struct ethhdr、ether_header、iphdr、tcphdr、udphdr

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本文深入解析以太网、IP、TCP、UDP协议的关键结构，包括以太网头部、IP头部、TCP头部和UDP头部的重要字段及作用。

************************eth的结构**************************************

struct ethhdr {
unsigned char h_dest[ETH_ALEN];
unsigned char h_source[ETH_ALEN];
__be16 h_proto;
} __attribute__((packed));

struct ether_header
{
u_int8_t ether_dhost[ETH_ALEN];      // destination eth addr
u_int8_t ether_shost[ETH_ALEN];      // source ether addr
u_int16_t ether_type;                 // packet type ID field
} __attribute__ ((__packed__));

***********************IP的结构***********************************
struct iphdr
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned int ihl:4;
    unsigned int version:4;
#elif __BYTE_ORDER == __BIG_ENDIAN
    unsigned int version:4;
    unsigned int ihl:4;
#else
# error "Please fix <bits/endian.h>"
#endif
    u_int8_t tos;
    u_int16_t tot_len;
    u_int16_t id;
    u_int16_t frag_off;
    u_int8_t ttl;
    u_int8_t protocol;
    u_int16_t check;
    u_int32_t saddr;
    u_int32_t daddr;
};

***********************TCP的结构****************************
struct tcphdr
{
    u_int16_t source;
    u_int16_t dest;
    u_int32_t seq;
    u_int32_t ack_seq;
# if __BYTE_ORDER == __LITTLE_ENDIAN
    u_int16_t res1:4;
    u_int16_t doff:4;
    u_int16_t fin:1;
    u_int16_t syn:1;
    u_int16_t rst:1;
    u_int16_t psh:1;
    u_int16_t ack:1;
    u_int16_t urg:1;
    u_int16_t res2:2;
# elif __BYTE_ORDER == __BIG_ENDIAN
    u_int16_t doff:4;
    u_int16_t res1:4;
    u_int16_t res2:2;
    u_int16_t urg:1;
    u_int16_t ack:1;
    u_int16_t psh:1;
    u_int16_t rst:1;
    u_int16_t syn:1;
    u_int16_t fin:1;
# else
#   error "Adjust your <bits/endian.h> defines"
# endif
    u_int16_t window;
    u_int16_t check;
    u_int16_t urg_ptr;
};
***********************UDP的结构*****************************
struct udphdr
{
u_int16_t source;
u_int16_t dest;
u_int16_t len;
u_int16_t check;
};