Layered Model and Addressing Lab

Retrieval Prompts

1. Name the five layers of the Internet stack in order, with the unit of data at each.
2. Describe encapsulation in one sentence without using the word "stack."
3. State the difference between MAC, IP, and DNS as identifiers.
4. State the rule for deciding whether two IPv4 addresses are on the same subnet.
5. State what NAT does in one sentence.

Compare and Distinguish

Separate these pairs clearly:

• MAC address versus IP address
• subnet mask versus CIDR prefix length
• routing versus switching
• DNS name versus IP address versus port
• header versus payload

Common Mistake Check

For each statement, identify the error:

1. "My MAC address identifies my laptop on the Internet."
2. "10.0.24.53/20 includes 10.0.33.10, because they start the same way."
3. "NAT is a firewall."
4. "DNS resolution happens in the kernel, like TCP does."
5. "Encapsulation adds headers only at the transport layer."

Mini Application

For each scenario, do all four tasks:

1. Identify which layer is dominant.
2. Name the identifiers involved (MAC, IP, port, DNS name).
3. Describe what a packet on the wire looks like, header by header.
4. Say what would break if one of the lower layers behaved incorrectly.

Scenarios:

1. A laptop on Wi-Fi runs curl https://api.example.com/health.
2. An IPv4 host pings 8.8.8.8.
3. Two containers on the same Docker bridge network talk to each other by service name.
4. A laptop on cellular reuses the same DNS result but cannot establish a TCP connection.

Subnet Math Workshop

Solve without a calculator. Show the mask in dotted-decimal.

#	CIDR	Network	Broadcast	Usable range	Hosts
1	192.168.1.100/24
2	172.16.5.200/20
3	10.20.30.40/28
4	203.0.113.65/26
5	10.0.24.53/20

Then, for row 5, decide membership for each of: 10.0.16.1, 10.0.31.254, 10.0.32.0, 10.0.47.10.

Evidence Check

This page is complete only if you can walk a packet from an application call to bits on a wire and back, naming the header added or removed at each layer.