Firewalls and packet filtering in Computer Networks - Mini Project: Build & Apply

Understanding Firewalls and Packet Filtering

📖 Scenario: You are learning how a firewall protects a home network by controlling which data packets can enter or leave.Imagine a firewall as a security guard checking each data packet against rules before allowing it through.

🎯 Goal: Build a simple list of data packets and a set of filtering rules, then apply the rules to decide which packets are allowed or blocked.

📋 What You'll Learn

Create a list of data packets with specific source IPs and destination ports

Define a configuration variable for allowed destination ports

Use a loop to filter packets based on allowed ports

Mark each packet as 'allowed' or 'blocked' according to the filtering

💡 Why This Matters

🌍 Real World

Firewalls protect home and business networks by controlling which data packets can pass through based on rules.

💼 Career

Network administrators and cybersecurity professionals configure firewalls and packet filters to secure systems from unauthorized access.

1

Create the list of data packets

Create a list called packets with these exact dictionaries representing data packets: {'src_ip': '192.168.1.10', 'dst_port': 80}, {'src_ip': '10.0.0.5', 'dst_port': 22}, {'src_ip': '172.16.0.3', 'dst_port': 443}, {'src_ip': '192.168.1.15', 'dst_port': 25}

Computer Networks

# Create the list called packets with the specified dictionaries
# Your code here

Need a hint?

Use a list with dictionaries. Each dictionary has keys 'src_ip' and 'dst_port'.

2

Define allowed destination ports

Create a list called allowed_ports containing these exact port numbers: 80, 443

Computer Networks

packets = [
    {'src_ip': '192.168.1.10', 'dst_port': 80},
    {'src_ip': '10.0.0.5', 'dst_port': 22},
    {'src_ip': '172.16.0.3', 'dst_port': 443},
    {'src_ip': '192.168.1.15', 'dst_port': 25}
]
# Create the list allowed_ports with 80 and 443
# Your code here

Need a hint?

Use a list with the numbers 80 and 443 exactly.

3

Filter packets based on allowed ports

Create a new list called filtered_packets that contains only the packets from packets where the dst_port is in allowed_ports. Use a for loop with the variable packet to check each packet.

Computer Networks

packets = [
    {'src_ip': '192.168.1.10', 'dst_port': 80},
    {'src_ip': '10.0.0.5', 'dst_port': 22},
    {'src_ip': '172.16.0.3', 'dst_port': 443},
    {'src_ip': '192.168.1.15', 'dst_port': 25}
]
allowed_ports = [80, 443]
# Create filtered_packets list using a for loop and check dst_port
# Your code here

Need a hint?

Start with an empty list filtered_packets. Use a for loop to check each packet's dst_port. Append allowed packets to the new list.

4

Mark packets as allowed or blocked

Create a new list called final_packets where each packet from packets has an added key 'status' with the value 'allowed' if its dst_port is in allowed_ports, otherwise 'blocked'. Use a for loop with the variable packet.

Computer Networks

packets = [
    {'src_ip': '192.168.1.10', 'dst_port': 80},
    {'src_ip': '10.0.0.5', 'dst_port': 22},
    {'src_ip': '172.16.0.3', 'dst_port': 443},
    {'src_ip': '192.168.1.15', 'dst_port': 25}
]
allowed_ports = [80, 443]
filtered_packets = []
for packet in packets:
    if packet['dst_port'] in allowed_ports:
        filtered_packets.append(packet)
# Create final_packets list with status key added to each packet
# Your code here

Need a hint?

Copy each packet dictionary to avoid changing the original. Add a 'status' key with 'allowed' or 'blocked' based on the port.