Cisco Cisco IOS Software Release 12.2(27)SBC

One or more ATM-encapsulated interfaces must be enabled, and one or more of the following debug 
commands must be enabled, to use the ATM Conditional Debug Support feature:

Only the ATM debugging commands listed in the “Prerequisites for ATM Conditional Debug Support” 
section on page 2 can use the ATM Conditional Debug Support feature. 

Conditional debugging for virtual circuits (VCs) can be enabled only for permanent virtual circuits 
(PVCs). Switched virtual circuits (SVCs) are not supported.

You need to understand the following concept before using the ATM Conditional Debug Support feature: 

ATM Debugging Extended to the Virtual Circuit Level

The ATM debug commands are implemented either at the interface level or at the system level. The 
debug command output at these levels is not very useful when the user is interested in a particular set of 
VCs.

The Cisco IOS software has the infrastructure to support conditional debugging based on various filters 
that are set at the command-line interface (CLI). The conditional debugging infrastructure can filter out 
or suppress unwanted messages from the output of any existing debug command. The ATM Conditional 
Debug Support feature extends this infrastructure to support conditional debugging at the ATM VC level 
by extending the debug condition interface command with keywords that address specific virtual 
circuits. This feature can be implemented on top of conventional debugging, so that backward 
compatibility is ensured and at the same time applications can take advantage of conditional debugging 
where required. However, the extended debug condition interface command will have priority over the 
older version of the command; that is, a debug condition setting using the older debug condition 
interface command will be discarded as soon as a new debug condition is enabled on a virtual circuit.