以太网头部14 bytes
Destination
Source
Len
Data unit + pad
FCS
(6 bytes)
(6 bytes)
(2)
(46-1500 bytes)
(4 bytes)
Ethernet header structure
ARP数据包括14字节的以太网头部和28字节的数据
IP头部20 bytes
4
8
16
32 bits
Ver.
IHL
Type of service
Total length Identification
Flags
Fragment offset Time to live
Protocol Header checksum
Source address
Destination address
Option + Padding
Data
IP header structure
TCP头部20 bytes
16
32 bits
Source port
Destination port Sequence number
Acknowledgement number
Offset
Resrvd
U
A
P
R
S
F
Window
Checksum
Urgent pointer
Option + Padding
Data
TCP header structure
UDP头部8 bytes
16
32 bits
Source port
Destination port
Length
Checksum
DataUDP header structure
网络协议结构体定义:
// i386 is little_endian.
#ifndef LITTLE_ENDIAN
#define LITTLE_ENDIAN (1) //BYTE ORDER
#else
#error Redefine LITTLE_ORDER
#endif
//Mac头部，总长度14字节
typedef struct _eth_hdr
{
unsigned char dstmac[6]; //目标mac地址
unsigned char srcmac[6]; //源mac地址
unsigned short eth_type; //以太网类型
}eth_hdr;
//IP头部，总长度20字节
typedef struct _ip_hdr
{
#if LITTLE_ENDIAN
unsigned char ihl:4; //首部长度
unsigned char version:4, //版本
#else
unsigned char version:4, //版本
unsigned char ihl:4; //首部长度
#endif
unsigned char tos; //服务类型
unsigned short tot_len; //总长度
unsigned short id; //标志
unsigned short frag_off; //分片偏移
unsigned char ttl; //生存时间
unsigned char protocol; //协议
unsigned short chk_sum; //检验和
struct in_addr srcaddr; //源IP地址
struct in_addr dstaddr; //目的IP地址
}ip_hdr;
//TCP头部，总长度20字节
typedef struct _tcp_hdr
{
unsigned short src_port; //源端口号
unsigned short dst_port; //目的端口号
unsigned int seq_no; //序列号
unsigned int ack_no; //确认号
#if LITTLE_ENDIAN
unsigned char reserved_1:4; //保留6位中的4位首部长度
unsigned char thl:4; //tcp头部长度
unsigned char flag:6; //6位标志
unsigned char reseverd_2:2; //保留6位中的2位
#else
unsigned char thl:4; //tcp头部长度
unsigned char reserved_1:4; //保留6位中的4位首部长度
unsigned char reseverd_2:2; //保留6位中的2位
unsigned char flag:6; //6位标志
#endif
unsigned short wnd_size; //16位窗口大小
unsigned short chk_sum; //16位TCP检验和
unsigned short urgt_p; //16为紧急指针
}tcp_hdr;
//UDP头部，总长度8字节
typedef struct _udp_hdr
{
unsigned short src_port; //远端口号
unsigned short dst_port; //目的端口号
unsigned short uhl; //udp头部长度
unsigned short chk_sum; //16位udp检验和
}udp_hdr;
//ICMP头部，总长度4字节
typedef struct _icmp_hdr
{
unsigned char icmp_type; //类型
unsigned char code; //代码
unsigned short chk_sum; //16位检验和
}icmp_hdr;
//ARP头部，总长度8字节
* ARP protocol opcodes. */
#define ARPOP_REQUEST 1 /* ARP request */
#define ARPOP_REPLY 2 /* ARP reply */
#define ARPOP_RREQUEST 3 /* RARP request */
#define ARPOP_RREPLY 4 /* RARP reply */
/*
* This structure defines an ethernet arp header.
*/
struct arphdr
{
unsigned short ar_hrd; /* format of hardware address */
unsigned short ar_pro; /* format of protocol address */
unsigned char ar_hln; /* length of hardware address */
unsigned char ar_pln; /* length of protocol address */
unsigned short ar_op; /* ARP opcode (command) */
#if 0
/*
* Ethernet looks like this : This bit is variable sized however...
*/
unsigned char ar_sha[ETH_ALEN]; /* sender hardware address */
unsigned char ar_sip[4]; /* sender IP address */
unsigned char ar_tha[ETH_ALEN]; /* target hardware address */
unsigned char ar_tip[4]; /* target IP address */
#endif
};全面的网络协议结构体定义:
/*********************************************/
//计算机网络各种协议的结构
#define ETHER_ADDR_LEN 6 //NIC物理地址占6字节
#define MAXDATA 10240
/*
网络实验程序
数据包中的TCP包头,IP包头,UDP包头,ARP包,Ethernet包等.
