在具有有线和无线接口(例如192.168.1.x和192.168.2.x子网)的Linux系统上,我想发送UDP广播,该广播通过所有可用接口(即通过有线和无线无线接口)。
当前,我将sendto()发送到INADDR_BROADCAST,但是似乎广播只是通过其中一个接口发送的(并不总是相同的,后续广播可能会使用另一个接口)。
是否可以通过每个接口发送UDP广播?
首先,您应该考虑过时的广播,特别是INADDR_BROADCAST
(255.255.255.255)。您的问题恰恰突出了广播不适合的原因之一。它应该与IPv4一起消失(希望如此)。请注意,IPv6甚至没有广播的概念(而是使用多播)。
INADDR_BROADCAST
仅限于本地链接。如今,唯一可见的用途是用于DHCP自动配置,因为此时,客户端尚不知道客户端所连接的网络。
[使用单个sendto()
,仅生成单个数据包,并且传出接口由操作系统的路由表(在Linux上为ip route
)确定。您不能让单个sendto()
生成多个数据包,您必须遍历所有接口,并使用原始套接字或使用setsockopt(..., SOL_SOCKET, SO_BINDTODEVICE, "ethX")
将套接字绑定到设备,以绕过OS路由表发送每个数据包(这需要root特权)。这不是一个好的解决方案。
相反,由于无论如何都不会路由INADDR_BROADCAST
,因此可以通过遍历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目的。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。对这些地址中的每一个都调用一次sendto()
,您将实现目标。
[Edit:固定有关INADDR_BROADCAST
的信息,并用有关SO_BINDTODEVICE
的信息补充答案。
您不可能在每个接口上都有一个sendto()
生成一个数据包-通常(尽管有分段),每个sendto()
都是一个数据包。
您将需要为每个接口传输一次数据包,并且其中一个:
使用低级(setsockopt()
?)呼叫选择出站接口
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在与它们所用接口相同的子网中正确地配置了IP地址。重新连接。
从Jeremy's solution在UNIX套接字常见问题解答:
#include <stdio.h>
#ifdef WIN32
# include <windows.h>
# include <winsock.h>
# include <iphlpapi.h>
#else
# include <unistd.h>
# include <stdlib.h>
# include <sys/socket.h>
# include <netdb.h>
# include <netinet/in.h>
# include <net/if.h>
# include <sys/ioctl.h>
#endif
#include <string.h>
#include <sys/stat.h>
typedef unsigned long uint32;
#if defined(__FreeBSD__) || defined(BSD) || defined(__APPLE__) || defined(__linux__)
# define USE_GETIFADDRS 1
# include <ifaddrs.h>
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; i<ipTable->dwNumEntries; 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;
}
[我在github上找到了一个解决方案:https://github.com/dechamps/WinIPBroadcast。它在所有接口上发送广播,并且自述文件解释了原因。