Hi Masoud, there's a DDNS update queue in the zone structure. Access to it is protected by a mutex. Updates are processed in order they were added to the queue, and all the changes are processed into a single zone_update_t structure. That is basically a set of changes that is later applied using a RCU lock, as you correctly noted. Some hints for you: process_query.c:141: processing DDNS UPDATE packet zone.c:506: adding the DDNS change to the queue - you can see the DDNS mutex here update.c:131: process_normal function that processes the list and manages the actual update of the zone Cheers, Dominik On 04/08/2016 07:43 PM, masoud hematpour wrote: