Router Program

This repository contains a simple router implementation in C. The program handles basic routing and ARP requests and replies, and is designed for educational purposes.

Files

• router.c: The main file containing the router implementation.
• queue.h, lib.h, protocols.h, router.h: Header files required for the router's functionality.
• rtable_out.txt, arp_table_static.txt: Example files for routing and ARP tables.

Functionality

The router performs the following key tasks:

1. Initialization: Initializes routing and ARP tables, reads routing table from file, and prints it.
2. Packet Reception: Listens for incoming packets on all interfaces.
3. Packet Processing: Handles ARP and IP packets:
   • ARP requests and replies.
   • IP packet forwarding, ICMP echo requests and replies, and ICMP error messages.
4. Routing Table Management: Finds the best route for an IP packet.
5. ARP Table Management: Manages ARP table entries.

Structure

Main Function

The main function initializes the router, reads the routing table, creates queues, and enters an infinite loop to process incoming packets.

ARP Handling

• ARP Requests: Generates and sends ARP replies.
• ARP Replies: Updates the ARP table and processes queued packets waiting for the ARP reply.

IP Packet Handling

• ICMP Echo Requests: Replies with ICMP Echo Replies.
• ICMP Errors: Sends ICMP Time Exceeded or Destination Unreachable messages.
• IP Forwarding: Forwards IP packets to the next hop based on the routing table.

Helper Functions

• add_to_arp_table: Adds an entry to the ARP table.
• print_rtable: Prints the routing table to a file.
• comparePrefix: Compares two routing table entries by prefix and mask.
• get_best_route: Finds the best route for a given IP address.
• get_arp_table_entry: Finds an ARP table entry for a given IP address.