C 如果事先没有ping,UDP数据包不会到达
我有一个代码将UDP数据包从linux设备(服务器)发送到另一个(客户端)。我有一个问题,什么时候做这件事C 如果事先没有ping,UDP数据包不会到达,c,linux,udp,ipv6,C,Linux,Udp,Ipv6,我有一个代码将UDP数据包从linux设备(服务器)发送到另一个(客户端)。我有一个问题,什么时候做这件事 重新启动服务器 运行程序发送数据包,但客户端未收到该数据包 然后,如果我对客户端ip进行ping,并再次运行该程序,那么现在该数据包将被客户端接收 代码如下: int main (int argc, char **argv){ int i, status, datalen, frame_length, sd, bytes; char *interface, *target, *
int main (int argc, char **argv){
int i, status, datalen, frame_length, sd, bytes;
char *interface, *target, *src_ip, *dst_ip;
struct ip6_hdr iphdr;
struct udphdr udphdr;
uint8_t *data, *src_mac, *dst_mac, *ether_frame;
struct addrinfo hints, *res;
struct sockaddr_in6 *ipv6;
struct sockaddr_ll device;
struct ifreq ifr;
void *tmp;
// Allocate memory for various arrays.
src_mac = allocate_ustrmem (6);
dst_mac = allocate_ustrmem (6);
data = allocate_ustrmem (IP_MAXPACKET);
ether_frame = allocate_ustrmem (IP_MAXPACKET);
interface = allocate_strmem (INET6_ADDRSTRLEN);
target = allocate_strmem (INET6_ADDRSTRLEN);
src_ip = allocate_strmem (INET6_ADDRSTRLEN);
dst_ip = allocate_strmem (INET6_ADDRSTRLEN);
// Interface to send packet through.
strcpy (interface, "usb0");
// Submit request for a socket descriptor to look up interface.
if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
perror ("socket() failed to get socket descriptor for using ioctl() ");
exit (EXIT_FAILURE);
}
// Use ioctl() to look up interface name and get its MAC address.
memset (&ifr, 0, sizeof (ifr));
snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
if (ioctl (sd, SIOCGIFHWADDR, &ifr) < 0) {
perror ("ioctl() failed to get source MAC address ");
return (EXIT_FAILURE);
}
close (sd);
// Copy source MAC address.
memcpy (src_mac, ifr.ifr_hwaddr.sa_data, 6 * sizeof (uint8_t));
// Report source MAC address to stdout.
printf ("MAC address for interface %s is ", interface);
for (i=0; i<5; i++) {
printf ("%02x:", src_mac[i]);
}
printf ("%02x\n", src_mac[5]);
// Find interface index from interface name and store index in
// struct sockaddr_ll device, which will be used as an argument of sendto().
memset (&device, 0, sizeof (device));
if ((device.sll_ifindex = if_nametoindex (interface)) == 0) {
perror ("if_nametoindex() failed to obtain interface index ");
exit (EXIT_FAILURE);
}
printf ("Index for interface %s is %i\n", interface, device.sll_ifindex);
// Set destination MAC address
dst_mac[0] = 0x00;
dst_mac[1] = 0x11;
dst_mac[2] = 0x7d;
dst_mac[3] = 0x30;
dst_mac[4] = 0x7f;
dst_mac[5] = 0xd0;
// Source IPv6 address
strcpy (src_ip, "fe80::11:7dff:fe30:8013");
// Destination URL or IPv6 address
strcpy (target, "fe80:0000:0000:0000:0211:7d00:0030:7fd0");
// Fill out hints for getaddrinfo().
memset (&hints, 0, sizeof (hints));
hints.ai_family = AF_INET6;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = hints.ai_flags | AI_CANONNAME;
// Resolve target using getaddrinfo().
