ccna 1 questions and answers

ccna 1 questions and answers.The figure shows 3 main steps. First, Router A decides to send the frame through the PVC connected to Router B. From Router A's point of view, Router A sends the frame through the PVC. From Router A's perspective, the only thing A knows about the PVC is the local DLCI41 used by the PVC, so A adds the DLCI41 to the header and sends the frame. In Step 2, the service provider does a lot of work, including looking at what they know about this PVC, forwarding the frame to Router B, and modifying the DLCI to 40. In Step 3, when the frame arrives at Router B, its DLCI has a value of 40. Router B is able to correctly determine that the frame arrived from Router A via the PVC because Router B only knows about this PVC, Its local DLCI (at Router B's end) is 40.Figure 13-8 Frame Relay forwarding: router A to router B. Note that when A sends the frame, A uses its own local DLCI value (41), and when B receives the frame, B sees the local DLCI of the same PVC (40).Now think about the case where router B returns the sent packet to router A to complete the whole process. Again, the router only knows the value of the local DLCI, so as shown in Figure 13-9, B sends the frame with DLCI 40, which DCLI identifies the PVC from A to B,The frame relay cloud modifies the DLCI to 41, and as a result, router A receives the frame with DLCI 41.The same scenario as above occurs on every PVC. Previously, there were two PVCs as shown in Figure 13-7, including the PVC from A to C with local DLCI 42 (side A) and 40 (side C). Figure 13-10 shows the local DLCI on two different directional frame transmissions: first from A to C, and then from C back to A.The figure does not show the operation of the Frame Relay cloud exchanging DLCI values, but the operation is still actually taking place. In step 1, router A forwards a frame using DLCI 42. In Step 2, but the frame is forwarded from the Frame Relay cloud to Router C, it has been changed to use DLCI 40, the local DLCI used by Router C for this PVC0 Similarly, in Step 3, Router C sends a frame using DLCI 40. The Frame Relay cloud changes the DLCI to 40, so at step 4, when the frame is forwarded from the cloud to Router A, the frame lists the local DLCI 42O for Router A280 Chapter 13 Understanding Frame Relay ConceptsFigure 13-9 Frame Relay Forwarding: Router B to Router AFigure 13-10 Frame Relay Forwarding Between Router A and Router C13.2.3 Network Layer Addressing Associated with Frame RelayFrame Relay networks have both similarities and differences compared to LAN and point-to-point WAN links. These differences introduce some additional considerations for transporting Layer 3 packets over a Frame Relay network. In particular, the Cisco application implementing Frame Relay defines three different options for assigning subnet and IP addresses on the Frame Relay interface.