2. 计算机
  3. Anytime a host or a router has an IP datagram to send to another host or router，it has the (71)________________ address of th

Anytime a host or a router has an IP datagram to send to another host or router，it has the (71)________________ address of th

admin2020-05-13  25
问题 Anytime a host or a router has an IP datagram to send to another host or router，it has  the  (71)________________  address of the receiver．This address is obtained from the DNS if the sender  is the host or it is found in a routing table if the sender is a router．But the IP datagram  must be (72)________________  in a frame to be able to pass through the physical network．This means that  the sender needs the  (73)________________ address of the receiver．The host or the router sends an ARP  query packet．The packet includes the physical and IP addresses of the sender and the IP  address ofthe receiver．Because the sender does not know the physical address ofthe receiver，the  query is (74)________________ over the network．Every host or router on the network receives and processes the  ARP query packet, but only the intended recipient  recognizes its IP address and sends back an ARP  response packet．The response packet contains the recipient’s IP and physical addresses．Thepacket  is (75)________________ directly to the inquirer by using the physical address received in the query packet．
选项 A、multicast
B、unicast
C、broadcast
D、multiple unicast
答案B
解析 每当一个主机或路由器需要向另一个主机或路由器发送IP数据报时，它具有接收方的逻辑地址。如果发送方是主机，则从DNS获取此地址；如果发送方是路由器，则在路由表中找到此地址。但是IP数据报必须封装在一个帧中，才能通过物理网络。这意味着发送方需要接收方的物理地址。主机或路由器发送一个ARP查询包，它包括发送方的物理地址、IP地址以及接收方的lP地址。由于发送方不知道接收方的物理地址，所以通过网络广播进行查询。网络上的每个主机或路由器都接收和处理ARP查询数据包，但只有目标接收方识别出其IP地址并发回一个ARP响应数据包。这个数据包包含接收方的IP地址和物理地址，它通过从查询数据包中得到的物理地址直接单播到发送方。
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