Routing fundamentals (for example, dynamic compared with static, BGP)

Task Statement 1.5: Design a routing strategy and connectivity architecture between on-premises networks and the AWS Cloud.

📘AWS Certified Advanced Networking – Specialty

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1. Types of Routing

Routing can be static or dynamic:

A. Static Routing

• Definition: Routes are manually configured on network devices (routers or virtual appliances).
• How it works: You define the destination network and the next hop (where packets should go).
• Advantages:
  • Simple to configure for small networks.
  • No extra protocol overhead; uses fewer resources.
• Disadvantages:
  • Does not automatically adjust if the network changes (e.g., link failures).
  • Hard to manage at scale.
• AWS Example:
  • In AWS Virtual Private Gateway (VGW) or Transit Gateway, you can configure static routes in the route table to direct traffic to your on-premises network.
  • Example: 10.0.0.0/16 -> on-premises VPN connection.

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B. Dynamic Routing

• Definition: Routes are automatically learned and updated using a routing protocol.
• How it works: Routers exchange information about network topology to adjust routes automatically.
• Advantages:
  • Automatically adapts to network changes or failures.
  • Easier to manage large or complex networks.
• Disadvantages:
  • Slightly more complex to configure.
  • Consumes more bandwidth and resources.
• AWS Example:
  • BGP (Border Gateway Protocol) is the primary dynamic routing protocol used between AWS and on-premises networks.
  • BGP allows AWS to advertise routes from your VPC to your on-premises network and vice versa.
  • Works with AWS Site-to-Site VPN or Direct Connect connections.

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2. Border Gateway Protocol (BGP)

BGP is key for hybrid networking with AWS.

• Type: Exterior Gateway Protocol (EGP), used to exchange routes between different autonomous systems (AS).
• Why it matters: AWS and your on-premises network are usually separate ASes, so BGP ensures both networks know how to reach each other dynamically.
• AWS Use Cases:
  • Site-to-Site VPN: BGP allows automatic failover between multiple VPN tunnels.
  • Direct Connect: BGP exchanges routes between your on-premises network and AWS for reliable high-speed connectivity.
• BGP Features:
  • Path Selection: Chooses the best route based on network policies and metrics.
  • Automatic Failover: If one path fails, BGP reroutes traffic automatically through another available path.
• AWS Specific Tip:
  • When using BGP with AWS VGW or Transit Gateway, you can use dynamic routing to avoid manually updating route tables when your network changes.

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3. AWS Routing Architecture Concepts

When connecting on-premises networks to AWS, routing decisions involve:

A. VPC Route Tables

• Direct traffic between subnets, internet, VPNs, and Direct Connect.
• Example:
  • Subnet route table: 0.0.0.0/0 -> IGW (internet gateway)
  • 10.0.0.0/16 -> VGW (on-premises network via VPN)

B. Transit Gateway

• Central hub to connect multiple VPCs and on-premises networks.
• Reduces complex peering configurations.
• Supports dynamic routing with BGP to automatically learn routes.

C. Route Propagation

• Allows AWS route tables to automatically receive routes from VPNs or Direct Connect.
• Reduces manual route configuration and mistakes.

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4. Key Considerations for Routing Strategy in Hybrid Networks

When designing your routing strategy for AWS certification:

1. Decide between static vs dynamic routing
   • Small, simple networks → static routing
   • Medium/large networks → dynamic routing with BGP
2. Plan route tables
   • Define routes for subnets, VPCs, and on-premises networks
   • Use route propagation where possible for efficiency
3. Redundancy
   • Always have multiple VPN tunnels or Direct Connect paths
   • BGP ensures automatic failover
4. Security
   • Only advertise required routes
   • Use AWS Network ACLs and Security Groups to control traffic
5. Scalability
   • Consider AWS Transit Gateway for multi-VPC and multi-region setups
   • Avoid manual static routes for large environments

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5. Summary Table

Feature	Static Routing	Dynamic Routing (BGP)
Config	Manual	Automatic
Adapt to failures	No	Yes
Complexity	Low	Medium
Best for	Small/simple networks	Large/complex networks, hybrid clouds
AWS Example	VGW static route table	Site-to-Site VPN or Direct Connect with BGP

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✅ Exam Tip:
For the AWS Advanced Networking exam:

• Know how to configure static vs dynamic routes for VPN and Direct Connect.
• Understand BGP route advertisement, ASN numbers, and automatic failover.
• Be familiar with route propagation and Transit Gateway routing tables.
• Be able to choose the right routing method based on network size, complexity, and redundancy requirements.