以及各种表.路由寻址表,地址解析协议表DNS表等
*/
#define ETHERTYPE_IP 0x0800 //IP Protocal
#define ETHERTYPE_ARP 0x0806 //Address Resolution Protocal
#define ETHERTYPE_REVARP 0x0835 //Reverse Address Resolution Protocal 逆地址解析协议
/*********************************************/
//ethernet
typedef struct ether_header
{
u_char ether_dhost[ETHER_ADDR_LEN];
u_char ether_shost[ETHER_ADDR_LEN];
u_short ether_type;
}ETH_HEADER;
/*********************************************/
//ether_header eth;
/*********************************************/
//arp
typedef struct arphdr
{
u_short ar_hrd;
u_short ar_pro;
u_char ar_hln;
u_char ar_pln;
u_short ar_op;
}ARP_HEADER;
/*********************************************/
/*********************************************/
//IP报头
typedef struct ip
{
u_int ip_v:4; //version(版本)
u_int ip_hl:4; //header length(报头长度)
u_char ip_tos;
u_short ip_len;
u_short ip_id;
u_short ip_off;
u_char ip_ttl;
u_char ip_p;
u_short ip_sum;
struct in_addr ip_src;
struct in_addr ip_dst;
}IP_HEADER;
/*********************************************/
/*********************************************/
//TCP报头结构体
typedef struct tcphdr
{
u_short th_sport;
u_short th_dport;
u_int th_seq;
u_int th_ack;
u_int th_off:4;
u_int th_x2:4;
u_char th_flags;
u_short th_win;
u_short th_sum;
u_short th_urp;
}TCP_HEADER;
#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
#define TH_PUSH 0x08
#define TH_ACK 0x10
#define TH_URG 0x20
/*********************************************/
/*********************************************/
//UDP报头结构体*/
typedef struct udphdr
{
u_short uh_sport;
u_short uh_dport;
u_short uh_ulen;
u_short uh_sum;
}UDP_HEADER;
/*********************************************/
//=============================================
/*********************************************/
/*ARP与ETHERNET生成的报头*/
typedef struct ether_arp
{
struct arphdr ea_hdr;
u_char arp_sha[ETHER_ADDR_LEN];
u_char arp_spa[4];
u_char arp_tha[ETHER_ADDR_LEN];
u_char arp_tpa[4];
}ETH_ARP;
#define arp_hrd ea_hdr.ar_hrd
#define arp_pro ea_hdr.ar_pro
#define arp_hln ea_hdr.ar_hln
#define arp_pln ea_hdr.ar_pln
#define arp_op ea_hdr.ar_op
#define ARPHRD 1
/*********************************************/
/*********************************************/
//tcp与ip生成的报头
typedef struct packet_tcp
{
struct ip ip;
struct tcphdr tcp;
u_char data[MAXDATA];
}TCP_IP;
/*********************************************/
/*********************************************/
//udp与ip生成的报头
typedef struct packet_udp
{
struct ip ip;
struct udphdr udp;
}UDP_IP;
/*********************************************/
/*********************************************/
//ICMP的各种形式
//icmpx,x==icmp_type;
//icmp报文(能到达目的地,响应-请求包)
struct icmp8
{
u_char icmp_type; //type of message(报文类型)
u_char icmp_code; //type sub code(报文类型子码)
u_short icmp_cksum;
u_short icmp_id;
u_short icmp_seq;
char icmp_data[1];
};
//icmp报文(能返回目的地,响应-应答包)
struct icmp0
{
u_char icmp_type; //type of message(报文类型)
u_char icmp_code; //type sub code(报文类型子码)
u_short icmp_cksum;
u_short icmp_id;
u_short icmp_seq;
char icmp_data[1];
};
//icmp报文(不能到达目的地)
struct icmp3
{
u_char icmp_type; //type of message(报文类型)
u_char icmp_code; //type sub code(报文类型子码),例如:0网络原因不能到达,1主机原因不能到达...
u_short icmp_cksum;
u_short icmp_pmvoid;
u_short icmp_nextmtu;
char icmp_data[1];
};
//icmp报文(重发结构体)
struct icmp5
{
u_char icmp_type; //type of message(报文类型)
u_char icmp_code; //type sub code(报文类型子码)
u_short icmp_cksum;
struct in_addr icmp_gwaddr;
char icmp_data[1];
};
struct icmp11
{
u_char icmp_type; //type of message(报文类型)
u_char icmp_code; //type sub code(报文类型子码)
u_short icmp_cksum;
u_int icmp_void;
char icmp_data[1];
};