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但问题是客户还没有IP地址,如何接收目标地址为服务器所分配的地址的应答包呢? \r\n\r\n这个问题问得好,请看下面的两段话,针对您的疑问给出了明确的答案。\r\n\r\nA BOOTP server that receives the request looks up several pieces of configuration information for the computer that issued the request, places the information in a single BOOTP Response message, and returns the reply to the requesting computer. Thus, in a single step, a computer can obtain information such as the computer\'s IP address, the server\'s name and IP address, and the IP address of a default router.\r\n\r\nLike other protocols used to obtain configuration information, BOOTP broadcasts each request. Unlike other protocols used for configuration, BOOTP appears to use a protocol that has not been configured: BOOTP uses IP to send a request and receive a response. How can BOOTP send an IP datagram before a computer\'s IP address has been configured? The answer lies in a careful design that allows IP to broadcast a request and receive a response before all values have been configured. To send a BOOTP datagram, IP uses the all-1\'s limited broadcast address as a DESTINATION ADDRESS , and uses the all-0\'s address as a SOURCE ADDRESS . If a computer uses the all-0\'s address to send a request, a BOOTP server either uses broadcast to return the response or uses the hardware address on the incoming frame to send a response via unicast. (The server must be careful to avoid using ARP because a client that does not know its IP address cannot answer ARP requests.)\r\n\r\nThus, a computer that does not know its IP address can communicate with a BOOTP server. \r\n\r\n |
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