我发送广播包以检测dhcp服务器（255.255.255.255到端口67）已经卡住了几个星期。
如果有人可以花点时间在思考过程中发现我的缺陷，我会很感激。
我制作了一个shellcript来杀死dhcpd并断开我的Wifi并再次使用wpa_supplicant连接
echo "Killing DHCP daemon to open up port 68"
sudo killall -TERM dhcpcd dhclient
echo "Stopping Network Service"
sudo /etc/init.d/network stop
echo "Ifdown on network interfaces"
sudo /sbin/ifconfig eth0 down
sudo /sbin/ifconfig wlan0 down
echo "Connecting to Wifi using WPA_Supplicant"
sudo /usr/sbin/wpa_supplicant -Dwext -iwlan0 -c/etc/wpa_supplicant/wpa_supplicant.conf &
user@suse:sudo /usr/sbin/wpa_cli status
root's password:
Selected interface 'wlan0'
bssid=5c:35:3b:64:79:59
ssid=Joehoe
id=0
mode=station
pairwise_cipher=TKIP
group_cipher=TKIP
key_mgmt=WPA2-PSK
wpa_state=COMPLETED
address=00:26:c7:1e:a2:42
旁注：如果此时运行/ usr / sbin / dhclient工作正常，那么我得出的结论是无线真的很好
我运行以下代码：
/** Compile : gcc -m32 dhcpclient.c -o dhcpclient */
#define DHCPSERVERPORT 67
#define DHCPCLIENTPORT 68
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/******************************************************************/
/************ DHCP Message Structure ********************/
typedef struct {
unsigned char op; // Message opcode/type // unsigned char can be replaced by uint8_t, see C manual for info
unsigned char htype; // Hardware addr type
unsigned char hlen; // Hardware addr length
unsigned char hops; // Number of relay agent hops from client
unsigned long xid; // Transaction ID
unsigned short secs; // Seconds since client started looking
unsigned short flags; // Flag bits
struct in_addr ciaddr; // Client IP address (if already in use)
struct in_addr yiaddr; // Client IP address
struct in_addr siaddr; // IP address of next server to talk to
struct in_addr giaddr; // DHCP relay agent IP address
unsigned char chaddr[16]; // Client hardware address
char sname[64]; // Server name
char file[128]; // Boot filename
char magiccookie[4]; // DHCP option cookie
char options[59]; // Optional parameters (actual length dependent on MTU).
} dhcp_msg;
/************ DHCP DISCOVER ********************/
dhcp_msg dhcpdiscover(){
//struct dhcp_msg dhcpdiscover;
dhcp_msg dhcpdiscover;
dhcpdiscover.op = 1;
dhcpdiscover.htype = 1;
dhcpdiscover.hlen = 6;
dhcpdiscover.hops = 0;
dhcpdiscover.xid = 0;
dhcpdiscover.secs = 0;
dhcpdiscover.flags = 0;
dhcpdiscover.ciaddr.s_addr = htonl(INADDR_ANY);
dhcpdiscover.yiaddr.s_addr = htonl(INADDR_ANY);
dhcpdiscover.siaddr.s_addr = htonl(INADDR_ANY);
dhcpdiscover.giaddr.s_addr = htonl(INADDR_ANY);
dhcpdiscover.chaddr[0] = 0x00;
dhcpdiscover.chaddr[1] = 0x26;
dhcpdiscover.chaddr[2] = 0xC7;
dhcpdiscover.chaddr[3] = 0x1E;
dhcpdiscover.chaddr[4] = 0xA2;
dhcpdiscover.chaddr[5] = 0x42;
dhcpdiscover.chaddr[6] = 0x00;
dhcpdiscover.chaddr[7] = 0x00;
dhcpdiscover.chaddr[8] = 0x00;
dhcpdiscover.chaddr[9] = 0x00;
dhcpdiscover.chaddr[10] = 0x00;
dhcpdiscover.chaddr[11] = 0x00;
dhcpdiscover.chaddr[12] = 0x00;
dhcpdiscover.chaddr[13] = 0x00;
dhcpdiscover.chaddr[14] = 0x00;
dhcpdiscover.chaddr[15] = 0x00;
memset(dhcpdiscover.sname,0,sizeof(dhcpdiscover.sname));
