CS 372 - Ping and Traceroute

This document provides an overview of the IcmpHelperLibrary class and its key methods, focusing on the following functions:

1. __validateIcmpReplyPacketWithOriginalPingData
2. sendEchoRequest
3. __sendIcmpTraceRoute

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Overview of IcmpHelperLibrary

The IcmpHelperLibrary class is designed to handle ICMP (Internet Control Message Protocol) operations, such as sending ping requests and performing traceroute operations. It includes nested classes for managing ICMP packets (IcmpPacket) and handling ICMP Echo Replies (IcmpPacket_EchoReply).

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Key Functions

1. __validateIcmpReplyPacketWithOriginalPingData

Purpose:

This private method validates the received ICMP reply packet against the original ping request data to ensure the response is accurate.

Key Steps:

• Identifier Check: Compares the Identifier field of the reply packet with the original request.
• Sequence Number Check: Compares the Sequence Number field of the reply packet with the original request.
• Data Check: Compares the raw data in the reply packet with the original request data.
• Validation Result: Combines the results of the above checks to determine if the response is valid.

Debugging:

• If debugging is enabled, it prints the expected and actual values for each field and whether they match.
• If any field is invalid, it prints a detailed conflict message.

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2. sendEchoRequest

Purpose:

This method sends an ICMP Echo Request (ping) to a target host and handles the response.

Key Steps:

1. Target Validation: Ensures the target host and its IP address are set.
2. Socket Setup: Creates a raw socket for sending and receiving ICMP packets.
3. Packet Sending: Sends the ICMP Echo Request packet to the target host.
4. Response Handling:
   • Waits for a response using select.
   • Parses the received packet to determine the ICMP type and code.
   • Handles different ICMP types:
     • Type 11 (Time Exceeded): Prints a message with the error description.
     • Type 3 (Destination Unreachable): Prints a message with the error description.
     • Type 0 (Echo Reply): Validates the reply packet using __validateIcmpReplyPacketWithOriginalPingData and prints the result.
5. Timeout Handling: Prints a timeout message if no response is received within the specified time.

Return Value:

• Returns the Round-Trip Time (RTT) in milliseconds for successful Echo Replies (ICMP Type 0).
• Returns None for other ICMP types or timeouts.

Debugging:

• If debugging is enabled, it prints the ICMP packet header and data in hexadecimal format.

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3. __sendIcmpTraceRoute

Purpose:

This private method implements the traceroute functionality by incrementally increasing the Time-to-Live (TTL) value in ICMP packets to trace the route to a target host.

Key Steps:

1. Initialization:
   • Starts with a TTL of 1.
   • Sets a maximum number of hops (max_hops).
2. Packet Sending:
   • Builds an ICMP Echo Request packet for each TTL value.
   • Sends the packet and waits for a response.
3. Response Handling:
   • If the response is an Echo Reply (ICMP Type 0), the target host is reached, and the traceroute ends.
   • If the response is a Time Exceeded (ICMP Type 11), the TTL is incremented, and the process continues.
4. Termination:
   • Stops when the target host is reached or the maximum number of hops is exceeded.

Debugging:

• Prints the current TTL and whether the packet reached the target host.

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Supporting Classes

1. IcmpPacket

This nested class is responsible for constructing and managing ICMP packets.

Key Features:

• Packet Construction: Builds ICMP Echo Request packets with headers and data.
• Checksum Calculation: Ensures the integrity of the packet using a checksum.
• Packet Sending: Sends the constructed packet to the target host.

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2. IcmpPacket_EchoReply

This nested class handles ICMP Echo Reply packets.

Key Features:

• Packet Parsing: Extracts fields such as type, code, identifier, and sequence number from the received packet.
• Validation: Compares the received packet’s fields with the expected values.
• Result Printing: Displays the results of the ping operation, including RTT and validation status.

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Public Methods

sendPing(targetHost)

• Sends four ICMP Echo Requests to the specified target host.
• Prints RTT statistics (min, max, average) and packet loss percentage.

traceRoute(targetHost)

• Performs a traceroute to the specified target host.
• Prints the route taken by the packets, including intermediate hops.

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Example Usage

def main():
    icmpHelperPing = IcmpHelperLibrary()

    # Example: Send a ping to a target host
    icmpHelperPing.sendPing("www.google.com")

    # Example: Perform a traceroute to a target host
    icmpHelperPing.traceRoute("www.google.com")

if __name__ == "__main__":
    main()

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Error Descriptions

The getIcmpErrorDescription method provides human-readable descriptions for ICMP error codes. Examples include:

• (3,0): “Net Unreachable”
• (3,1): “Host Unreachable”
• (11,0): “Time to Live exceeded in Transit”

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This document summarizes the functionality of the IcmpHelperLibrary class and its key methods, providing a clear understanding of its ping and traceroute implementations.