题
在具有有线和无线接口的 Linux 系统上(例如192.168.1.x 和 192.168.2.x 子网)我想发送通过所有可用接口(即通过有线和无线接口)。
目前我 sendto() 到 INADDR_BROADCAST,但是似乎广播仅通过其中一个接口发送(并不总是相同,后续广播可能使用另一个接口)。
有没有一种方法可以发送通过每个接口发出的 UDP 广播?
解决方案
首先,你应该考虑播出过时,特别是INADDR_BROADCAST
(255.255.255.255)。你的问题恰好凸显的原因之一是广播是不合适的。它应与IPv4的(希望)一起死。需要注意的是IPv6的甚至没有广播的概念(多播被用来代替)。
INADDR_BROADCAST
仅限于本地链路。如今,它是唯一可见的使用是通过DHCP自动配置,因为在这样的时间,客户端将不知道但在什么样的网络它连接到。
通过单个sendto()
,仅生成单个分组,并且显示出接口由操作系统的路由表(在Linux ip route
)测定。你不能有一个sendto()
生成多个数据包,你将不得不遍历所有的接口,并且或者使用原始套接字或使用setsockopt(..., SOL_SOCKET, SO_BINDTODEVICE, "ethX")
发送每个数据包绕过操作系统路由表中的套接字绑定到一个设备(这需要root权限)。不是一个很好的解决方案。
相反,因为INADDR_BROADCAST
无论如何都不会路由,您可以通过遍历每个接口,并发送数据包到广播地址实现几乎同样的事情。例如,假设你的网络具有255.255.255.0(/ 24)的掩模,该广播地址的 192.168.1.255 和<强> 192.168.2.255 即可。呼叫sendto()
一次这些地址,你会已经完成了自己的目标。
修改强>固定信息关于到INADDR_BROADCAST
,和补充用约SO_BINDTODEVICE
信息的回答
其他提示
你不能有一个 sendto()
在每个接口上生成一个数据包 - 一般来说(尽管有碎片),每个接口传输一个数据包 sendto()
.
您需要为每个接口传输一次数据包,并且:
使用低级(
setsockopt()
?) 调用选择出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配置与它们所连接的接口位于同一子网中的 IP 地址到。
#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;
}