Specify the Nat option, which can take one of the following values:
ALL_SUBNETWORKS_ALL_IP_RANGES: All of the IP ranges in every
Subnetwork are allowed to Nat.
ALL_SUBNETWORKS_ALL_PRIMARY_IP_RANGES: All of the primary IP
ranges in every Subnetwork are allowed to Nat.
LIST_OF_SUBNETWORKS: A list of Subnetworks are allowed to Nat
(specified in the field subnetwork below) The default is
SUBNETWORK_IP_RANGE_TO_NAT_OPTION_UNSPECIFIED. Note that if this
field contains ALL_SUBNETWORKS_ALL_IP_RANGES or
ALL_SUBNETWORKS_ALL_PRIMARY_IP_RANGES, then there should not be
any other Router.Nat section in any Router for this network in
this region.