STEERING POLICIES is A framework to define the traffic management behavior for your zones. Steering policies contain rules that help to intelligently serve DNS answers.
FAILOVER
Failover policies allow you to prioritize the order in which you want answers served in a policy (for example, Primary and Secondary). Oracle Cloud Infrastructure Health Checks are leveraged to determine the health of answers in the policy. If the Primary Answer is determined to be unhealthy, DNS traffic will automatically be steered to the Secondary Answer.
LOAD_BALANCE
Load Balancer policies allow distribution of traffic across multiple endpoints. Endpoints can be assigned equal weights to distribute traffic evenly across the endpoints or custom weights may be assigned for ratio load balancing. Oracle Cloud Infrastructure Health Checks are leveraged to determine the health of the endpoint. DNS traffic will be automatically distributed to the other endpoints, if an endpoint is determined to be unhealthy.
ROUTE_BY_GEO
Geolocation-based steering policies distribute DNS traffic to different endpoints based on the location of the end user. Customers can define geographic regions composed of originating continent, countries or states/provinces (North America) and define a separate endpoint or set of endpoints for each region.
ROUTE_BY_ASN
ASN-based steering policies enable you to steer DNS traffic based on Autonomous System Numbers (ASN).
DNS queries originating from a specific ASN or set of ASNs can be steered to a specified endpoint.
ROUTE_BY_IP
IP Prefix-based steering policies enable customers to steer DNS traffic based on the IP Prefix of the originating query.

Explanation
in Transit routing through a private IP in the VCN you set up an instance in the VCN to act as a firewall or intrusion detection system to filter or inspect the traffic between the on-premises network and Oracle Services Network.
The Networking service lets you implement network security functions such as intrusion detection, application-level firewalls In fact, the IDS model can be host-based IDS (HIDS) or network-based IDS (NIDS). HIDS is installed at a host to periodically monitor specific system logs for patterns of intrusions. In contrast, an NIDS sniffs the traffic to analyze suspicious behaviors. A signature-based NIDS (SNIDS) examines the traffic for patterns of known intrusions. SNIDS can quickly and reliably diagnose the attacking techniques and security holes without generating an over-whelming number of false alarms because SNIDS relies on known signatures.
However, anomaly-based NIDS (ANIDS) detects unusual behaviors based on statistical methods. ANIDS could detect symptoms of attacks without specific knowledge of details. However, if the training data of the normal traffic are inadequate, ANIDS may generate a large number of false alarms.