Using debug and system diagnostic commands

You can perform the following operations related to debugging features:

To enable debugging on a feature, use the debug command in privileged EXEC mode.
```
device# debug feature required-keywords
```

To check whether debugging is enabled on a feature, use the show debug command in privileged EXEC mode.
```
device# show debug feature
```

To disable debugging, use the no debug command.

device# no debug feature required-keywords

Use caution when debugging in real time on a production device, because real-time debugging is CPU-intensive.

We recommend checking the command output on a lab device first, and then if the output looks acceptable, enable it on the production device to get more data. In addition, to reduce CPU load, we recommend using keywords such as events and summary that limit the extent of debugging rather than more comprehensive options such as detail and all.

Debugging operations are used mainly for debugging control plane protocols such as LACP and LLDP. For example, to view received LLDP packets on the console, use the following command:

device# debug lldp packets all rx

If the device is accessed through Telnet, enable logging using a terminal monitor.

The following are the most frequently used debug commands:

debug dot1x packet
debug lacp pdu [ rx | tx ]
debug lldp packet { all | ethernet slot/port }
debug spanning-tree bpdu [ rx | tx ]