CCNP2 - Implementing Secure Converged Wide-area Networks v5.0

Transcription

1 Configuring a DSL ATM Interface Figures and show the steps you use to configure a DSL ATM interface. Use the dsl operating-mode auto interface configuration command to specify that the router automatically detects the DSL modulation that the service provider is using and sets the DSL modulation to match. An incompatible DSL modulation configuration can result in failure to establish a DSL connection to the DSLAM of the service provider. Use the pvc interface configuration command to set the virtual path identifier/virtual channel identifier (VPI/VCI) that is used by the DSL service provider, as shown in the pvc Parameters table. Settings for the VPI/VCI value on the Cisco router must match the configuration on the DSLAM of the service provider switch configuration. ATM uses the VPI/VCI to identify an ATM VC. Module 2: Teleworker Connectivity 52

2 pvc Parameters Parameter Vpi Vci Description VPI from the service provider VCI from the service provider The encapsulation method must correspond with the method configured on the aggregation router. The Encapsulation Commands table shows the available commands. Encapsulation Commands Command encapsulation aal5mux ppp dialer dialer pool-member number Description Sets the encapsulation for PPPoA, which uses AAL5 in the MUX mode Links the ATM interface to a dialer interface Use the dialer pool-member command to specify which dialer interfaces can use the ATM physical interface on the Cisco router. Figure shows an example of a complete PPPoA configuration. The example presents the complete PPPoA configuration with PAT, DHCP services, MTU adjustments, and static default routing. Module 2: Teleworker Connectivity 53

3 2.7 - Troubleshooting Broadband ADSL Configurations Troubleshooting Layers 1, 2, and 3 ADSL service problems can reside at Layer 1, Layer 2, or Layer 3. Troubleshooting should start by determining which ADSL service layer is failing. To determine which layer has a problem, use a bottom-up approach; that is, start troubleshooting at Layer 1 and move to subsequent layers as required. Figure illustrates this approach Determine Whether the Router Is Properly Trained to the DSLAM Start troubleshooting Layer 1 by verifying whether a Cisco Systems CPE router is trained to the DSLAM in the CO by using the show dsl interface atm command. When a router is successfully trained to the DSLAM, the modem status field has the value Showtime. Along with that value, the command also displays the upstream and downstream speed in kbps (in the row Speed, the Interleave or Fast columns will have a nonzero value). Figure is an example of the output from a properly trained modem. If the modem and router are properly trained, move troubleshooting efforts to Layer 2. Module 2: Teleworker Connectivity 54

4 When the router is not properly trained, as shown in the following output, the problem is at Layer 1, and a solution needs to be found at this layer. Router#show dsl interface atm 0 Line not activated: displaying cached data from last activation Log file of training sequence: <...rest of the output omitted...> Troubleshooting Layer 1 Issues You can monitor the status of the ATM interface on the router by checking the status of the Carrier Detect (CD) light on the router s interface panel: If the CD light is on, proceed to Layer 2 troubleshooting. If the CD light is off, continue with Layer 1 troubleshooting. Next, use the show interface atm privilege level command from the enable mode of the router to check the status of the ATM interface on the router. This command appears in Figure. If the ATM interface status is down and the line protocol is down, the router is not seeing a carrier on the ADSL line. Such a status usually indicates two possible issues: The active pins on the DSL wall jack may be incorrect. For example, the registered jack- 11 (RJ-11) connector provides an xdsl connection to an external media via a standard RJ-11 6-pin modular jack. The service provider may not be providing DSL service on this wall jack. The Cisco router uses a standard RJ-11 cable to provide the ADSL connection to the wall jack. The center pair of pins on the RJ-11 cable carries the ADSL signal (pins 3 and 4 on a 6-pin cable, or pins 2 and 3 on a 4-pin cable). Module 2: Teleworker Connectivity 55

