In NAT mode, the guest network interface is assigned to the IPv4 range 10.0.x.0/24 by default where x corresponds to the instance of the NAT interface +2. So x is 2 when there is only one NAT instance active. In that case the guest is assigned to the address 10.0.2.15, the gateway is set to 10.0.2.2 and the name server can be found at 10.0.2.3.

If the NAT network needs to be changed, use the following command:

$ VBoxManage modifyvm VM-name \
--natnet1 "192.168/16"

This command would reserve the network addresses from 192.168.0.0 to 192.168.254.254 for the first NAT network instance of VM-name The guest IP would be assigned to 192.168.0.15 and the default gateway could be found at 192.168.0.2.