Cisco IOS Cookbook, 2nd Edition

Setting Payload Scrambling on an ATM Circuit

Problem

You want to enable payload scrambling on your ATM circuit to prevent user data from being interpreted as an in-band control sequence.

Solution

The command to enable scrambling varies depending on the type of circuit. For a T3 ATM circuit, you must use the command atm ds3-scramble, as follows:

Router2#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#interface ATM0/0
Router2(config-if)#atm ds3-scramble
Router2(config-if)#exit
Router2(config)#end
Router2#

For E3 circuits, scrambling is actually enabled by default, but you can disable it with the no form of the command atm e3-scramble:

Router3#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router3(config)#interface ATM0/0
Router3(config-if)#no atm e3-scramble
Router3(config-if)#exit
Router3(config)#end
Router3#

Both of the preceding commands will scramble the ATM cells at the Physical Layer Interface Module (PLIM) on the ATM interface. You can also opt to scramble only the ATM cell’s payload as follows:

Router4#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router4(config)#interface ATM0/0
Router4(config-if)#atm scrambling cell-payload
Router4(config-if)#exit
Router4(config)#end
Router4#

Discussion

In Recipe 16.5, we mentioned that some types of network devices use in-band signaling to indicate that there are errors on the circuit. This can cause network problems if a switch responds ...