if ((status = getaddrinfo (target, NULL, &hints, &res)) != 0) {
fprintf (stderr, "getaddrinfo() failed: %s\n", gai_strerror (status));
exit (EXIT_FAILURE);
}
ipv6 = (struct sockaddr_in6 *) res->ai_addr;
tmp = &(ipv6->sin6_addr);
if (inet_ntop (AF_INET6, tmp, dst_ip, INET6_ADDRSTRLEN) == NULL) {
status = errno;
fprintf (stderr, "inet_ntop() failed.\nError message: %s", strerror (status));
exit (EXIT_FAILURE);
}
freeaddrinfo (res);
// Fill out sockaddr_ll.
device.sll_family = AF_PACKET;
memcpy (device.sll_addr, src_mac, 6 * sizeof (uint8_t));
device.sll_halen = 6;
// UDP data
datalen = 4;
data[0] = 'T';
data[1] = 'E';
data[2] = 'S';
data[3] = 'T';
// IPv6 header
// IPv6 version (4 bits), Traffic class (8 bits), Flow label (20 bits)
iphdr.ip6_flow = htonl ((6 << 28) | (0 << 20) | 0);
// Payload length (16 bits): UDP header + UDP data
iphdr.ip6_plen = htons (UDP_HDRLEN + datalen);
// Next header (8 bits): 17 for UDP
iphdr.ip6_nxt = IPPROTO_UDP;
// Hop limit (8 bits): default to maximum value
iphdr.ip6_hops = 255;
// Source IPv6 address (128 bits)
if ((status = inet_pton (AF_INET6, src_ip, &(iphdr.ip6_src))) != 1) {
fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
exit (EXIT_FAILURE);
}
// Destination IPv6 address (128 bits)
if ((status = inet_pton (AF_INET6, dst_ip, &(iphdr.ip6_dst))) != 1) {
fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
exit (EXIT_FAILURE);
}
// UDP header
// Source port number (16 bits): pick a number
udphdr.source = htons (61616);
// Destination port number (16 bits): pick a number
udphdr.dest = htons (61616);
// Length of UDP datagram (16 bits): UDP header + UDP data
udphdr.len = htons (UDP_HDRLEN + datalen);
// UDP checksum (16 bits)
udphdr.check = udp6_checksum (iphdr, udphdr, data, datalen);
// Fill out ethernet frame header.
// Ethernet frame length = ethernet header (MAC + MAC + ethernet type) + ethernet data (IP header + UDP header + UDP data)
frame_length = 6 + 6 + 2 + IP6_HDRLEN + UDP_HDRLEN + datalen;
// Destination and Source MAC addresses
memcpy (ether_frame, dst_mac, 6 * sizeof (uint8_t));
memcpy (ether_frame + 6, src_mac, 6 * sizeof (uint8_t));
// Next is ethernet type code (ETH_P_IPV6 for IPv6).
// http://www.iana.org/assignments/ethernet-numbers
ether_frame[12] = ETH_P_IPV6 / 256;
ether_frame[13] = ETH_P_IPV6 % 256;
// Next is ethernet frame data (IPv6 header + UDP header + UDP data).
// IPv6 header
memcpy (ether_frame + ETH_HDRLEN, &iphdr, IP6_HDRLEN * sizeof (uint8_t));
// UDP header
memcpy (ether_frame + ETH_HDRLEN + IP6_HDRLEN, &udphdr, UDP_HDRLEN * sizeof (uint8_t));
// UDP data
memcpy (ether_frame + ETH_HDRLEN + IP6_HDRLEN + UDP_HDRLEN, data, datalen * sizeof (uint8_t));
// Submit request for a raw socket descriptor.
if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
perror ("socket() failed ");
exit (EXIT_FAILURE);
}
// Send ethernet frame to socket.
if ((bytes = sendto (sd, ether_frame, frame_length, 0, (struct sockaddr *) &device, sizeof (device))) <= 0) {
perror ("sendto() failed");
exit (EXIT_FAILURE);
}
// Close socket descriptor.
close (sd);
// Free allocated memory.
