The router inspecters the packet’s IP address and performs  (1)   lookup to see if the destination end station resides on the local(physically connected)network, typically called an IP subber.  (2)   usually is assignted to each of the router’s network interface. If the destination IP address is local, the router searches an internal store of IP address and local-device Media Acess Control(MAC) address. This store is known as  the  (3)   cache. Address Resolution rotocol(ARP)is the universal tool for matching IP addresses to MAC address. If the destination’s MAC address appears, the router installs that MAC address in the pachet header(removing its own MAC address because that’s no longer needed) and sends the packet to the destional end station.
   In the event that the destional MAC address does not appear in the ARP cache-it might have timed out, for instance-the router must broadcast an ARP request to the subnet referenced by the packet’s destional IP address. The end station with that IP address responds, sending back its MAC address. The router updates its cache, installs the new MAC address into the  (4)   and launches the packet. If the router table lookup shows that the packet is destined for a non-local subnet, the router forwards the packet to the next-hop  router using the-hop router’s MAC address.Routing tables are continuously built and rebuilt by intelligent discovery protocols, such as Routing Information Protocol or Open Shortest Path First(OSPF).Each router’s routing table shows the best route to the destination address: for address that may be severd hops away, it shows  (5)   next-hop router.
 
(1) A. a router table      B.a signal    C.an e-mail        D.a file
(2) A. A TCP  subnet    B.IP header   C. An IP subnet    D.TCP/IP
(3) A.OSPF     B. Address Resolution Protocol(ARP)     C.MAC      D.RIP
(4) A.small packet      B.space      C.packet header     D.packet tailor
(5) A.the fewest        B.the worst   C.the least          D.the best #p#
答案:1、A  2、C  3、B  4、C  5、D

參考譯文：

路由器檢測(cè)包的IP地址，并執(zhí)行一個(gè)路由器查表，看看目的地端站駐留在本地（物理連接）網(wǎng)絡(luò)，通常稱為IP subber 。通常一個(gè)IP子網(wǎng)是被定義的每個(gè)路由器的網(wǎng)絡(luò)接口。如果目的IP地址是本地，路由器搜索內(nèi)部存儲(chǔ)的IP地址和本地設(shè)備的媒體訪問(wèn)控制（ MAC ）地址。這家店面被稱為地址解析協(xié)議（ ARP ）高速緩存。地址解析協(xié)議（ ARP協(xié)議）是普遍的工具匹配IP地址的MAC地址。如果目的地的MAC地址時(shí)，路由器的安裝MAC地址在包標(biāo)題（除去自己的MAC地址，因?yàn)檫@不再需要）和發(fā)送數(shù)據(jù)包的目的端站。
   如果目的MAC地址沒(méi)有出現(xiàn)在ARP高速緩存，它有可能超時(shí)，例如，路由器必須播出一個(gè)ARP請(qǐng)求的子網(wǎng)中所引用的數(shù)據(jù)包的目的 IP地址。年底站與IP地址的回應(yīng)，發(fā)送回其MAC地址。路由器更新其緩存，安裝新的MAC地址的數(shù)據(jù)包標(biāo)頭和發(fā)射的數(shù)據(jù)包。如果路由器查表表明，包注定是一個(gè)非本地子網(wǎng)，路由器轉(zhuǎn)發(fā)數(shù)據(jù)包到下一跳路由器使用一跳路由器的MAC 地址。路由表不斷興建和改建的智能發(fā)現(xiàn)協(xié)議，如路由信息協(xié)議或開(kāi)放式最短路徑優(yōu)先（ OSPF ） 。每臺(tái)路由器的路由表顯示的最佳途徑到目的地地址：地址可能自動(dòng)選擇，它表明的最佳下一跳路由器。