Core issue
The Catalyst 6500 Switch that runs Cisco IOS software uses Maintenance Operations Protocol (MOP) packets in order to advertize its existence to Digital Equipment Corporation machines that use the MOP protocol. A switch periodically broadcasts MOP packets in order to identify itself as a MOP host. As a result, MOP packets are counted, even when DECnet is not actively used.
The MOP is a Digital Equipment Corporation protocol that provides a way to perform primitive maintenance operations on DECnet systems. For example, MOP can be used to download a system image to a diskless station.
The MOP is enabled by default on the Cat6500.
Issue the show interfaces accounting command in order to check which interfaces send MOP messages.
Resolution
In order to resolve this issue, disable the MOP on all the MOP enabled interfaces:
Switch (config)#interface id
Switch (config-if)#no mop enabled
Switch (config-if)#no mop sysid
Note: There is no global command that disables MOP. It has to be disabled on an interface basis.
Refer to the Switch Sends Out Periodic DEC MOP Packets section of Troubleshooting Hardware and Common Issues on Catalyst 6500/6000 Series Switches Running Cisco IOS System Software for more information.