free (src_mac);
free (dst_mac);
free (data);
free (ether_frame);
free (interface);
free (target);
free (src_ip);
free (dst_ip);
return (EXIT_SUCCESS);
}
int main(int argc,char**argv){
int i,状态,数据长度,帧长度,sd,字节;
字符*接口、*目标、*src_ip、*dst_ip;
结构ip6_hdr iphdr;
结构udphdr udphdr;
uint8_t*数据、*src_mac、*dst_mac、*以太帧;
结构addrinfo提示,*res;
6*ipv6中的结构sockaddr_;
结构sockaddr\u ll设备;
结构ifreq-ifr;
无效*tmp;
//为各种阵列分配内存。
src_mac=allocate_ustrem(6);
dst_mac=分配(6);
数据=分配USTMEM(IP最大数据包);
以太帧=分配USTMEM(IP最大数据包);
接口=分配\u strem(INET6\u ADDRSTRLEN);
目标=分配\u strem(INET6\u ADDRSTRLEN);
src\u ip=分配\u strem(INET6\u ADDRSTRLEN);
dst_ip=allocate_strem(INET6_ADDRSTRLEN);
//用于发送数据包的接口。
strcpy(接口,“usb0”);
//提交套接字描述符的请求以查找接口。
如果((sd=套接字(PF_数据包、SOCK_原始、htons(ETH_P_全部)))<0){
perror(“socket()无法获取用于使用ioctl()的套接字描述符”);
退出(退出失败);
}
//使用ioctl()查找接口名称并获取其MAC地址。
memset(&ifr,0,sizeof(ifr));
snprintf(ifr.ifr\u名称,sizeof(ifr.ifr\u名称),“%s”,接口);
如果(ioctl(sd、SIOCGIFHWADDR和ifr)<0){
perror(“ioctl()无法获取源MAC地址”);
返回(退出失败);
}
关闭(sd);
//复制源MAC地址。
memcpy(src_mac,ifr.ifr_hwaddr.sa_数据,6*sizeof(uint8_t));
//向标准输出报告源MAC地址。
printf(“接口%s的MAC地址为”,接口);
对于(i=0;iai_addr;
tmp=&(ipv6->sin6地址);
if(inet_ntop(AF_INET6、tmp、dst_ip、INET6_ADDRSTRLEN)==NULL){
状态=错误号;
fprintf(stderr,“inet_ntop()失败。\n错误消息:%s”,strerror(status));
退出(退出失败);
}
freeaddrinfo(res);
//填写sockaddr\u ll。
device.sll_family=AF_数据包;
memcpy(device.sll_addr,src_mac,6*sizeof(uint8_t));
device.sll_halen=6;
//UDP数据
datalen=4;
数据[0]=“T”;
数据[1]=“E”;
数据[2]=“S”;
数据[3]=‘T’;
//IPv6报头
//IPv6版本(4位)、流量类别(8位)、流量标签(20位)
iphdr.ip6_flow=htonl((6如果dst mac
不在ARP
表中,您选择发送UDP
数据包的方法似乎会失败。不知何故,这样做会导致dst mac
的内核不ARP
(可能是因为您已手动将其插入数据包)-但是-数据包传输仍然失败,因为它不存在于ARP
表中。ping
导致ARP
表被填充,然后它开始工作
这只是一个理论。我们必须看看内核路径来证实这一点
你可以尝试几个实验来证实这个理论
不要ping
。运行该程序几次,看看它在后续运行中是否有效
首先ping
,然后尝试该程序(应该可以运行),然后刷新ARP
表,再次尝试该程序(应该失败)。使用sudo ip-s-s neigh flush all
刷新ARP
表
是否有任何理由不使用SOCK_DGRAM
,这是执行UDP
的标准方法
编辑
正如评论中所指出的,我忽略了OP正在使用IPV6的事实。将所有提到的ARP替换为邻居(以及同等的).如果你多次运行程序,没有ping或任何其他网络通信,会发生什么?如果你在运行程序之前只等待五分钟会发生什么?实际上,IPv6没有ARP-它使用NDP。没错。我没有注意到。但是理论仍然适用。是的,它有,这就是为什么我投+1票。我只是想是的您可能想更正IPv6的答案。谢谢。添加了一些词。NDP是ARP的一大改进,因为ARP广播并中断每台主机,但NDP基于IPv6地址的最后24位多播到特定组,可能只命中它试图解析第2层地址的一台主机。