ANS-C01 Hybrid Routing and Cloud Connectivity Implementation Guide

Hybrid connectivity implementation questions on ANS-C01 are about making the enterprise path work under real routing, security, and validation constraints. The exam expects you to know how Direct Connect, Site-to-Site VPN, BGP, virtual interfaces, Direct Connect Gateway, Transit Gateway, customer gateways, and DNS fit together after the architecture has already been chosen.

The current AWS task statement is to implement routing and connectivity between on-premises networks and the AWS Cloud. The official scope includes configuring existing on-premises networks, static and dynamic routing, accelerated VPN, Direct Connect physical and logical requirements, VLANs, gateways, routing behavior, Transit Gateway Connect, SD-WAN-style integration, hybrid DNS, and connectivity testing.

What the exam is really testing

Implementation questions often fail at the edge between AWS and the enterprise router. The service can be correct while the VIF type, BGP advertisement, route priority, or return path is wrong.

Hybrid implementation chooser

Implementation sequence

Use this sequence for hybrid routing scenarios.

    flowchart LR
	  R["Requirement: private, encrypted, scalable, or SD-WAN"] --> T["Transport: DX, VPN, accelerated VPN, or TGW Connect"]
	  T --> A["AWS attachment: VGW, TGW, DXGW, or Cloud WAN"]
	  A --> B["BGP/static routes and prefix policy"]
	  B --> S["Security, DNS, and return path"]
	  S --> V["Validate metrics, routes, flows, and failover"]

The exam usually hides the miss in one of the middle boxes. For example, a Direct Connect link may be up, but the wrong VIF type or missing BGP prefix advertisement makes the application path fail.

Direct Connect implementation details

Direct Connect is not implemented by saying “create DX.” The logical construct matters.

The VIF type is a high-value exam clue. A private VIF is not the same thing as a transit VIF, and a public VIF solves a different problem from private VPC reachability.

Site-to-Site VPN implementation details

VPN implementation questions usually test customer gateway configuration and routing model.

AWS recommends BGP-capable devices when available because BGP provides route exchange and liveness detection that can assist failover between tunnels. Static routing is still valid when the device cannot run BGP or the prefix set is intentionally small and stable.

Static routing versus BGP implementation

Do not treat BGP as automatically correct. The implementation still needs the right ASNs, peer addresses, advertisements, accepted prefixes, and route preference.

Transit Gateway Connect and SD-WAN integration

Transit Gateway Connect appears when the enterprise already uses SD-WAN appliances or overlay networking. It supports GRE tunnels and BGP for dynamic routing to integrate third-party appliances or SD-WAN into a Transit Gateway design.

Use it when:

• the scenario explicitly mentions SD-WAN appliances or overlay networks
• dynamic route exchange through appliance peers is required
• GRE and BGP are part of the intended integration
• Transit Gateway is the hub for AWS-side routing

Avoid it when a normal Site-to-Site VPN, Direct Connect, or basic TGW attachment satisfies the requirement without adding an overlay appliance model.

Hybrid DNS is part of connectivity

Task 2.1 includes hybrid DNS because a path is not useful if applications cannot resolve names on the other side.

Do not troubleshoot only BGP when the real symptom is a failed DNS query across a working hybrid route.

Route priority and return path

Hybrid implementations often fail because the forward path and return path do not agree.

ANS-C01 strongly rewards answers that verify the return path instead of only configuring the forward route.

Validation and evidence

Hybrid connectivity is not complete until the implementation is proven.

If a proposed answer stops after “create the connection,” it is not strong enough for the implementation domain.

Common scenario patterns

Exam eliminations

Troubleshooting order

When hybrid connectivity fails after implementation, use this order:

1. Confirm the intended source, destination, protocol, port, and application name.
2. Verify physical or tunnel state: DX connection/VIF or VPN tunnel.
3. Verify routing session: BGP state, static routes, advertised prefixes, accepted prefixes, and path preference.
4. Check AWS-side route tables: VGW/TGW route propagation, TGW association, VPC subnet route, and return path.
5. Check on-premises routes, firewall policies, NAT, and customer gateway behavior.
6. Check DNS if the symptom uses names rather than IPs.
7. Validate with metrics, flow logs, Network Manager, Route Analyzer/Reachability Analyzer where applicable, and controlled failover tests.

This order prevents changing security groups or DNS records before proving the link, route exchange, and return path.

Sample exam question

A company has a Direct Connect connection to AWS and must connect many VPCs attached to a Transit Gateway. The team created a private virtual interface to a virtual private gateway and expected all Transit Gateway VPCs to be reachable. The BGP session is up, but only the single VPC associated with the virtual private gateway can be reached. Which change is strongest?

• Add CloudFront in front of the private workloads.
• Replace all BGP routes with static routes on the customer router.
• Use a transit virtual interface associated through a Direct Connect Gateway to the Transit Gateway, then validate Transit Gateway route tables and VPC subnet routes.
• Create a public hosted zone for every private workload.

Answer: Use a transit VIF through Direct Connect Gateway to Transit Gateway.

Why: A private VIF to a virtual private gateway is VPC-oriented. The requirement is hybrid access to many VPCs through Transit Gateway, which points to a transit VIF and Direct Connect Gateway/TGW implementation. Static routes do not fix the wrong VIF/attachment model. CloudFront and public hosted zones solve different problems.

Fast decision rule

For ANS-C01 hybrid implementation, choose the transport, then verify the AWS attachment, VIF or tunnel type, route exchange, prefix policy, security boundary, DNS path, and validation evidence. Use private VIF for VGW/VPC private access, transit VIF for Transit Gateway through Direct Connect Gateway, public VIF for public AWS services, Site-to-Site VPN for encrypted internet transport, and Transit Gateway Connect for SD-WAN/GRE/BGP appliance integration.

Quiz

Continue with 2.2 Multi-Account, Multi-VPC, and Multi-Region Connectivity Implementation to apply the hybrid implementation model across many accounts and VPCs.