The ping fails, and ATM debug show traffic is going out and not coming back. Sending 2, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds: lt-7507b# debug atm packet interface a1/0.1 vc 0/85ĭisplaying packets on interface ATM1/0 VPI 0, VCI 85 only Let's shut down the ATM interface at the other router lt-7200b. If loopback is not set, those cells will not be loopbacked to us. Note: To illustrate the loopback mechanism, we will show that we can send ATM cells on the PVC. Received 0 broadcasts, 0 runts, 0 giants, 0 throttlesģ3 input errors, 33 CRC, 0 frame, 0 overrun, 0 ignored, 0 abortġ44191 packets output, 2138298 bytes, 0 underrunsĠ output errors, 0 collisions, 0 interface resetsĠ output buffer failures, 0 output buffers swapped out Output queue 0/40, 0 drops input queue 0/75, 0 dropsĥ minute input rate 0 bits/sec, 0 packets/secĥ minute output rate 0 bits/sec, 0 packets/secġ63861 packets input, 3164940 bytes, 0 no buffer Last clearing of "show interface" counters never Reliability 255/255, txload 1/255, rxload 1/255Ģ048 maximum active VCs, 1024 VCs per VP, 1 current VCCs Example 1īefore loopback diagnostic is set on the interface LT-7507b To do this, specify the atm clock internal setting in the main interface configuration. Note: To ensure proper clocking, set the router as the clock source. Note: Tx=transmit interface and Rx=Receive interface. To see loopback information for non-ATM interfaces, please click here and scroll down to the section on Special Serial Line Tests. Figure 1 and Example 1 illustrate how that process. The loopback diagnostic command under an ATM interface of a Cisco router causes traffic going out of the interface to come back to the router. We will use the following network to illustrate the loopback modes. If you are working in a live network, ensure that you understand the potential impact of any command before using it. All of the devices used in this document started with a cleared (default) configuration. The information presented in this document was created from devices in a specific lab environment. This applies only to the main interface, not the subinterface. The LANE modules support loopback line and other Cisco routers support both modes. The AIP supports loopback diagnostic while PA-A1, PA-A2 and PA-A3 support both modes. The examples in this document do not require any particular software versions. The information in this document is based on the software and hardware versions below. There are no specific prerequisites for this document. Refer to Cisco Technical Tips Conventions for more information on document conventions. Loopback line - this helps determine if there is a problem with the service provider. Loopback diagnostic - this helps you determine if your interface is working properly. This document examines the two types of loopbacks on Cisco router ATM interfaces: Loopbacks are an important part of troubleshooting they are used to isolate the fault on and end-to-end circuit (especially when the circuit is down).
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