tailieunhanh - ccna practical cisco routers phần 4

AppleTalk là tương tự như Ethernet ở chỗ nó là một kiến trúc mạng thụ động. AppleTalk sử dụng nhà cung cấp Sense truy cập nhiều với detection-CSMA/CA va chạm. Về cơ bản các máy tính ngồi trên mạng và lắng nghe để xác định xem dây là rõ ràng. | PART II Logical Interfaces CHAPTER 6 Because the router serves as such an important link between internetworks you don t want it dumping data packets if a particular physical interface goes down on the router. So the Loopback virtual interface is created and configured as the termination address for the Border Gateway Protocol BGP sessions. In this way the traffic is processed locally on the router which assures you that the packets get to their final destination. Null Interfaces Another logical interface is the Null interface. It is set up on a router using the appropriate router commands and serves as a brick wall that can be used to keep out certain traffic. For example if you don t want traffic from a particular network to move through a particular router but move through the internetwork by other routes you can configure the Null interface so that it receives and dumps any packets that the network sends to the router. Normally Access lists discussed in Chapter 14 Filtering Router Traffic with Access Lists are used to filter traffic on an internetwork and define valid routes for certain networks. The Null interface is pretty much a sledgehammer approach to a process that is normally handled with jeweler s tools. Tunnel Interfaces A Tunnel interface is another logical interface that can be used to move packets of a particular type over a connection that doesn t typically support these types of packets. For example a Tunnel interface can be set up on each of two routers that are responsible for routing AppleTalk packets from their LANs. These two routers are con -nected by a serial connection see Figure . The Tunnel interface can be configured to route IP. And although AppleTalk would not be typically routed over an IP interface the AppleTalk packets are encapsulated stuffed in a generic envelope and then moved across the Tunnel as if they were IP packets. Cisco routers provide the Generic Route Encapsulation Protocol GRE which handles the encapsulation of .

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