Configuring existing on-premises name resolution with the AWS Cloud

Task Statement 2.1: Implement routing and connectivity between on-premises networks and the AWS Cloud.

📘AWS Certified Advanced Networking – Specialty

Introduction to Name Resolution in Hybrid Environments

Name resolution is the process of translating human-friendly names (like server.company.com) into IP addresses (10.0.1.5) that computers use to communicate.

When you connect your on-premises network (your company’s data center) to the AWS Cloud, you need to ensure that systems on both sides can resolve names correctly. Without proper name resolution, applications, services, or workloads in AWS might fail to communicate with your on-premises systems, and vice versa.

There are two main ways to configure name resolution for hybrid networks:

Forwarding DNS queries from AWS to on-premises DNS servers.
Forwarding DNS queries from on-premises to AWS-provided DNS (like Route 53 Resolver).

1. Using AWS Route 53 Resolver for Hybrid DNS

AWS Route 53 Resolver is a managed DNS service that allows hybrid name resolution between on-premises and AWS.

Key components:

Inbound Endpoints – These allow on-premises systems to query AWS-hosted DNS.
- Example: Your on-premises server wants to resolve app.internal.aws.com. It sends the query to Route 53 Resolver through the inbound endpoint.
- Useful when your applications in AWS need to be queried from on-premises.
Outbound Endpoints – These allow AWS-based systems to query on-premises DNS servers.
- Example: An EC2 instance wants to resolve server.onprem.company.com. The query goes through the outbound endpoint to your on-premises DNS server.
Rules – Route 53 Resolver lets you configure rules to forward DNS queries based on domain names.
- Example: Forward all queries ending with corp.internal to your on-premises DNS.
- Forward all queries ending with aws.internal to AWS.
Security – The endpoints can be attached to VPC security groups to control which resources can use them.

Exam Tip: Know the difference between inbound and outbound endpoints, and understand how rules work for domain-based query forwarding.

2. Integrating On-Premises DNS with AWS

Step 1: Identify the DNS hierarchy

On-premises typically uses Active Directory-integrated DNS or custom DNS servers.
AWS uses VPC-provided DNS (default for EC2 instances in a VPC) or Route 53 Resolver.

Step 2: Decide which queries go where

Queries for AWS-hosted services → AWS Route 53.
Queries for on-premises resources → on-premises DNS.

Step 3: Configure forwarding

From AWS to On-Premises:
- Create an outbound endpoint in Route 53 Resolver.
- Create a rule that forwards specific domains (like corp.company.com) to the on-premises DNS IPs.
From On-Premises to AWS:
- Use a conditional forwarder on your on-premises DNS server pointing to the Route 53 inbound endpoint IP addresses.

Exam Tip: AWS Certified Advanced Networking – Specialty exam may test your understanding of conditional forwarders vs rules in Route 53 Resolver.

3. Using Split-Horizon DNS (Optional for Advanced Setup)

Split-horizon DNS is when the same domain resolves differently depending on where the query originates.

Example:
- app.company.com resolves to 10.0.0.10 inside the VPC.
- The same app.company.com resolves to 192.168.1.10 on-premises.

This setup is common in hybrid environments to avoid exposing private IPs across networks.

Exam Tip: Know that Route 53 Resolver rules + VPC DNS settings can help achieve split-horizon DNS behavior in hybrid setups.

4. Important Configuration Considerations

VPC DHCP Options Sets
- Controls which DNS servers EC2 instances use in a VPC.
- Must point to Route 53 Resolver if using hybrid DNS forwarding.
Network connectivity
- DNS forwarding relies on Direct Connect, VPN, or Transit Gateway connectivity.
- Without connectivity, queries fail.
High availability
- Configure multiple inbound/outbound endpoints across subnets for redundancy.
Latency & performance
- Forward only necessary domains to avoid overloading on-premises DNS.
Security
- Use security groups and network ACLs to restrict access to DNS endpoints.

5. Example Flow (AWS to On-Premises)

EC2 in VPC queries internal.corp.com.
Query hits VPC DNS → forwarded to Route 53 Resolver outbound endpoint.
Outbound endpoint forwards query to on-premises DNS server via VPN/Direct Connect.
Response returns to EC2.

This ensures seamless hybrid DNS resolution for applications in AWS needing on-premises resources.

6. Exam Tips & Key Points to Remember

Understand Route 53 Resolver inbound vs outbound endpoints.
Know rules and conditional forwarders and when to use each.
Be able to explain DNS query flow in hybrid networks.
Understand VPC DHCP options set role in hybrid DNS.
Consider high availability and security when designing DNS for hybrid.
Be able to explain split-horizon DNS scenarios.

✅ Summary for Easy Understanding

Hybrid DNS = letting AWS and on-premises systems talk using names.
Route 53 Resolver handles forwarding queries in both directions.
Inbound endpoint = on-premises → AWS.
Outbound endpoint = AWS → on-premises.
Rules / conditional forwarders define which queries go where.
Ensure connectivity, security, and redundancy.