reading the release notes for CUCM 6.01a (http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/rel_notes/6_0_1/601cmrn.html) I saw, that CUCM supports Call Forward All (CFwdAll) loop prevention.
So if user A (DN 1000) forwards to B (DN 2000) and User B forwards to A, there should appear a message on the phone of user B saying "CFwdAll Loop detected".
I tried this with CUCM 6.0.1-2000-3 and it doesn't work. There is no Service Parameter, nothing.
Does anyone know how to activate this?