memset(dhcpdiscover.file,0,sizeof(dhcpdiscover.file));
/************ setting magiccookie and options to 0 -> recognized as BootP protocol ***/
dhcpdiscover.magiccookie[0] = 99;
dhcpdiscover.magiccookie[1] = 130;
dhcpdiscover.magiccookie[2] = 83;
dhcpdiscover.magiccookie[3] = 99;
dhcpdiscover.options[0] = 53;
dhcpdiscover.options[1] = 1;
dhcpdiscover.options[2] = 1;
dhcpdiscover.options[3] = 255;
/** always set 0xff as DHCP End option to close option listing, rest is padding **/
return dhcpdiscover;
}
void printDHCPStructure(dhcp_msg dhcpstructure){
dhcp_msg dhcpstruct = dhcpstructure;
printf("\n\tDHCP Field\tBytes\tValue\n");
printf("\t----------------------------------\n");
printf("\top : \t\t1\t%x\n", dhcpstruct.op);
printf("\thtype : \t1\t%x\n", dhcpstruct.htype);
printf("\thlen : \t\t1\t%x\n", dhcpstruct.hlen);
printf("\thops : \t\t1\t%x\n", dhcpstruct.hops);
printf("\txid : \t\t1\t%x\n", dhcpstruct.xid);
printf("\tsecs : \t\t1\t%x\n", dhcpstruct.secs);
printf("\tflags : \t1\t%x\n", dhcpstruct.flags);
printf("\tciaddr : \t1\t%s\n", dhcpstruct.ciaddr);
printf("\tyiaddr : \t1\t%s\n", dhcpstruct.yiaddr);
printf("\tsiaddr : \t1\t%s\n", dhcpstruct.siaddr);
printf("\tgiaddr : \t1\t%s\n", dhcpstruct.giaddr);
printf("\tchadddr[MAC] : \t16\t%x:%x:%x:%x:%x:%x\n", dhcpstruct.chaddr[0],dhcpstruct.chaddr[1],dhcpstruct.chaddr[2],dhcpstruct.chaddr[3],dhcpstruct.chaddr[4],dhcpstruct.chaddr[5]);
printf("\tsname : \t64\t%s\n", dhcpstruct.sname);
printf("\tfile : \t\t128\t%s\n", dhcpstruct.file);
printf("\tmgckie_0 : \t1\t%d\n", (unsigned char)dhcpstruct.magiccookie[0]);
printf("\tmgckie_1 : \t1\t%d\n", (unsigned char)dhcpstruct.magiccookie[1]);
printf("\tmgckie_2 : \t1\t%d\n", (unsigned char)dhcpstruct.magiccookie[2]);
printf("\tmgckie_3 : \t1\t%d\n", (unsigned char)dhcpstruct.magiccookie[3]);
printf("\toptions : \t59\t\n");
printf("\n");
}
int bindBroadcastUdpv4(int socket,short int socketport)
{
int clientsock = socket;
struct sockaddr_in udpaddr;
memset((char *)&udpaddr, 0, sizeof(udpaddr));
udpaddr.sin_family = AF_INET;
udpaddr.sin_addr.s_addr = htonl(INADDR_ANY);
udpaddr.sin_port = htons(socketport);
if (bind(clientsock, (struct sockaddr *)&udpaddr, sizeof(udpaddr)) < 0)
{
printf("Binding the UDP Socket failed\n");
printf("Tip 1 : Run 'sudo netstat -l -u -n -p | grep %d'\n", socketport);
printf("Tip 2 : Run program with root privileges\n");
perror("Error");
exit(1);
}
else
{
return 1;
}
}
/******************************************************************/
/******************************************************************/
int main(int argc, char *argv[])
{
/** Creating UDP client socket **/
int clientsock = socket(AF_INET, SOCK_DGRAM, 0);
int broadcastpermissions = 1;
short int clientport = DHCPCLIENTPORT;
short int destinationport = DHCPSERVERPORT;
if (clientsock < 0)
{
perror("Error @ Step 1 : Cannot create client socket");
}
else
{
printf("Step 1 : Client socket created succesfully\n");
}
/** Give client socket broadcast permissions **/
if (broadcastpermissions)
{
