The Route 53 resolver is the DNS service for VPCs that integrates with your data center. Connectivity needs to be established between your data center DNS and AWS using a Direct Connect (DX) or a Virtual Private Network (VPN) connection.    You configure endpoints for DNS queries into and out of VPCs. Endpoints are configured through IP address assignment in each subnet needing the Route 53 Resolver. 

Inbound queries allow DNS queries that originate in your data center to resolve AWS-hosted domains.  

Outbound DNS queries are enabled using conditional forwarding rules. Domains hosted in your data center can be configured as forwarding rules in Route 53 resolver.  Rules trigger when a query is made to one of those domains and the request is forwarded to your data center.  This recursive DNS for your VPCs controls how DNS queries are handled between your VPCs and your data center. 

Finally, the Route 53 Resolver DNS firewall is a managed firewall service for DNS queries that start in your VPCs.  You use a firewall rule group to define how Route 53 Resolver DNS firewall inspects and filters traffic coming from your VPC.  Each rule consists of a domain list to inspect in DNS queries and an action to take when a query results in a match.  You can allow a matching query to go through, allow it to go through with an alert or you can block it and respond with a default or a custom response.  To begin the filtering you associate the rule group to the VPCs you want to protect.  Route 53 resolver DNS firewall will apply your defined filtering rules to the outgoing VPC traffic.