网络协议
这个七层协议或者五层协议相信大家都很清楚,那么每一层分别做了什么?
网络每层做了什么事情
传输层
传输层添加下面这八个字节的数据内容(TCP协议)
网络层
网络层添加下面指示的这20个字节的数据内容(IP协议)
链路层
链路层添加下图开头的14个字节(以太网协议)
抓包工具
- raw-socket
- netmap
- dpdk
code
头文件
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/poll.h>
#include <arpa/inet.h>
#define NETMAP_WITH_LIBS
#include <net/netmap_user.h>
UDP协议
#pragma pack(1)
#define ETH_ALEN 6
struct ethhdr {
unsigned char h_dest[ETH_ALEN];
unsigned char h_source[ETH_ALEN];
unsigned short h_proto;
};
struct iphdr {
unsigned char version;
unsigned char tos;
unsigned short tot_len;
unsigned short id;
unsigned short flag_off;
unsigned char ttl;
unsigned char protocol;
unsigned short check;
unsigned int saddr;
unsigned int daddr;
};
struct udphdr {
unsigned short source;
unsigned short dest;
unsigned short len;
unsigned short check;
};
struct udppkt {
struct ethhdr eh;
struct iphdr ip;
struct udphdr udp;
unsigned char body[0];
};
收发数据
void echo_udp_pkt(struct udppkt *udp, struct udppkt *udp_rt) {
memcpy(udp_rt, udp, sizeof(struct udppkt));
memcpy(udp_rt->eh.h_dest, udp->eh.h_source, ETH_ALEN);
memcpy(udp_rt->eh.h_source, udp->eh.h_dest, ETH_ALEN);
udp_rt->ip.saddr = udp->ip.daddr;
udp_rt->ip.daddr = udp->ip.saddr;
udp_rt->udp.source = udp->udp.dest;
udp_rt->udp.dest = udp->udp.source;
}
int main() {
struct ethhdr *eh;
struct pollfd pfd = {
0};
struct nm_pkthdr h;
unsigned char *stream = NULL;
struct nm_desc *nmr = nm_open("netmap:eth0", NULL, 0, NULL);
if (nmr == NULL) {
return -1;
}
pfd.fd = nmr->fd;
pfd.events = POLLIN;
while (1) {
int ret = poll(&pfd, 1, -1);
if (ret < 0) continue;
if (pfd.revents & POLLIN) {
stream = nm_nextpkt(nmr, &h);
eh = (struct ethhdr*)stream;
if (ntohs(eh->h_proto) == PROTO_IP) {
struct udppkt *udp = (struct udppkt*)stream;
if (udp->ip.protocol == PROTO_UDP) {
struct in_addr addr;
addr.s_addr = udp->ip.saddr;
int udp_length = ntohs(udp->udp.len);
printf("%s:%d:length:%d, ip_len:%d --> ", inet_ntoa(addr), udp->udp.source,
udp_length, ntohs(udp->ip.tot_len));
udp->body[udp_length-8] = '\0';
printf("udp --> %s\n", udp->body);
#if 1
struct udppkt udp_rt;
echo_udp_pkt(udp, &udp_rt);
nm_inject(nmr, &udp_rt, sizeof(struct udppkt));
#endif
} else {
printf("other ip packet");
}
}
}
}
}