为什么 echo ping 没有到达目的地？
Why is the echo ping not reaching the destination?
我正在尝试使用 Raw Socket 自己实现一个 ICMP echo ping 数据包。在我的 Linux 机器上进行 tcpdump 时，我发现 Echo ping 请求已成功发送，但是当我使用 Wireshark 观察我的 Windows 机器中的传入数据包时，没有传入 ICMP 请求观察到。
我编写了以下代码来实现 ICMP 回显请求和回复。
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <netinet/ip_icmp.h>
#include <time.h>
#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <string.h>
#include <netinet/if_ether.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <sys/ioctl.h>
#define PING_PKT_S 64
#define PORT_NO 0
#define PING_SLEEP_RATE 1000000
#define RECV_TIMEOUT 1
int pingloop=1;
struct ping_pkt
{
struct ethhdr eth;
struct ip ip;
struct icmphdr hdr;
char msg[PING_PKT_S-sizeof(struct icmphdr)];
}g_pckt;
typedef struct ping_ctx{
int tos;
int ttl;
char srcIP[200];
char dstIP[200];
int r_sock;
}ping_ctx;
unsigned short checksum(void *b, int len)
{
unsigned short *buf = b;
unsigned int sum=0;
unsigned short result;
for ( sum = 0; len > 1; len -= 2 )
sum += *buf++;
if ( len == 1 )
sum += *(unsigned char*)buf;
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
result = ~sum;
return result;
}
void intHandler(int dummy)
{
pingloop=0;
}
void fill_ip_h(struct ip *ip, ping_ctx* ctx)
{
ip->ip_src.s_addr = inet_addr(ctx->srcIP);
ip->ip_dst.s_addr = inet_addr(ctx->dstIP);
ip->ip_v = 4;
ip->ip_hl = sizeof*ip >> 2;
ip->ip_tos = (unsigned char)(ctx->tos);
ip->ip_len = htons(sizeof(g_pckt)-sizeof(struct ethhdr));
ip->ip_id = htons(4321);
ip->ip_off = htons(0);
ip->ip_ttl = (unsigned char)(ctx->ttl);
ip->ip_p = 1;
ip->ip_sum = 0; /* Let kernel fills in */
}
void fill_icmp_h(struct icmphdr* hdr,int *msg_count)
{
hdr->type = ICMP_ECHO;
hdr->un.echo.id = 1;
hdr->un.echo.sequence = (*msg_count)++;
}
void fill_data(unsigned char * data)
{
memset(data, 'J', PING_PKT_S-sizeof(struct icmphdr));
}
void fill_eth(struct ethhdr* eth){
eth->h_source[0] = 0x78;
eth->h_source[1] = 0xe7;
eth->h_source[2] = 0xd1;
eth->h_source[3] = 0xe2;
eth->h_source[4] = 0xc3;
eth->h_source[5] = 0x48;
eth->h_dest[0] = 0xc0;
eth->h_dest[1] = 0x42;
eth->h_dest[2] = 0xd0;
eth->h_dest[3] = 0x6e;
eth->h_dest[4] = 0xe1;
eth->h_dest[5] = 0xd9;
eth->h_proto = htons(ETH_P_IP);
}
int recv_ping(int ping_sockfd)
{
int addr_len,msg_received_count=0,on =1;
struct sockaddr_ll r_addr;
/*struct timespec time_start, time_end, tfs, tfe;
long double rtt_msec=0, total_msec=0;
struct timeval tv_out;*/
char* buffer = (char*) malloc (65536);
/*Timer Settings*/
//tv_out.tv_sec = RECV_TIMEOUT;
//tv_out.tv_usec = 0;
//clock_gettime(CLOCK_MONOTONIC, &tfs);
addr_len=sizeof(r_addr);
memset(buffer,0,65536);
if ( recvfrom(ping_sockfd, buffer, 65536, 0,
(struct sockaddr*)&r_addr, &addr_len) <= 0 ) {
printf("\nPacket receive failed!\n");
}
else{
/*clock_gettime(CLOCK_MONOTONIC, &time_end);
double timeElapsed = ((double)(time_end.tv_nsec -
