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NAT - Network Address Translation, Types & Port Forwarding

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Steps

setup

Initialize Network Nodes and NAT Device

The network topology is set up with a client, NAT router, and external server. The NAT device is configured with a port forwarding rule mapping external port 8080 to internal IP 192.168.1.100 port 80.

💡 Setting up nodes and NAT rules is essential to simulate how packets will be translated and forwarded.

Line:

nat_device = NAT(public_ip='203.0.113.1')
nat_device.add_port_forwarding_rule(8080, '192.168.1.100', 80)

💡 The NAT device is ready to translate packets from the private network to the public network using port forwarding.

class Packet:
    def __init__(self, src_ip, src_port, dst_ip, dst_port, protocol):
        self.src_ip = src_ip
        self.src_port = src_port
        self.dst_ip = dst_ip
        self.dst_port = dst_port
        self.protocol = protocol

class NAT:
    def __init__(self, public_ip):
        self.public_ip = public_ip
        self.port_forwarding = {}
        self.nat_table = {}

    def add_port_forwarding_rule(self, external_port, internal_ip, internal_port):
        self.port_forwarding[external_port] = (internal_ip, internal_port)  # STEP 1

    def has_port_forwarding(self, port):
        return port in self.port_forwarding  # STEP 3

    def translate_packet(self, packet, new_src_ip=None, new_src_port=None, new_dst_ip=None, new_dst_port=None):
        # STEP 4 and 8
        if new_src_ip:
            packet.src_ip = new_src_ip
        if new_src_port:
            packet.src_port = new_src_port
        if new_dst_ip:
            packet.dst_ip = new_dst_ip
        if new_dst_port:
            packet.dst_port = new_dst_port
        return packet

    def update_nat_table(self, external_port, internal_ip, internal_port):
        self.nat_table[external_port] = (internal_ip, internal_port)  # STEP 4

    def lookup_nat_table(self, port):
        return self.nat_table.get(port, None)  # STEP 7

    def receive(self, packet):
        # STEP 3 and 7
        pass

    def send(self, packet, next_hop):
        # STEP 2, 5, 6, 9
        pass

# Simulation of packet flow
nat_device = NAT(public_ip='203.0.113.1')  # STEP 1
nat_device.add_port_forwarding_rule(8080, '192.168.1.100', 80)  # STEP 1

packet = Packet('192.168.1.100', 12345, '8.8.8.8', 80, 'TCP')  # STEP 2

# Client sends packet to NAT router
# NAT router receives and checks port forwarding
if nat_device.has_port_forwarding(8080):  # STEP 3
    translated_packet = nat_device.translate_packet(packet, new_src_ip='203.0.113.1', new_src_port=8080)  # STEP 4
    nat_device.update_nat_table(8080, '192.168.1.100', 80)  # STEP 4

# NAT router sends translated packet to server
# Server sends response back
response_packet = Packet('8.8.8.8', 80, '203.0.113.1', 8080, 'TCP')  # STEP 6

nat_entry = nat_device.lookup_nat_table(response_packet.dst_port)  # STEP 7
if nat_entry:
    internal_ip, internal_port = nat_entry
    translated_response = nat_device.translate_packet(response_packet, new_dst_ip=internal_ip, new_dst_port=12345)  # STEP 8

# NAT router sends translated response to client
# Client receives response

📊

NAT - Network Address Translation, Types & Port Forwarding - Watch the Algorithm Execute, Step by Step

Watching the packet flow and NAT translation step-by-step reveals how NAT modifies packet headers and manages port mappings, which is difficult to grasp from code or static diagrams alone.

Step 1/10

·Active fill★Answer cell

Network nodes initialized and NAT port forwarding rule configured.

Hop: 0

Client 192.168.1.100

NAT Router 203.0.113.1

Server 8.8.8.8

Practice

(1/5)

1. Trace the sequence of events when a client sends a request to a web server protected by a reverse proxy. Which step happens immediately after the reverse proxy receives the client request?

easy

A. The reverse proxy forwards the request to the backend server

B. The firewall inspects and blocks the request if malicious

C. The proxy server caches the response for future requests

D. The client directly connects to the backend server

NAT - Network Address Translation, Types & Port Forwarding

Start learning this pattern below

Initialize Network Nodes and NAT Device

Client Sends Packet to External Server

NAT Router Receives Packet and Checks Port Forwarding Rules

NAT Router Translates Source IP and Port (Port Forwarding)

NAT Router Sends Translated Packet to External Server

Server Receives Packet and Sends Response

NAT Router Receives Response and Looks Up NAT Table

NAT Router Translates Destination IP and Port Back to Internal Client

NAT Router Forwards Translated Response to Internal Client

Client Receives Response Packet

Key Takeaways

Practice

Solution

Step 1: Understand reverse proxy role

Step 2: After receiving the request

Step 3: Other options

Final Answer:

Quick Check:

Solution

Step 1: Understand the safety property of HTTP methods

Step 2: Analyze other methods

Final Answer:

Quick Check:

Solution

Step 1: Understand encapsulation order in TCP/IP model

Final Answer:

Quick Check:

Solution

Step 1: Understand the handshake steps

Step 2: Evaluate each option

Final Answer:

Quick Check:

Solution

Step 1: Identify handshake latency cause

Step 2: Analyze options

Final Answer:

Quick Check: