这个为什么是广播包？

nait · 发表于 2005-6-19 11:54:48

下面是mystar中的一个函数

int SendFindServerPacket(libnet_t *l)
{
static uint8_t broadPackage[0x3E8] = { //广播包，用于寻找服务器
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x88,0x
8E,0x01,0x01,
0x00,0x00,0xFF,0xFF,0x37,0x77,0xFF,0x00,0x00,0x00,0x00,0x00,0x00,0x
00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x08,0x15,0x00,0x00,0x13,0x11,0x
38,0x30,0x32,
0x31,0x78,0x2E,0x65,0x78,0x65,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x
00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x
02,0x1F,0x00,
0x00,0x00,0x00,0x00,0x13,0x11,0x00,0x28,0x1A,0x28,0x00,0x00,0x13,0x
11,0x17,0x22,
0x92,0x68,0x64,0x66,0x92,0x94,0x62,0x66,0x91,0x93,0x95,0x62,0x93,0x
93,0x91,0x94,
0x64,0x61,0x64,0x64,0x65,0x66,0x68,0x94,0x98,0xA7,0x61,0x67,0x65,0x
67,0x9C,0x6B};
uint8_t StandardAddr[] = {0x01,0x80,0xC2,0x00,0x00,0x03};
uint8_t StarAddr[] = {0x01,0xD0,0xF8,0x00,0x00,0x03};
extern uint8_t m_localMAC[6];
extern int m_authenticationMode;
if (m_authenticationMode==1) memcpy(broadPackage,StarAddr,6);
else memcpy( broadPackage, StandardAddr, 6 );
memcpy( broadPackage+6, m_localMAC, 6 ); //填充MAC地址
FillNetParamater( &broadPackage[0x17] );
fputs(">>searching for server...\n",stdout);
return (libnet_write_link(l,broadPackage, 0x3E8)==0x3E8)?0:-1;
}

复制代码

注释说的很清楚，这是用来寻找服务器的广播包。
显然这应该是数据链路层的帧，按照帧的格式，前6字节是目的mac，按照我的理解，目的
mac全1才是广播啊，在本函数中，不管m_authenticationMode是什么，目的mac都不会是全
1啊，为什么是广播呢？
望大侠赐教
thx

macarthor · 发表于 2005-6-19 19:22:47

看看关于MAC的SPEC？

Illidan · 发表于 2005-6-19 21:40:21

Post by nait
下面是mystar中的一个函数

int SendFindServerPacket(libnet_t *l)

{

static uint8_t broadPackage[0x3E8] = {       //广播包，用于寻找服务器

         0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x88,0x

8E,0x01,0x01,

         0x00,0x00,0xFF,0xFF,0x37,0x77,0xFF,0x00,0x00,0x00,0x00,0x00,0x00,0x

00,0x00,0x00,

         0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x08,0x15,0x00,0x00,0x13,0x11,0x

38,0x30,0x32,

         0x31,0x78,0x2E,0x65,0x78,0x65,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x

00,0x00,0x00,

         0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x

02,0x1F,0x00,

         0x00,0x00,0x00,0x00,0x13,0x11,0x00,0x28,0x1A,0x28,0x00,0x00,0x13,0x

11,0x17,0x22,

         0x92,0x68,0x64,0x66,0x92,0x94,0x62,0x66,0x91,0x93,0x95,0x62,0x93,0x

93,0x91,0x94,

         0x64,0x61,0x64,0x64,0x65,0x66,0x68,0x94,0x98,0xA7,0x61,0x67,0x65,0x

67,0x9C,0x6B};



uint8_t StandardAddr[] = {0x01,0x80,0xC2,0x00,0x00,0x03};

uint8_t StarAddr[]    = {0x01,0xD0,0xF8,0x00,0x00,0x03};

extern uint8_t  m_localMAC[6];

extern int m_authenticationMode;

if (m_authenticationMode==1) memcpy(broadPackage,StarAddr,6);

   else memcpy( broadPackage, StandardAddr, 6 );

memcpy( broadPackage+6, m_localMAC, 6 ); //填充MAC地址

FillNetParamater( &broadPackage[0x17] );

fputs(">>searching for server...\n",stdout);

return (libnet_write_link(l,broadPackage, 0x3E8)==0x3E8)?0:-1;

}
复制代码

注释说的很清楚，这是用来寻找服务器的广播包。
显然这应该是数据链路层的帧，按照帧的格式，前6字节是目的mac，按照我的理解，目的
mac全1才是广播啊，在本函数中，不管m_authenticationMode是什么，目的mac都不会是全
1啊，为什么是广播呢？
望大侠赐教
thx

以我的所知，以太网的帧都是广播的。你说的全1广播，指的是IP分组吧。你觉得呢？

nait · 发表于 2005-6-19 23:54:46

呵呵，搞定了，原来这是个多播地址，注释写错了

@Illidan
你的理解有问题
以太网的帧并没有规定是要广播还是单播，这依赖于实现，具体说就是硬件
一般用集线器相连，是广播，用交换机相连，是单播。
广播效率底，同一时间总线上只能有一台主机传输信息，需要载波监听之类的技术，而且不安全
所以现在交换机比较好

Illidan · 发表于 2005-6-20 08:45:20

Post by nait
呵呵，搞定了，原来这是个多播地址，注释写错了

@Illidan
你的理解有问题
以太网的帧并没有规定是要广播还是单播，这依赖于实现，具体说就是硬件
一般用集线器相连，是广播，用交换机相连，是单播。
广播效率底，同一时间总线上只能有一台主机传输信息，需要载波监听之类的技术，而且不安全
所以现在交换机比较好

多谢，是我理解错了, hoho。而且广播的帧的目标MAC确实全1，真正的全1，IP分组广播也只是把host-id全置1而已，net-id并不变。
MAC地址也有多播这一类吗？你能多介绍一些不？

nait · 发表于 2005-6-20 23:27:45

以太网的多播地址特征是mac地址的第一个字节的最低位为1,以太网的多播是硬件实现的，更多的我也不知道了，我也正在查找这方面的资料

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