time_start.tv_nsec))/1000000.0;
rtt_msec = (time_end.tv_sec - time_start.tv_sec) * 1000.0 + timeElapsed;
msg_received_count++;*/
struct ethhdr *eth = (struct ethhdr*) (buffer);
unsigned short iphdrlen;
struct iphdr *ip = (struct iphdr*)(buffer + sizeof(struct ethhdr));
if((unsigned int)ip->protocol==1){
printf("\n Ethernet Header \n");
printf("\t|Source Address : %.2X - %.2X - %.2X - %.2X - %.2X - %.2X",eth->h_source[0],eth->h_source[1],eth->h_source[2],eth->h_source[3],eth->h_source[4],eth->h_source[5]);
printf("\t|Destination Address : %.2X - %.2X - %.2X - %.2X - %.2X - %.2X",eth->h_dest[0],eth->h_dest[1],eth->h_dest[2],eth->h_dest[3],eth->h_dest[4],eth->h_dest[5]);
printf("\n Internet header \n");
printf("\t|-Version : %d\n",(unsigned int)ip->version);
printf("\t|-Internet Header Length : %d DWORDS or %d Bytes\n",(unsigned int)ip->ihl,((unsigned int)(ip->ihl))*4);
printf("\t|-Type Of Service : %d\n",(unsigned int)ip->tos);
printf("\t|-Total Length : %d Bytes\n",ntohs(ip->tot_len));
printf("\t|-Identification : %d\n",ntohs(ip->id));
printf("\t|-Time To Live : %d\n",(unsigned int)ip->ttl);
printf("\t|-Protocol : %d\n",(unsigned int)ip->protocol);
printf("\t|-Header Checksum : %d\n",ntohs(ip->check));
printf("\t|-Source IP : %d\n", ip->saddr);
printf("\t|-Destination IP : %d\n",ip->daddr);
return 1;
}
else{
return 0;
}
}
}
void send_ping(ping_ctx* ctx,int r_sock)
{
int msg_count=0, i, addr_len, pkt_sent=1,
msg_received_count=0,on =1;
struct sockaddr_ll remote_addr;
struct ip *ip = NULL;
struct icmphdr* icmph = NULL;
unsigned char* data = NULL;
struct ethhdr* eth = NULL;
struct sockaddr_ll r_addr;
struct timespec time_start, time_end, tfs, tfe;
long double rtt_msec=0, total_msec=0;
struct timeval tv_out;
/*Set params*/
char *to = ctx->dstIP;
char *from = ctx->srcIP;
int ping_sockfd = ctx->r_sock;
int ttl = ctx->ttl;
int tos =ctx->tos;
/*Timer Settings*/
tv_out.tv_sec = RECV_TIMEOUT;
tv_out.tv_usec = 0;
//clock_gettime(CLOCK_MONOTONIC, &tfs);
//GET INTERFACE INDEX FOR INTERFACE enp0s3
/*struct ifreq ifr;
size_t if_name_len = strlen(if_name);
if(if_name_len<sizeof(ifr.ifr_name)){
memcpy(ifr.ifr_name,if_name,if_name_len);
ifr.ifr_name[if_name_len]=0;
}
else{
die("Interface name is too long");
}
memset(&ifr,0,sizeof(ifr));
strncpy(ifr.ifr_name,enp0s3,IFNAMSIZ-1);
int fd = socket(AF_UNIX,SOCK_DGRAM,0);
if(fd==-1)
printf("Error opening socket");
if(ioctl(fd,SIOCGIFINDEX,&ifr)==-1){
printf("Error getting index name");
}*/
//int ifindex = ifr.ifr_ifindex;
int ifindex = if_nametoindex("enp2s0f0");
printf("The interface number is : %d \n",ifindex);
remote_addr.sll_ifindex = ifindex;
remote_addr.sll_halen = ETH_ALEN;
remote_addr.sll_addr[0] = 0xc0;
remote_addr.sll_addr[1] = 0x42;
remote_addr.sll_addr[2] = 0xd0;
remote_addr.sll_addr[3] = 0x6e;
