How a webpage request works
1
DNS
name → IP
2
TCP
SYN / SYN-ACK / ACK
3
HTTP/HTTPS
request
4
IP
routing
5
Ethernet/Wi‑Fi
local delivery
• The exact sequence depends on the application and configuration.
• The layers cooperate rather than operating independently.
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Practical 1 — Packet Tracer
25 minutes
• Switch to Simulation Mode.
• Edit Filters → Show None.
• Enable ARP, TCP and HTTP.
• On the R1-side PC, open Web Browser.
• Browse to http://192.168.10.2 (or your configured server name).
• Use Capture/Forward and inspect PDU Details.
• Record what you observe.
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Packet Tracer — what to record
• ARP: What IP address is being resolved to a MAC address?
• TCP: Identify SYN, SYN-ACK and ACK.
• HTTP: Identify the request and response.
• IP: Record source and destination IP addresses.
• Layer 2: What happens to MAC addresses at a router?
• Which TCP/IP layer does each protocol belong to?
Challenge: Why can the MAC addresses change at each router while the destination IP remains the same?
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Key observation — routers
• IP addresses support end-to-end routing.
• MAC addresses are used for local link delivery.
• A router receives a frame and examines the Layer 3 destination.
• It then creates a new Layer 2 frame for the next link.
• Therefore the Layer 2 addresses can change from hop to hop.
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Practical 2 — Wireshark
25 minutes • authorised traffic only
• Start a capture on an interface you are authorised to monitor.
• Generate suitable traffic — for example, visit a known test site.
• Use display filters: dns, tcp, http.
• Find a DNS query and response.
• Find a TCP three-way handshake.
• Look for an HTTP request/response if HTTP traffic is available.
• Record evidence and map each item to TCP/IP.
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Wireshark investigation table
DNS
Query name + returned IP
TCP
Source/destination ports + SYN/SYN-ACK/ACK
HTTP
Request method + response if visible
Layer
TCP/IP layer + reason
• If HTTPS is used, students may see TLS traffic rather than readable HTTP content.
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Protocol challenge
10 minutes
• A new laptop needs an IP address automatically → ?
• A user types a website name → ?
• A user sends an email → ?
• A user wants the same mailbox synchronised on several devices → ?
• A company needs secure file transfer → ?
• Routers need to exchange route information → ?
DHCP • DNS • SMTP • IMAP • SFTP • RIP/OSPF
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Assessment questions
• 1. Explain the purpose of the TCP/IP Application layer. [2]
• 2. Explain one difference between HTTP and HTTPS. [2]
• 3. Explain the purpose of DNS and DHCP. [4]
• 4. Explain the difference between SMTP, POP and IMAP. [4]
• 5. Explain how HTTP, TCP and IP work together when a webpage is accessed. [6]
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Model structure for the 6-mark question
• Start with the application: HTTP/HTTPS requests a web resource.
• DNS may resolve the website name to an IP address.
• TCP establishes a connection and provides reliable transport.
• IP provides logical addressing and routers forward packets towards the destination.
• Ethernet/Wi‑Fi provides local frame delivery on each link.
• At the destination, the data is passed back up the stack to the application.
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Exit ticket
5 minutes
• Name one web protocol.
• Name the protocol used to send email.
• What does DNS do?
• What does DHCP do?
• What is the purpose of TCP?
• In one sentence, explain how data moves through the TCP/IP stack.
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Key takeaways
Application
What service is being used?
Transport
How is data delivered?
Internet
Where should it go?
Network Access
How does it cross this local link?
• Know the protocol → know its purpose → identify it in traffic → explain how it contributes to communication.
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