I think maybe a trap will be sent when interface is administratively or operational down, but which and how to config. Gurus, any direction?
A linkDown trap will be sent when an interface transitions from up to another state, and a linkUp trap will be sent when the interface transitions back to up.
See http://www.cisco.com/en/US/docs/ios/12_1/configfun/configuration/guide/fcd301.html#wp1001347 on how to configure an IOS device for traps. For example:
snmp-server enable traps
snmp-server host 184.108.40.206 traps version 1 public