remote_addr.sll_addr[4] = 0xe1;
remote_addr.sll_addr[5] = 0xd9;
while(pingloop)
{
pkt_sent=1;
memset(&g_pckt, 0, sizeof(g_pckt));
/*ETHERNET Header*/
eth = (struct ethhdr *)&g_pckt;
fill_eth(eth);
/*IP Header*/
ip = (struct ip *)(eth + 1);
fill_ip_h(ip, ctx);
/*ICMP Header*/
icmph = (struct icmphdr*)(ip + 1);
fill_icmp_h(icmph, &msg_count);
/*Data*/
data = (unsigned char *)(icmph + 1);
fill_data(data);
/*ICMP Checksum*/
icmph->checksum = checksum(icmph, PING_PKT_S);
usleep(PING_SLEEP_RATE);
/*TX*/
clock_gettime(CLOCK_MONOTONIC, &time_start);
if ( sendto(ping_sockfd, &g_pckt, sizeof(g_pckt), 0,
(struct sockaddr*) &remote_addr,
sizeof(remote_addr)) <= 0)
{
printf("\nPacket Sending Failed!\n");
pkt_sent=0;
}
/*RX*/
/*addr_len=sizeof(r_addr);
if ( recvfrom(ping_sockfd, icmph, PING_PKT_S, 0,
(struct sockaddr*)&r_addr, &addr_len) <= 0
&& msg_count>1)
{
printf("\nPacket receive failed!\n");
} */
else
{
/*clock_gettime(CLOCK_MONOTONIC, &time_end);
double timeElapsed = ((double)(time_end.tv_nsec -
time_start.tv_nsec))/1000000.0;
rtt_msec = (time_end.tv_sec-
time_start.tv_sec) * 1000.0
+ timeElapsed;*/
// if packet was not sent, don't receive
if(pkt_sent)
{
msg_count++;
if(recv_ping(r_sock)){
msg_received_count++;
}
//printf("Total Messages received : %d\n", msg_received_count );
/*if(!(g_pckt.hdr.type ==69 && g_pckt.hdr.code==0))
{
printf("Error..Packet received with ICMP"
"type %d code %d\n",
g_pckt.hdr.type, g_pckt.hdr.code);
}
else
{
printf("%d bytes Received reply from %s: icmp_seq=:%d ttl=%d time=%Lf ms\n",PING_PKT_S, ctx->dstIP, msg_count, ctx->ttl, rtt_msec);
msg_received_count++;
} */
}
}
}
/*clock_gettime(CLOCK_MONOTONIC, &tfe);
double timeElapsed = ((double)(tfe.tv_nsec -
tfs.tv_nsec))/1000000.0;
total_msec = (tfe.tv_sec-tfs.tv_sec)*1000.0+
timeElapsed ;*/
printf("\n%d packets sent, %d packets received\n\n",
msg_count, msg_received_count);
}
int main(int argc, char *argv[])
{
ping_ctx ctx = {0};
if(argc!=3)
{
printf("sudo ./myping 10.117.157.6 10.39.51.117\n");
return 0;
}
signal(SIGINT, intHandler);
ctx.r_sock = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW);
int r_sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));
if(r_sock <0)
{
printf("\nSocket file descriptor not received\n");
return 0;
}
if(ctx.r_sock <0)
{
printf("%d",ctx.r_sock);
printf("\nSocket file descriptor not received\n");
return 0;
}
ctx.tos = 0;
ctx.ttl = 64;
strncpy(ctx.dstIP, argv[1],strlen(argv[1]));
strncpy(ctx.srcIP, argv[2],strlen(argv[2]));
send_ping(&ctx,r_sock);
return 0;
}
此外，调用的 sendto api return 值为 0，表示仅发送了 0 个字节，这不应该是理想情况，因为它应该 return发送的字节数应等于数据包大小。
我知道代码 posted 很长，但我不确定是哪一部分导致了错误。所以我想 post 整个代码。任何快速帮助将不胜感激。
Linux 发件人的 tcpdump 捕获如下所示
enter image description here
好的，我明白了。显然 AF_PACKET 总是假定数据包将被完全填满。完全我的意思是完全。我试图省略内核的 IPv4 校验和来填充，尽管 AF_INET 是成功的，但 AF_PACKET 不是这样。所以 AF_PACKET 必须填写校验和，这样做一切都很好。
