Industry-standard routing protocols that are used in AWS hybrid networks(for example, BGP over Direct Connect)

Task Statement 3.1: Maintain routing and connectivity on AWS and hybrid networks.

📘AWS Certified Advanced Networking – Specialty

In AWS, hybrid networks connect on-premises data centers to AWS cloud environments. Maintaining proper routing and connectivity is crucial so that resources in AWS can communicate with on-premises systems and vice versa.

1. What Are Routing Protocols?

Routing protocols are rules or methods that network devices use to share information about network paths.
They determine the best path for data to travel across networks.
In hybrid networks, routing protocols ensure that AWS and on-premises networks see each other’s routes correctly.

2. Industry-Standard Routing Protocols in AWS Hybrid Networks

The most important routing protocols you need to know for AWS hybrid networks are:

a) BGP (Border Gateway Protocol)

Type: Exterior Gateway Protocol (EGP)
Purpose: BGP connects different networks together. In AWS, this means connecting your on-premises network to your AWS VPCs.
Usage in AWS:
- Commonly used over AWS Direct Connect or VPN connections.
- It allows dynamic routing, meaning routes are automatically shared and updated between AWS and on-premises.
- Helps with high availability and redundancy, because BGP can choose alternative paths if one fails.

How BGP Works in AWS Hybrid Networks

You have a Direct Connect link from your on-premises network to AWS.
On your AWS side, you create a Virtual Private Gateway (VGW).
BGP sessions are established between your on-premises router and the VGW.
Routes (IP prefixes) are exchanged automatically. Example:
- On-premises: 10.0.0.0/16
- AWS VPC: 172.31.0.0/16
BGP ensures that traffic destined for AWS knows the best path via Direct Connect.

Exam Tip: Know the Autonomous System Number (ASN) concept. BGP uses ASNs to identify networks:

On-premises network has an ASN (private or public)
AWS VGW also has an ASN (default is 64512, but can be customized)
BGP uses ASNs to prevent routing loops.

b) Static Routing (optional but useful)

Type: Manual routing
Routes are manually added rather than exchanged dynamically.
Useful for VPN connections or when BGP is not required.
Limitation: If the network changes, you must update routes manually. This makes it less flexible than BGP.

c) OSPF (Open Shortest Path First) and EIGRP

These are internal routing protocols (Interior Gateway Protocols or IGPs) used inside an enterprise network.
AWS does not natively support OSPF or EIGRP on the VPC side.
They are mostly used inside on-premises networks and can connect to AWS using BGP as a bridge.
Key idea: OSPF/EIGRP manage internal paths, BGP manages paths between networks.

3. Why BGP is Preferred for AWS Hybrid Networks

Feature	BGP	Static Routing
Automation	✅ Dynamically learns routes	❌ Manual updates needed
Scalability	✅ Supports large networks	❌ Hard to scale
Redundancy	✅ Can reroute traffic automatically	❌ Manual intervention required
AWS Support	✅ Fully supported with Direct Connect & VPN	✅ Only for simple connections

4. AWS Services Supporting Hybrid Routing

AWS Direct Connect
- Dedicated connection between on-premises and AWS
- Supports BGP dynamic routing
- Allows private VIF for VPC connectivity
AWS VPN
- Encrypted connection over the Internet
- Supports BGP dynamic routing or static routing
- Often used as a backup for Direct Connect
Virtual Private Gateway (VGW)
- AWS side of a hybrid network connection
- Works with BGP to exchange routes dynamically
Transit Gateway
- Connects multiple VPCs and on-premises networks
- Supports BGP with multiple Direct Connect or VPN connections

5. Key BGP Concepts for the Exam

Autonomous System (AS): Unique number identifying a network. AWS default AS = 64512.
BGP Peering: Establishing a session between AWS and on-premises router to exchange routes.
Prefixes: IP ranges exchanged via BGP (example: 10.0.0.0/16).
Route Propagation: VGW or Transit Gateway automatically shares routes to VPC route tables.
Failover: BGP automatically chooses a backup path if the main path fails.

Exam Tip: Understand BGP path selection criteria, such as:

Highest weight (on-premises specific)
Shortest AS path
Lowest origin type
Lowest MED (Multi-Exit Discriminator)
eBGP over iBGP

6. Example Scenario in IT Terms

You have Data Center A with 10.0.0.0/16 and AWS VPC with 172.31.0.0/16.
You establish Direct Connect.
Configure BGP session between Data Center Router and AWS VGW.
Data Center learns AWS routes automatically.
AWS learns on-premises routes automatically.
If Direct Connect fails, traffic can reroute via VPN, ensuring connectivity continuity.

7. Summary for Exam

BGP is the standard routing protocol for AWS hybrid networks.
Dynamic routing is preferred over static routing for scalability and redundancy.
Key AWS services: Direct Connect, VPN, VGW, Transit Gateway.
Understand ASNs, BGP peering, prefixes, and failover.
Know the difference between internal protocols (OSPF/EIGRP) and external protocols (BGP).

✅ Quick Exam Tips:

Always assume BGP is used for hybrid networks unless static routing is explicitly mentioned.
Direct Connect + BGP is high bandwidth, low latency, and reliable.
Static routing can be used for simple VPN setups, but BGP handles complex networks better.