问题描述
在UNIX上使用C，我的客户正在侦听端口68超级用户模式。发送DHCP后发现的消息，当我尝试接收，它recvfrom的块意味着没有收到任何消息或者是像系统有一个过程（DHCP客户端）监听接收邮件和多数民众赞成我的进程不能同一个端口68上接收消息。有什么问题？
我已经设置了套接字选项SO_REUSEADDR和SO_BROADCAST。我发送到端口67。
结构dhcpmessage
{
uint8_t有运;
uint8_t有HTYPE;
uint8_t有hLen的;
uint8_t有啤酒花;
uint32_t的XID;
uint16_t秒;
uint16_t标志;
uint32_t的CIADDR;
uint32_t的YIADDR;
uint32_t的的siaddr;
uint32_t的GIADDR;
焦炭CHADDR [16];
字符SNAME [64];
字符文件[128];
炭魔[4];
炭选择[3];
} __attribute __（（__ packed__））;＃包括LT＆;＆stdio.h中GT;
＃包括LT＆;＆文件ctype.h GT;
＃包括LT＆;＆stdlib.h中GT;
＃包括LT＆;＆string.h中GT;
＃包括LT＆;＆unistd.h中GT;
＃包括LT＆;＆signal.h中GT;
＃包括LT＆; SYS / wait.h＆GT;
＃包括LT＆; SYS / types.h中＆GT;
＃包括LT＆; SYS / socket.h中＆GT;
＃包括LT＆; netinet / in.h中＆GT;
＃包括LT＆; ARPA / inet.h＆GT;
＃包括LT＆;＆errno.h中GT;
＃包括LT＆; SYS / file.h＆GT;
＃包括LT＆; SYS / msg.h＆GT;
＃包括LT＆; SYS / ipc.h＆GT;
＃包括LT＆;＆time.h中GT;
的#include的defs.h
诠释主（）{
INT的sockfd，listenfd，connfd;
关于= 1 const int的;
结构SOCKADDR_IN servaddr，cliaddr，rservaddr;
如果（（的sockfd =插座（AF_INET，SOCK_DGRAM，0））小于0）
死（插座）;
如果（setsockopt的（的sockfd，SOL_SOCKET，SO_REUSEADDR，＆放大器;上，的sizeof（上））小于0）
死（setsockopt的）;如果（setsockopt的（的sockfd，SOL_SOCKET，SO_BROADCAST，＆放大器;上，的sizeof（上））小于0）
死（setsockopt的）;
bzero（安培; servaddr，sizeof的（servaddr））;
bzero（安培; cliaddr，sizeof的（cliaddr））;
cliaddr.sin_port = htons（68）;
cliaddr.sin_family = AF_INET;
cliaddr.sin_addr.s_addr = htonl（INADDR_ANY）;
如果（绑定（的sockfd，（结构sockaddr *）及cliaddr，sizeof的（cliaddr））小于0）
死（绑定）;servaddr.sin_port = htons（67）;
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = inet_addr（255.255.255.255）;
结构dhcpmessage dhcpmsg;
bzero（安培; dhcpmsg，sizeof的（dhcpmsg））;
dhcpmsg.op = 1;
dhcpmsg.htype = 1;
dhcpmsg.hlen = 6;
dhcpmsg.hops = 0;
dhcpmsg.xid = htonl（1000）;
dhcpmsg.secs = htons（0）;
dhcpmsg.flags = htons（0x8000）时;
dhcpmsg.chaddr [0] = 0×00;
dhcpmsg.chaddr [1] = 0x1A的;
dhcpmsg.chaddr [2] = 0x80的;
dhcpmsg.chaddr [3] = 0x80的;
dhcpmsg.chaddr [4] = 0x2C;
dhcpmsg.chaddr [5] = 0xC3;
dhcpmsg.magic [0] = 99;
dhcpmsg.magic [1] = 130;
dhcpmsg.magic [2] = 83;
dhcpmsg.magic [3] = 99;
dhcpmsg.opt [0] = 53;
dhcpmsg.opt [1] = 1;
dhcpmsg.opt [2] = 1;
如果（SENDTO（的sockfd，＆放大器; dhcpmsg，sizeof的（dhcpmsg），0，（结构sockaddr *）及servaddr，sizeof的（servaddr））小于0）
死（SENDTO）;
结构dhcpmessage recvdhcpmsg;
socklen_t的rservlen = sizeof的（rservaddr）;
如果（recvfrom的（的sockfd，＆放大器; recvdhcpmsg，sizeof的（recvdhcpmsg），0，（结构sockaddr *）及rservaddr，＆放大器; rservlen）℃的）
死（recvfrom的）;
字符*海峡=（字符*）及recvdhcpmsg;
INT I;
对于（i = 0; I＆LT;的sizeof（recvdhcpmsg）;我++）
的printf（％d个_，海峡[I]）;
的printf（\\ n）;
返回0;
}
需要注意的是，你没有一个IP地址，你想获得的。 - 大多数操作系统不会允许你绑定/上网卡发送UDP消息W / O的IP地址。 DHCP客户端通常使用原始套接字用于这一目的/并应设置SRC地址为0.0.0.0）
这种原始套接字将得到所有的数据包，您的应用程序不会，如果有运行的系统DHCP客户端
On unix using C, my client is listening on port 68 with superuser mode. After sending DHCP discover message, when I try to receive, it blocks in recvfrom means there is no message received or is it like system has a process (DHCP client) listening on same port 68 which receives the message and thats my process are not able to receive the message. What is the problem?
