所有接口上的UDP广播

在具有有线和无线接口的Linux系统(例如192.168.1.x和192.168.2.x子网)上,我想发送通过所有可用接口发出的UDP广播(即通过有线和无线接口发送) ).

目前我发送到()到INADDR_BROADCAST,但似乎广播只通过其中一个接口发送(并不总是相同,后续广播可能使用其他接口).

有没有办法可以发送通过每个接口发出的UDP广播？

1> Juliano..：

---

首先,你应该考虑广播过时,特别是INADDR_BROADCAST(255.255.255.255).您的问题突出了广播不适合的原因之一.它应该与IPv4一起消亡(希望如此).请注意,IPv6甚至没有广播的概念(使用多播).

INADDR_BROADCAST仅限于本地链接.如今,它只是可见的用于DHCP自动配置,因为在这个时候,客户端将不知道它连接到什么网络.

使用sendto()单个数据包,只生成一个数据包,并且输出接口由操作系统的路由表(ip route在Linux上)确定.您不能sendto()生成多个数据包,您必须迭代所有接口,并使用原始套接字或将套接字绑定到设备,使用setsockopt(..., SOL_SOCKET, SO_BINDTODEVICE, "ethX")绕过OS路由表发送每个数据包(这需要root权限) .不是一个好的解决方案

相反,既然INADDR_BROADCAST没有路由,你可以通过迭代每个接口,并将数据包发送到其广播地址来实现几乎相同的事情.例如,假设您的网络具有255.255.255.0(/ 24)掩码,则广播地址为192.168.1.255和192.168.2.255.sendto()为每个地址拨打一次电话,您就可以完成目标了.

---

编辑:修复有关信息的信息INADDR_BROADCAST,并用有关信息补充答案SO_BINDTODEVICE.

---

@Juliano不应该设置`setsockopt(...,SOL_SOCKET,SO_BROADCAST,&variable_with_one)`以便`sendto()`广播地址？如果我尝试没有设置选项,我收到一个权限被拒绝错误消息.

2> Alnitak..：

---

您不可能sendto()在每个接口上都有一个生成数据包-通常（尽管有碎片）它是每个接口传输的一个数据包sendto()。

您需要为每个接口传输一次数据包，或者：

使用低级（setsockopt()？）调用选择出站接口

发送到每个已知接口的特定广播地址

但是，如果您尝试执行某种发现机制，则后者不适合，这样您期望响应的设备实际上并未正确地用与其连接的接口相同的子网中的IP地址进行配置至。

3> 小智..：

---

来自Jeremy在UNIX Socket FAQ上的解决方案:

#include 

#ifdef WIN32
# include 
# include 
# include 
#else
# include 
# include 
# include 
# include 
# include 
# include 
# include 
#endif

#include 
#include 

typedef unsigned long uint32;

#if defined(__FreeBSD__) || defined(BSD) || defined(__APPLE__) || defined(__linux__)
# define USE_GETIFADDRS 1
# include 
static uint32 SockAddrToUint32(struct sockaddr * a)
{
   return ((a)&&(a->sa_family == AF_INET)) ? ntohl(((struct sockaddr_in *)a)->sin_addr.s_addr) : 0;
}
#endif

// convert a numeric IP address into its string representation
static void Inet_NtoA(uint32 addr, char * ipbuf)
{
   sprintf(ipbuf, "%li.%li.%li.%li", (addr>>24)&0xFF, (addr>>16)&0xFF, (addr>>8)&0xFF, (addr>>0)&0xFF);
}

// convert a string represenation of an IP address into its numeric equivalent
static uint32 Inet_AtoN(const char * buf)
{
   // net_server inexplicably doesn't have this function; so I'll just fake it
   uint32 ret = 0;
   int shift = 24;  // fill out the MSB first
   bool startQuad = true;
   while((shift >= 0)&&(*buf))
   {
      if (startQuad)
      {
         unsigned char quad = (unsigned char) atoi(buf);
         ret |= (((uint32)quad) << shift);
         shift -= 8;
      }
      startQuad = (*buf == '.');
      buf++;
   }
   return ret;
}

