A user directory number is configured to forward all calls to a cell phone, but calls are not successfully forwarding. Which Cisco Unified Communications Manager setting requires reconfiguration?

The DN External Mask controls the calling party number presentation (CLID) for outbound calls from that DN and has no effect on whether a forwarded call can be routed to an external destination.

The DN Route Partition determines which devices with the appropriate CSS can reach that directory number; it governs inbound reachability of the DN, not the routing of calls forwarded by that DN.

The DN Calling Search Space controls which route patterns the phone can dial directly; CUCM uses the separate CFA CSS for forwarded calls, so the DN CSS is not evaluated during the forwarding routing decision.

The CFA Calling Search Space is a dedicated CSS applied specifically to forwarded calls; when a DN forwards to a cell phone, CUCM uses the CFA CSS to route the forwarded leg, so if the CFA CSS does not include a partition with a matching external route pattern, the forwarded call cannot reach the PSTN and will fail.