我正在尝试使用 Raw Socket 自己实现一个 ICMP echo ping 数据包。在我的 Linux 机器上进行 tcpdump 时，我发现 Echo ping 请求已成功发送，但是当我使用 Wireshark 观察我的 Windows 机器中的传入数据包时，没有传入 ICMP 请求观察到。
我编写了以下代码来实现 ICMP 回显请求和回复。
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <netinet/ip_icmp.h>
#include <time.h>
#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <string.h>
#include <netinet/if_ether.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <sys/ioctl.h>
#define PING_PKT_S 64
#define PORT_NO 0
#define PING_SLEEP_RATE 1000000
#define RECV_TIMEOUT 1
int pingloop=1;
struct ping_pkt
{
struct ethhdr eth;
struct ip ip;
struct icmphdr hdr;
char msg[PING_PKT_S-sizeof(struct icmphdr)];
}g_pckt;
typedef struct ping_ctx{
int tos;
int ttl;
char srcIP[200];
char dstIP[200];
int r_sock;
}ping_ctx;
unsigned short checksum(void *b, int len)
{
unsigned short *buf = b;
unsigned int sum=0;
unsigned short result;
for ( sum = 0; len > 1; len -= 2 )
sum += *buf++;
if ( len == 1 )
sum += *(unsigned char*)buf;
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
result = ~sum;
return result;
}
void intHandler(int dummy)
{
pingloop=0;
}
void fill_ip_h(struct ip *ip, ping_ctx* ctx)
{
ip->ip_src.s_addr = inet_addr(ctx->srcIP);
ip->ip_dst.s_addr = inet_addr(ctx->dstIP);
ip->ip_v = 4;
ip->ip_hl = sizeof*ip >> 2;
ip->ip_tos = (unsigned char)(ctx->tos);
ip->ip_len = htons(sizeof(g_pckt)-sizeof(struct ethhdr));
ip->ip_id = htons(4321);
ip->ip_off = htons(0);
ip->ip_ttl = (unsigned char)(ctx->ttl);
ip->ip_p = 1;
ip->ip_sum = 0; /* Let kernel fills in */
}
void fill_icmp_h(struct icmphdr* hdr,int *msg_count)
{
hdr->type = ICMP_ECHO;
hdr->un.echo.id = 1;
hdr->un.echo.sequence = (*msg_count)++;
}
void fill_data(unsigned char * data)
{
memset(data, 'J', PING_PKT_S-sizeof(struct icmphdr));
}
void fill_eth(struct ethhdr* eth){
eth->h_source[0] = 0x78;
eth->h_source[1] = 0xe7;
eth->h_source[2] = 0xd1;
eth->h_source[3] = 0xe2;
eth->h_source[4] = 0xc3;
eth->h_source[5] = 0x48;
eth->h_dest[0] = 0xc0;
eth->h_dest[1] = 0x42;
eth->h_dest[2] = 0xd0;
eth->h_dest[3] = 0x6e;
eth->h_dest[4] = 0xe1;
eth->h_dest[5] = 0xd9;
eth->h_proto = htons(ETH_P_IP);
}
int recv_ping(int ping_sockfd)
{
int addr_len,msg_received_count=0,on =1;
struct sockaddr_ll r_addr;
/*struct timespec time_start, time_end, tfs, tfe;
long double rtt_msec=0, total_msec=0;
struct timeval tv_out;*/
char* buffer = (char*) malloc (65536);
/*Timer Settings*/
//tv_out.tv_sec = RECV_TIMEOUT;
//tv_out.tv_usec = 0;
//clock_gettime(CLOCK_MONOTONIC, &tfs);
addr_len=sizeof(r_addr);
memset(buffer,0,65536);
if ( recvfrom(ping_sockfd, buffer, 65536, 0,
(struct sockaddr*)&r_addr, &addr_len) <= 0 ) {
printf("\nPacket receive failed!\n");
}
else{
/*clock_gettime(CLOCK_MONOTONIC, &time_end);
double timeElapsed = ((double)(time_end.tv_nsec -
time_start.tv_nsec))/1000000.0;