static void PrintNetworkInterfaceInfos()
{
#if defined(USE_GETIFADDRS)
   // BSD-style implementation
   struct ifaddrs * ifap;
   if (getifaddrs(&ifap) == 0)
   {
      struct ifaddrs * p = ifap;
      while(p)
      {
         uint32 ifaAddr  = SockAddrToUint32(p->ifa_addr);
         uint32 maskAddr = SockAddrToUint32(p->ifa_netmask);
         uint32 dstAddr  = SockAddrToUint32(p->ifa_dstaddr);
         if (ifaAddr > 0)
         {
            char ifaAddrStr[32];  Inet_NtoA(ifaAddr,  ifaAddrStr);
            char maskAddrStr[32]; Inet_NtoA(maskAddr, maskAddrStr);
            char dstAddrStr[32];  Inet_NtoA(dstAddr,  dstAddrStr);
            printf("  Found interface:  name=[%s] desc=[%s] address=[%s] netmask=[%s] broadcastAddr=[%s]\n", p->ifa_name, "unavailable", ifaAddrStr, maskAddrStr, dstAddrStr);
         }
         p = p->ifa_next;
      }
      freeifaddrs(ifap);
   }
#elif defined(WIN32)
   // Windows XP style implementation

   // Adapted from example code at http://msdn2.microsoft.com/en-us/library/aa365917.aspx
   // Now get Windows' IPv4 addresses table.  Once again, we gotta call GetIpAddrTable()
   // multiple times in order to deal with potential race conditions properly.
   MIB_IPADDRTABLE * ipTable = NULL;
   {
      ULONG bufLen = 0;
      for (int i=0; i<5; i++)
      {
         DWORD ipRet = GetIpAddrTable(ipTable, &bufLen, false);
         if (ipRet == ERROR_INSUFFICIENT_BUFFER)
         {
            free(ipTable);  // in case we had previously allocated it
            ipTable = (MIB_IPADDRTABLE *) malloc(bufLen);
         }
         else if (ipRet == NO_ERROR) break;
         else
         {
            free(ipTable);
            ipTable = NULL;
            break;
         }
     }
   }

   if (ipTable)
   {
      // Try to get the Adapters-info table, so we can given useful names to the IP
      // addresses we are returning.  Gotta call GetAdaptersInfo() up to 5 times to handle
      // the potential race condition between the size-query call and the get-data call.
      // I love a well-designed API :^P
      IP_ADAPTER_INFO * pAdapterInfo = NULL;
      {
         ULONG bufLen = 0;
         for (int i=0; i<5; i++)
         {
            DWORD apRet = GetAdaptersInfo(pAdapterInfo, &bufLen);
            if (apRet == ERROR_BUFFER_OVERFLOW)
            {
               free(pAdapterInfo);  // in case we had previously allocated it
               pAdapterInfo = (IP_ADAPTER_INFO *) malloc(bufLen);
            }
            else if (apRet == ERROR_SUCCESS) break;
            else
            {
               free(pAdapterInfo);
               pAdapterInfo = NULL;
               break;
            }
         }
      }

      for (DWORD i=0; idwNumEntries; i++)
      {
         const MIB_IPADDRROW & row = ipTable->table[i];

         // Now lookup the appropriate adaptor-name in the pAdaptorInfos, if we can find it
         const char * name = NULL;
         const char * desc = NULL;
         if (pAdapterInfo)
         {
            IP_ADAPTER_INFO * next = pAdapterInfo;
            while((next)&&(name==NULL))
            {
               IP_ADDR_STRING * ipAddr = &next->IpAddressList;
               while(ipAddr)
               {
                  if (Inet_AtoN(ipAddr->IpAddress.String) == ntohl(row.dwAddr))
                  {
                     name = next->AdapterName;
                     desc = next->Description;
                     break;
                  }
                  ipAddr = ipAddr->Next;
               }
               next = next->Next;
            }
         }
         char buf[128];
         if (name == NULL)
         {
            sprintf(buf, "unnamed-%i", i);
            name = buf;
         }

         uint32 ipAddr  = ntohl(row.dwAddr);
         uint32 netmask = ntohl(row.dwMask);
         uint32 baddr   = ipAddr & netmask;
         if (row.dwBCastAddr) baddr |= ~netmask;

         char ifaAddrStr[32];  Inet_NtoA(ipAddr,  ifaAddrStr);
         char maskAddrStr[32]; Inet_NtoA(netmask, maskAddrStr);
         char dstAddrStr[32];  Inet_NtoA(baddr,   dstAddrStr);
         printf("  Found interface:  name=[%s] desc=[%s] address=[%s] netmask=[%s] broadcastAddr=[%s]\n", name, desc?desc:"unavailable", ifaAddrStr, maskAddrStr, dstAddrStr);
      }

      free(pAdapterInfo);
      free(ipTable);
   }
#else
   // Dunno what we're running on here!
#  error "Don't know how to implement PrintNetworkInterfaceInfos() on this OS!"
#endif
}

int main(int, char **)
{
   PrintNetworkInterfaceInfos();
   return 0;
}