5 If the wall jack is using the correct pins, and the ATM interface is still down and the line protocol is down, replace the RJ-11 cable between the DSL port and the wall jack. If the interface is still down and the line protocol is down after you have replaced the RJ-11 cable, contact the service provider to verify that ADSL service has been enabled on the wall jack you are using. The show interface atm command also shows whether the interface is administratively disabled. If such a case exists, enable the interface by using the no shutdown command under the interface configuration mode Determining the Correct DSL Operating Mode If everything that you have checked up to now in the Layer 1 troubleshooting procedure is verified and is operating properly, the next step is to ensure that the correct DSL operating mode is being used. Check with the service provider whether the DSLAM supports the particular DSL chipset (for example, Alcatel) and the configured modulation method of the deployed Cisco CPE DSL router. If the DSL modulation being used by the service provider is unknown, Cisco recommends using the default auto operating mode to autodetect the modulation type. Run the auto operating mode using this command (see the dsl operating-mode Parameters table for details): dsl operating-mode {auto ansi-dmt itu-dmt splitterless} dsl operating-mode Parameters Parameter auto ansi-dmt itu-dmt splitterless Description Configures the ADSL line after auto negotiating with the DSLAM located at the CO; this is the default operating mode Configures the ADSL line to use the ANSI T1.413 Issue 2 mode Configures the ADSL line to use the G mode Configures the ADSL line to use the G (G.lite) mode If problems persist and the router has been properly configured, proceed to Layer 2 examination and troubleshooting Troubleshooting Layer 2 Issues After establishing that Layer 1 is operating correctly, the troubleshooting can continue at Layer 2. First, check whether a permanent virtual circuit (PVC) is configured at the DSLAM by using the ping atm interface atm command. This command sends Operation, Administration, and Maintenance (OAM) F5 loopback packets to the DSLAM. A successful ping designates that a PVC is configured at the DSLAM. Module 2: Teleworker Connectivity 56

6 Next, check whether the correct VPI/VCI values are configured on the router, by using the debug atm events command. The output shows the VPI/VCI values that the DSLAM expects. During the debug process, use another working Internet connection and begin to ping the static IP address assigned by your Internet service provider (ISP). It is important that the ATM interface status is up, the line protocol is up, and that the IP address provided by the ISP is being pinged. If there is no output for 60 seconds, debugging the VPI/VCI values is probably incorrect and you should contact ISP support. Finally, verify the VPI/VCI values and make the necessary changes to the configuration. When you are finished with this troubleshooting task, turn off debugging by using the undebug all command Layer 2: Is Data Being Received from the ISP? If the VPI/VCI values are correct and the PVC is active, then the next step is to verify that data is being sent and received on the ATM interface. The show interfaces atm command shows the interface status and counters for incoming and outgoing packets. If the incoming and outgoing packet counters are incrementing, the router is receiving and sending packets from the ISP; therefore, data is received from the ISP and is sent to the ISP. Module 2: Teleworker Connectivity 57

7 Proper PPP Negotiation With Layer 1 set up properly, correct VPI/VCI in use, PVC active, and data being received and sent, the next step is to ensure that a PPP session is established properly between the Cisco CPE router and the aggregation router of the service provider. You can observe the PPP negotiation process by issuing the debug ppp negotiation and debug ppp authentication commands. PPP session setup occurs in three stages: 1. Link control protocol (LCP): A mandatory phase in which parameters to establish, configure, and test the data-link connection are negotiated. 2. Authentication: In this optional phase, authentication is performed with the authentication protocol (CHAP or PAP) agreed upon in LCP negotiation. 3. Network Control Protocol (NCP): This mandatory phase establishes and configures different network-layer protocols. The most common Layer 3 protocol negotiated is IP. The routers exchange IPCP messages to negotiate options specific to the IP protocol. The debug output in Figure shows the successful PPP session establishment. In case the PPP session does not come up successfully, there are four main points of failure in a PPP negotiation: Module 2: Teleworker Connectivity 58

8 There is no response from the remote device (aggregation router of the service provider). LCP is not opened. PAP or CHAP authentication failure occurs. IPCP failures PPPoE Simulation Practice PPPoE Simulation Practice e-lab Activity e-lab Activity: PPPoE Simulation This task will provide practice configuring a Cisco ADSL router for connectivity to an ISP using PPPoE. In addition, it will be necessary to configure Dynamic Host Configuration Protocol (DHCP) services for IP addressing of local PCs at the teleworker s location; also, basic Port Address Translation (PAT) will need to be configured. Summary This module concentrated on teleworkers and the ways to connect them to the enterprise network. The most common technologies, cable and variants of the DSL, are described in detail. The differences between PPPoE and PPPoA are described and details on how to configure and troubleshoot each method are included. The module also describes how to verify the configurations of broadband connections, and troubleshoot problems. Quiz 1. Module 2: Teleworker Connectivity 59

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