ccna 1 questions

ccna 1 questions.Figure 13-7 Two PVCs, with one DLCI at each end of each PVCIn this example, the PVC between Routers A and B is assigned two DLCIs by the service provider. router A uses local DLCI 41 to identify the PVC, while one end of router B uses DLCI 40 to identify the same PVC. similarly, the PVC between routers A and C is assigned two local DLCIs, one at each end. One for each end. Router A uses 42, and Router C uses 40o.The service provider can use any DLCI value within the range of legal values, with one exception. The local DLCI on a single access link of Instrument S must be unique among all PVCs using a physical Frame Relay access link, because the Frame RelayDLCI has significant locality significance.Because the service provider is responsible for selecting the DLCI,the enterprise network administrator does not need to worry about a situation where the DLCI value is incorrectly selected. By understanding the above techniques, it is clear that the DLCI value must be unique on each physical access link connecting the router to the Frame Relay network. As shown in Figure 13-7, the service provider defines two PVCs for a Frame Relay incoming link through Router A: a PVC with a local DLCI of 41 and a local DLCI of 42. If another PVC is added that connects to Router A, the server provider cannot use 41 or 42 as the local DLCI for the Router A access link.The local router can only see or know the local DLCJ. when the user configures the router, only the local DLCI value can be configured, not the DLCI at the other end of the PVC. similarly, the show command can only display the local DLCI value.12.2 Basic Content 279Forwarding frames using a DLCI fieldThere is a very distinct difference between the entire forwarding process that DCLI relates to compared to the other two common addresses discussed in the CCNA (MAC and IP). The Ethernet header includes the source and destination MAC addresses, while the IP header includes the source and destination IP addresses. However, the Frame Relay header has only one DCLI field, which does not identify the source and destination, except for the PVC.To gain some insight into how a service provider forwards Frame Relay frames, consider the case where the service provider knows the local DLCI used at each end of the PVC, and the access links connecting those routers. For example, as shown in Figure 13-8, the provider knows that there is a PVC between Router A and Router B, and knows that the local DLCI41 is used on Router A's side and the DLCI40 is used on Router B's side. Based on these facts, Figure 13-8 shows what happens when Router A sends a frame to Router B.