365 Days of Code - Day 049

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/**
 * ip_stack.h
 *
 * @brief RFC implementation of the IP protocol
 * IPv4: RFC 791
 * IPv6: RFC 8200
 */

#ifndef IP_STACK_H
#define IP_STACK_H

#include <stdint.h>

/**
 * @enum ip_version
 * @brief Version identifiers.
 */
enum ip_version
{
    IPV4 = 4,
    IPV6 = 6
};

/**
 * @enum ip_protocol
 * @brief Upper-layer protocol identifiers.
 */
enum ip_protocol
{
    IP_PROTO_ICMP = 1 /** Internet Control Message Protocol */
};

/**
 * @struct ipv4_header
 * @brief 20-byte IPv4 header, packed wire layout, without options.
 *
 * @ref RFC 791
 */
struct ipv4_header
{
    uint8_t version_ihl;     /** IP Version (4 bits) + Internet Header Length (4 bits) */
    uint8_t type_of_service; /** DSCP+ECN - See RFC 2474 (DSCP), RFC 3168 (ECN) and their respective updates */
    uint16_t total_length;   /** Length of complete datagram, in octets. Absolute Max: 65535, Recommended Max: 576 */
    uint16_t id;             /** Aids in reassembly of fragments */
    uint16_t flags_offset;   /** Flags (3 bits) + Fragment Offset (13 bits) */
    uint8_t ttl;             /** Time to Live a.k.a. hop count */
    uint8_t protocol;        /** Upper-layer protocol id */
    uint16_t checksum;       /** Ones' complement checksum of all 16-bit words in the header */
    uint32_t src;            /** Source address */
    uint32_t dst;            /** Destination address */
} __attribute__((packed));

/**
 * @struct ipv6_header
 * @brief 40-byte IPv6 header, packed wire layout, without extensions.
 *
 * @ref RFC 8200
 */
struct ipv6_header
{
    uint32_t version_class_flow; /** IP Version (4 bits) + Traffic Class (8 bits) + Flow Label (20 bits) */
    uint16_t payload_length;     /** Length of the packet following this header (extension headers + payload) */
    uint8_t next_header;         /** ID of the type of header following this header */
    uint8_t hop_limit;           /** Hop limit (TTL in IPv4) */
    uint8_t src[16];             /** Source address (128-bit) */
    uint8_t dst[16];             /** Destination address (128-bit) */
} __attribute__((packed));

#endif /* IP_STACK_H */

1

sudo apt install doxygen doxygen-doc doxygen2man

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doxygen -g
doxygen Doxyfile
cd html
python3 -m http.server 3000

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struct ipv6_header
{
    uint32_t version_class_flow; /**< IP Version (4 bits) + Traffic Class (8 bits) + Flow Label (20 bits) */
    uint16_t payload_length;     /**< Length of the packet following this header (extension headers + payload) */
<snip>

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/**
 * ip_common.h
 *
 * @brief Shared components and parameters for IPv4 and IPv6 protocols
 * IPv4: RFC 791
 * IPv6: RFC 8200
 */

#ifndef IP_COMMON_H
#define IP_COMMON_H

enum ip_version
{
    IPV4 = 4,
    IPV6 = 6
};

enum ip_protocol
{
    IP_PROTO_ICMPV4 = 1,
    IP_PROTO_ICMPV6 = 58
};

#endif /* IP_COMMON_H */

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/**
 * ipv4.h
 *
 * @brief RFC implementation of the IP protocol
 * IPv4: RFC 791
 */

#ifndef IPV4_H
#define IPV4_H

#include <stdint.h>
#include "ip_common.h"

/**
 * @brief Absolute max IPv4 datagram length (header + payload) in octets.
 */
#define IPV4_MAX_PACKET_SIZE 65535

/**
 * @brief Minimum datagram size all hosts must be prepared to accept.
 */
#define IPV4_RECOMMENDED_MTU 576

/**
 * @brief Minimum valid Internet Header Length in 32-bit words (20 bytes).
 */
#define IPV4_MIN_IHL 5

/**
 * @struct ipv4_header
 * @brief 20-byte IPv4 header, packed wire layout, without options.
 *
 * @note RFC 791
 */
struct ipv4_header
{
    uint8_t version_ihl;     /**< IP Version (4 bits) + Internet Header Length (4 bits) */
    uint8_t type_of_service; /**< DSCP+ECN - See RFC 2474 (DSCP), RFC 3168 (ECN) and their respective updates */
    uint16_t total_length;   /**< Length of complete datagram, in octets. Absolute Max: 65535, Recommended Max: 576 */
    uint16_t id;             /**< Aids in reassembly of fragments */
    uint16_t flags_offset;   /**< Flags (3 bits) + Fragment Offset (13 bits) */
    uint8_t ttl;             /**< Time to Live a.k.a. hop count */
    uint8_t protocol;        /**< Upper-layer protocol id */
    uint16_t checksum;       /**< Ones' complement checksum of all 16-bit words in the header */
    uint32_t src;            /**< Source address */
    uint32_t dst;            /**< Destination address */
} __attribute__((packed));

#endif /* IPV4_H */

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/**
 * ipv6.h
 *
 * @brief RFC implementation of the IPv6 protocol
 * IPv6: RFC 8200
 */

#ifndef IPV6_H
#define IPV6_H

#include <stdint.h>
#include "ip_common.h"

/**
 * @brief The absolute minimum link MTU required for any IPv6 network.
 */
#define IPV6_MIN_LINK_MTU 1280

/**
 * @brief The minimum fragment reassembly size all IPv6 nodes must support.
 */
#define IPV6_MIN_REASSEMBLY_SIZE 1500

/**
 * @brief The fixed length of the base IPv6 header in octets (40 bytes).
 */
#define IPV6_BASE_HEADER_LENGTH 40

/**
 * @struct ipv6_header
 * @brief 40-byte IPv6 header, packed wire layout, without extensions.
 *
 * @note RFC 8200
 */
struct ipv6_header
{
    uint32_t version_class_flow; /**< IP Version (4 bits) + Traffic Class (8 bits) + Flow Label (20 bits) */
    uint16_t payload_length;     /**< Length of the packet following this header (extension headers + payload) */
    uint8_t next_header;         /**< ID of the type of header following this header */
    uint8_t hop_limit;           /**< Hop limit (TTL in IPv4) */
    uint8_t src[16];             /**< Source address (128-bit) */
    uint8_t dst[16];             /**< Destination address (128-bit) */
} __attribute__((packed));

#endif /* IPV6_H */