I have set the socket option SO_REUSEADDR and SO_BROADCAST. I am sending to port 67.
struct dhcpmessage
{
uint8_t op;
uint8_t htype;
uint8_t hlen;
uint8_t hops;
uint32_t xid;
uint16_t secs;
uint16_t flags;
uint32_t ciaddr;
uint32_t yiaddr;
uint32_t siaddr;
uint32_t giaddr;
char chaddr[16];
char sname[64];
char file[128];
char magic[4];
char opt[3];
} __attribute__((__packed__));
#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<signal.h>
#include<sys/wait.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
#include<sys/file.h>
#include<sys/msg.h>
#include<sys/ipc.h>
#include<time.h>
#include"defs.h"
int main() {
int sockfd,listenfd,connfd;
const int on=1;
struct sockaddr_in servaddr,cliaddr,rservaddr;
if((sockfd=socket(AF_INET,SOCK_DGRAM,0)) < 0)
die("socket");
if(setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)) < 0)
die("setsockopt");
if(setsockopt(sockfd,SOL_SOCKET,SO_BROADCAST,&on,sizeof(on)) < 0)
die("setsockopt");
bzero(&servaddr,sizeof(servaddr));
bzero(&cliaddr,sizeof(cliaddr));
cliaddr.sin_port = htons(68);
cliaddr.sin_family = AF_INET;
cliaddr.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sockfd,(struct sockaddr*)&cliaddr,sizeof(cliaddr)) < 0)
die("bind");
servaddr.sin_port = htons(67);
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = inet_addr("255.255.255.255");
struct dhcpmessage dhcpmsg;
bzero(&dhcpmsg,sizeof(dhcpmsg));
dhcpmsg.op = 1;
dhcpmsg.htype = 1;
dhcpmsg.hlen = 6;
dhcpmsg.hops = 0;
dhcpmsg.xid = htonl(1000);
dhcpmsg.secs = htons(0);
dhcpmsg.flags = htons(0x8000);
dhcpmsg.chaddr[0] = 0x00;
dhcpmsg.chaddr[1] = 0x1A;
dhcpmsg.chaddr[2] = 0x80;
dhcpmsg.chaddr[3] = 0x80;
dhcpmsg.chaddr[4] = 0x2C;
dhcpmsg.chaddr[5] = 0xC3;
dhcpmsg.magic[0]=99;
dhcpmsg.magic[1]=130;
dhcpmsg.magic[2]=83;
dhcpmsg.magic[3]=99;
dhcpmsg.opt[0]=53;
dhcpmsg.opt[1]=1;
dhcpmsg.opt[2]=1;
if(sendto(sockfd,&dhcpmsg,sizeof(dhcpmsg),0,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
die("sendto");
struct dhcpmessage recvdhcpmsg;
socklen_t rservlen = sizeof(rservaddr);
if(recvfrom(sockfd,&recvdhcpmsg,sizeof(recvdhcpmsg),0,(struct sockaddr*)&rservaddr,&rservlen) < 0)
die("recvfrom");
char *str = (char*)&recvdhcpmsg;
int i;
for(i=0;i<sizeof(recvdhcpmsg);i++)
printf("%d_",str[i]);
printf("\n");
return 0;
}
The caveat is, you don't have an IP address, you want to obtain one. - most OSs won't allow you to bind/send UDP messages on a NIC w/o an IP address. dhcp clients typically use raw sockets for that purpose/and should set the src address to 0.0.0.0)
Such a raw socket will get all the packets, and your application will not if there's a system dhcp client running
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