Using Loopback Commands - Cisco ASR 1000 Series Software Configuration Manual

Troubleshooting the ATM SPAs

Using loopback Commands

The loopback commands place an interface in loopback mode, which enables you to use the ping command
to send packets through the local interface and line, so as to test connectivity. These commands are especially
useful when an interface is experiencing a high number of cyclic redundancy check (CRC) errors, so that you
can pinpoint where the errors are occurring.
The following describes different loopback tests:
Using the loopback diagnostic Command to Create a Local Loopback
To perform a local loopback test, in which the transmit data is looped back to the receive data at the physical
(PHY) layer, use the loopback diagnostic command on an ATM interface. This loopback tests connectivity
on the local ATM interface, verifying that the interface's framing circuitry and segmentation and reassembly
(SAR) circuitry is operating correctly. This loopback, however, does not test the interface's optics circuitry
and ports.
If an ATM interface is currently connected to another ATM interface and passing traffic, shut down the
Tip
remote ATM interface before giving the loopback diagnostic command on the local ATM interface.
Otherwise, the remote interface continues to send traffic to the local interface, and the remote network
could also start reporting interface and network errors.
SUMMARY STEPS
1. Router# configure terminal
2. Router(config)# interface atm slot /subslot/port
3. Router(config-if)# loopback diagnostic
4. Router(config-if)# atm clock internal
5. Router(config-if)# end
6. Router# show interface atm slot /subslot/port
7. Router(config-if)# ping ip-address [repeat count ] [data hex ] [size datagram-size ]
8. Router# show interface atm slot /subslot/port
9. Router(config)# interface atm slot /subslot/port
10. Router(config-if)# no loopback diagnostic
DETAILED STEPS
Command or Action
Step 1 Router# configure terminal
Step 2 Router(config)# interface atm slot
/subslot/port
OL-14127-17
Purpose
Enters global configuration mode.
Enters interface configuration mode for the indicated port on the specified ATM
SPA card.
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Using loopback Commands
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