int ret = setsockopt(clientsock,SOL_SOCKET,SO_REUSEADDR,&broadcastpermissions,sizeof(broadcastpermissions));
if (ret != 0)
{
printf("Error @ step 1BisA : Giving Client Socket reuse options FAILED: %d\n", ret);
exit(0);
}
ret = setsockopt(clientsock,SOL_SOCKET,SO_BROADCAST,&broadcastpermissions,sizeof(broadcastpermissions));
if (ret != 0)
{
printf("Error @ step 1BisB : Giving Client Socket broadcast permissions FAILED: %d\n", ret);
exit(0);
}
else
{
printf("\tSetting broadcast permissions on client socket succeeded\n");
}
}
/** Binding the client socket **/
if (bindBroadcastUdpv4(clientsock, clientport))
{
printf("Step 2 : Socket is binded succesfully\n");
}
/** Create DHCP Discovery data structure **/
dhcp_msg dhcpdiscovery = dhcpdiscover();
printf("Step 3 : DHCP Discovery Data Structure created\n");
printDHCPStructure(dhcpdiscovery);
/** Trying to broadcast to 255.255.255.255 on port 67 to detect DHCP Servers */
struct sockaddr_in destinationaddr;
memset((char *)&destinationaddr, 0, sizeof(destinationaddr));
destinationaddr.sin_family = AF_INET;
//destinationaddr.sin_addr.s_addr = INADDR_BROADCAST;
destinationaddr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
destinationaddr.sin_port = htons(destinationport);
//destinationaddr.sin_port = destinationport;
/** translate Hexadecimal notation of IP Address to decimal **/
int IP1 = (ntohl(destinationaddr.sin_addr.s_addr) >> 24) & 0xFF;
int IP2 = (ntohl(destinationaddr.sin_addr.s_addr) >> 16) & 0xFF;
int IP3 = (ntohl(destinationaddr.sin_addr.s_addr) >> 8) & 0xFF;
int IP4 = (ntohl(destinationaddr.sin_addr.s_addr)) & 0xFF;
//while(1){};
printf("DEBUG : Clientsock = %d\n", clientsock);
printf("DEBUG : .sin_addr = %p\n", destinationaddr.sin_addr.s_addr);
printf("DEBUG : .sin_port = %d\n", destinationaddr.sin_port);
printf("DEBUG : .sin_port = %d\n", destinationport);
/******************************************************************************************************************************************************************/
int a = sendto(clientsock,&dhcpdiscovery,sizeof(dhcpdiscovery),0,(struct sockaddr *)&destinationaddr, sizeof(destinationaddr));
if (a < 0)
{
printf("A is :\%d\n", a);
printf("UDP Message to %d.%d.%d.%d on port %d failed\n",IP1,IP2,IP3,IP4,destinationport);
perror("Sending failed : ");
return 667;
}
else
{
printf("UDP Messsage to %d.%d.%d.%d on port %d SUCCESS !\n",IP1,IP2,IP3,IP4,destinationport);
}
close(clientsock);
}
/******************************************************************/
/******************************************************************/
额外信息： A）如前所述，当运行dhclient时，我得到ip地址分配，wiresharks显示我dhcp对话
B）当已经分配了ipaddress时运行我自己的代码时，发送成功
C）sendTo返回的错误是“网络无法访问”
所以我的问题是：我连接到我的无线AP，我需要执行额外的步骤，以便我可以让我的套接字发送广播数据包？ 这样做的原因是要了解网络并学习编程，所以我的编程技巧并不令人敬畏，这就是为什么你可能会看到荒谬的代码。我很感激任何评论，但更愿意坚持我的主要问题。
最诚挚的问候地球人！
答案 0 :(得分：0)
我认为你做想在这里使用原始套接字。虽然它是真的（根据@cklin）这意味着你必须稍微重新发明轮子，dhcp是不寻常的，因为你在正确配置接口之前发送数据包。作为一个简单的指南，我建议你看看busybox以及它的dhclient脚本是如何工作的。另一种选择是libpcap。这可以捕获回复（甚至不是直接发给你的回复），并且具有一些鲜为人知的能够发送原始数据包的功能。我已成功使用它来编写dhcp服务器。