ccna 2 opcion b

ccna 2 opcion b.3. Layer 2 Problems on the Access Link (Step 2)If a router's physical interface line state is up, but its line protocol state (status code 2) is down, there is usually a Layer 2 problem on the link between that router and the local Frame Relay switch. For Frame Relay interfaces, the most typical problems are related to the encapsulation command or Frame Relay LMI.Potential problems associated with the encapsulation command are very easy to check. If a router's serial interface configuration ignores the encapsulation frame-relay interface subcommand, but this physical access link is working properly, the physical interface is placed in the up/down state. If the configuration is not available, you can view the configured encapsulation type in the first few lines of the output with the showinterfaces command.Other potential problems are related to LMI. LMI status messages are transmitted between the router (DTE) and the frame relay switch (DCE) for the following two important purposes........ For the DCE to be able to inform the DTE about each VC's DLCI and its status.. To provide a survivability feature that enables the DTE and DCE to easily inform each other when this access link is no longer capable of transmitting traffic. ''When the router physical link is in the up/down state. this link itself can work. but the router stops listening for LMI messages from the switch. And when this interface is not in the up/up state, the router will not try to send any IP data packets from this interface, so all pings will fail at this point.The router may stop receiving LMI messages from the switch due to various normal reasons or errors. The normal and reasonable use of the LMI survive feature is that when there is a real problem with that link and it cannot deliver any data, the router can notice that the survive message is lost and thus shut down the link. This allows the router to use an optional route, assuming of course that an optional route exists. However, the router may also stop receiving LMI messages and shut down the interface due to the following errors.LMI is disabled on the switch, but enabled on the router, and vice versa.Configure different LMI types on the router and switch (using the frame-relayImi-typetype physical interface subcommand) such that the router and306 Chapter 14 Implementing Frame Relay Frame Relay switches cannot understand other LMI information.