rtt_msec = (time_end.tv_sec - time_start.tv_sec) * 1000.0 + timeElapsed;
msg_received_count++;*/
struct ethhdr *eth = (struct ethhdr*) (buffer);
unsigned short iphdrlen;
struct iphdr *ip = (struct iphdr*)(buffer + sizeof(struct ethhdr));
if((unsigned int)ip->protocol==1){
printf("\n Ethernet Header \n");
printf("\t|Source Address : %.2X - %.2X - %.2X - %.2X - %.2X - %.2X",eth->h_source[0],eth->h_source[1],eth->h_source[2],eth->h_source[3],eth->h_source[4],eth->h_source[5]);
printf("\t|Destination Address : %.2X - %.2X - %.2X - %.2X - %.2X - %.2X",eth->h_dest[0],eth->h_dest[1],eth->h_dest[2],eth->h_dest[3],eth->h_dest[4],eth->h_dest[5]);
printf("\n Internet header \n");
printf("\t|-Version : %d\n",(unsigned int)ip->version);
printf("\t|-Internet Header Length : %d DWORDS or %d Bytes\n",(unsigned int)ip->ihl,((unsigned int)(ip->ihl))*4);
printf("\t|-Type Of Service : %d\n",(unsigned int)ip->tos);
printf("\t|-Total Length : %d Bytes\n",ntohs(ip->tot_len));
printf("\t|-Identification : %d\n",ntohs(ip->id));
printf("\t|-Time To Live : %d\n",(unsigned int)ip->ttl);
printf("\t|-Protocol : %d\n",(unsigned int)ip->protocol);
printf("\t|-Header Checksum : %d\n",ntohs(ip->check));
printf("\t|-Source IP : %d\n", ip->saddr);
printf("\t|-Destination IP : %d\n",ip->daddr);
return 1;
}
else{
return 0;
}
}
}
void send_ping(ping_ctx* ctx,int r_sock)
{
int msg_count=0, i, addr_len, pkt_sent=1,
msg_received_count=0,on =1;
struct sockaddr_ll remote_addr;
struct ip *ip = NULL;
struct icmphdr* icmph = NULL;
unsigned char* data = NULL;
struct ethhdr* eth = NULL;
struct sockaddr_ll r_addr;
struct timespec time_start, time_end, tfs, tfe;
long double rtt_msec=0, total_msec=0;
struct timeval tv_out;
/*Set params*/
char *to = ctx->dstIP;
char *from = ctx->srcIP;
int ping_sockfd = ctx->r_sock;
int ttl = ctx->ttl;
int tos =ctx->tos;
/*Timer Settings*/
tv_out.tv_sec = RECV_TIMEOUT;
tv_out.tv_usec = 0;
//clock_gettime(CLOCK_MONOTONIC, &tfs);
//GET INTERFACE INDEX FOR INTERFACE enp0s3
/*struct ifreq ifr;
size_t if_name_len = strlen(if_name);
if(if_name_len<sizeof(ifr.ifr_name)){
memcpy(ifr.ifr_name,if_name,if_name_len);
ifr.ifr_name[if_name_len]=0;
}
else{
die("Interface name is too long");
}
memset(&ifr,0,sizeof(ifr));
strncpy(ifr.ifr_name,enp0s3,IFNAMSIZ-1);
int fd = socket(AF_UNIX,SOCK_DGRAM,0);
if(fd==-1)
printf("Error opening socket");
if(ioctl(fd,SIOCGIFINDEX,&ifr)==-1){
printf("Error getting index name");
}*/
//int ifindex = ifr.ifr_ifindex;
int ifindex = if_nametoindex("enp2s0f0");
printf("The interface number is : %d \n",ifindex);
remote_addr.sll_ifindex = ifindex;
remote_addr.sll_halen = ETH_ALEN;
remote_addr.sll_addr[0] = 0xc0;
remote_addr.sll_addr[1] = 0x42;
remote_addr.sll_addr[2] = 0xd0;
remote_addr.sll_addr[3] = 0x6e;
remote_addr.sll_addr[4] = 0xe1;
remote_addr.sll_addr[5] = 0xd9;
