void ArpRequest (void)

来源：互联网发布：网络受限怎么办编辑：程序博客网时间：2024/05/16 19:36

void ArpRequest (void)
{
   int i;
   volatile uchar *pkt;
   ARP_t *arp;

#ifdef ET_DEBUG
   printf ("ARP broadcast %d\n", NetArpWaitTry);
#endif
   pkt = NetTxPacket;

pkt += NetSetEther (pkt, NetBcastAddr, PROT_ARP); //设置帧头（设置帧头（广播地址，本机mac，协议）

   arp = (ARP_t *) pkt;

   arp->ar_hrd = htons (ARP_ETHER);               //设置目标地址硬件类型
   arp->ar_pro = htons (PROT_IP);                     //设置目标地址上层协议为IP协议
   arp->ar_hln = 6;                                              //设置目标地址硬件地址长度
   arp->ar_pln = 4;                                              //设置目标地址上层协议地址长度（IP地址长度）
   arp->ar_op = htons (ARPOP_REQUEST);       //操作类型

   memcpy (&arp->ar_data[0], NetOurEther, 6);       /* source ET addr   */                //本机mac地址
   NetWriteIP ((uchar *) & arp->ar_data[6], NetOurIP);   /* source IP addr   */           //本机ip地址
   for (i = 10; i < 16; ++i) {
       arp->ar_data[i] = 0;               /* dest ET addr = 0     */                                         //目标mac地址=0
   }

   if ((NetArpWaitPacketIP & NetOurSubnetMask) !=
        (NetOurIP & NetOurSubnetMask)) {
       if (NetOurGatewayIP == 0) {
           puts ("## Warning: gatewayip needed but not set\n");
           NetArpWaitReplyIP = NetArpWaitPacketIP;           //不在同一网段，且没有网关-----目的ip地址
       } else {
           NetArpWaitReplyIP = NetOurGatewayIP;              //不在同一网段，且已设网关-----网关地址
       }
   } else {
       NetArpWaitReplyIP = NetArpWaitPacketIP;               //在同一网段-------------------------目的ip地址
   }

   NetWriteIP ((uchar *) & arp->ar_data[16], NetArpWaitReplyIP);                     //写入ar_data[16]
   (void) eth_send (NetTxPacket, (pkt - NetTxPacket) + ARP_HDR_SIZE);
}