1.3.a Use IOS troubleshooting tools

1.3.a [i] debug, conditional debug

When the conditionally triggered debugging feature is enabled, the router generates debugging messages matching a given condition. For example , you may only want to see debugging messages for one interface or sub-interface. You can also turn on debugging for all interfaces that meet specified conditions.

Normally, the router will generate debugging messages for every interface, resulting in a large number of message that consume system resources and can make it difficult to find the specific information you need. By limiting the number of debugging messages, you can receive messages related to only the ports you want to troubleshoot.

You can use conditional debug as follows: router# debug condition interface < interface >

You can verify conditional debug configuration using show debug or show debug condition.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1347-1353).  Kindle Edition.

http://www.cisco.com/c/en/us/support/web/tools-catalog.html

rtr1#debug condition ?
called       called number
calling      calling
card         card
cpl          Cisco Provisioning Language debugging
glbp         interface group
interface    interface
ip           IP address
mac-address  MAC address
standby      interface group
username     username
vcid         VC ID
vlan         vlan
vrf          Virtual Routing and Forwarding