while(pingloop)
{
pkt_sent=1;
memset(&g_pckt, 0, sizeof(g_pckt));
/*ETHERNET Header*/
eth = (struct ethhdr *)&g_pckt;
fill_eth(eth);
/*IP Header*/
ip = (struct ip *)(eth + 1);
fill_ip_h(ip, ctx);
/*ICMP Header*/
icmph = (struct icmphdr*)(ip + 1);
fill_icmp_h(icmph, &msg_count);
/*Data*/
data = (unsigned char *)(icmph + 1);
fill_data(data);
/*ICMP Checksum*/
icmph->checksum = checksum(icmph, PING_PKT_S);
usleep(PING_SLEEP_RATE);
/*TX*/
clock_gettime(CLOCK_MONOTONIC, &time_start);
if ( sendto(ping_sockfd, &g_pckt, sizeof(g_pckt), 0,
(struct sockaddr*) &remote_addr,
sizeof(remote_addr)) <= 0)
{
printf("\nPacket Sending Failed!\n");
pkt_sent=0;
}
/*RX*/
/*addr_len=sizeof(r_addr);
if ( recvfrom(ping_sockfd, icmph, PING_PKT_S, 0,
(struct sockaddr*)&r_addr, &addr_len) <= 0
&& msg_count>1)
{
printf("\nPacket receive failed!\n");
} */
else
{
/*clock_gettime(CLOCK_MONOTONIC, &time_end);
double timeElapsed = ((double)(time_end.tv_nsec -
time_start.tv_nsec))/1000000.0;
rtt_msec = (time_end.tv_sec-
time_start.tv_sec) * 1000.0
+ timeElapsed;*/
// if packet was not sent, don't receive
if(pkt_sent)
{
msg_count++;
if(recv_ping(r_sock)){
msg_received_count++;
}
//printf("Total Messages received : %d\n", msg_received_count );
/*if(!(g_pckt.hdr.type ==69 && g_pckt.hdr.code==0))
{
printf("Error..Packet received with ICMP"
"type %d code %d\n",
g_pckt.hdr.type, g_pckt.hdr.code);
}
else
{
printf("%d bytes Received reply from %s: icmp_seq=:%d ttl=%d time=%Lf ms\n",PING_PKT_S, ctx->dstIP, msg_count, ctx->ttl, rtt_msec);
msg_received_count++;
} */
}
}
}
/*clock_gettime(CLOCK_MONOTONIC, &tfe);
double timeElapsed = ((double)(tfe.tv_nsec -
tfs.tv_nsec))/1000000.0;
total_msec = (tfe.tv_sec-tfs.tv_sec)*1000.0+
timeElapsed ;*/
printf("\n%d packets sent, %d packets received\n\n",
msg_count, msg_received_count);
}
int main(int argc, char *argv[])
{
ping_ctx ctx = {0};
if(argc!=3)
{
printf("sudo ./myping 10.117.157.6 10.39.51.117\n");
return 0;
}
signal(SIGINT, intHandler);
ctx.r_sock = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW);
int r_sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));
if(r_sock <0)
{
printf("\nSocket file descriptor not received\n");
return 0;
}
if(ctx.r_sock <0)
{
printf("%d",ctx.r_sock);
printf("\nSocket file descriptor not received\n");
return 0;
}
ctx.tos = 0;
ctx.ttl = 64;
strncpy(ctx.dstIP, argv[1],strlen(argv[1]));
strncpy(ctx.srcIP, argv[2],strlen(argv[2]));
send_ping(&ctx,r_sock);
return 0;
}
此外，调用的 sendto api return 值为 0，表示仅发送了 0 个字节，这不应该是理想情况，因为它应该 return发送的字节数应等于数据包大小。
我知道代码 posted 很长，但我不确定是哪一部分导致了错误。所以我想 post 整个代码。任何快速帮助将不胜感激。
Linux 发件人的 tcpdump 捕获如下所示
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好的，我明白了。显然 AF_PACKET 总是假定数据包将被完全填满。完全我的意思是完全。我试图省略内核的 IPv4 校验和来填充，尽管 AF_INET 是成功的，但 AF_PACKET 不是这样。所以 AF_PACKET 必须填写校验和，这样做一切都很好。