ipnat opens the filename given (treating "-" as stdin) and parses the file for a set of rules which are to be added or removed from the IP NAT.
Each rule processed by ipnat is added to the kernels internal lists if there are no parsing problems. Rules are added to the end of the internal lists, matching the order in which they appear when given to ipnat.
Note that if ipf(8) is not enabled when NAT is configured, it will be enabled automatically, as the same kernel facilities are used for NAT functionality. In addition, packet forwarding must be enabled.