Amazon Transit Gateway Network Manager provides centralized monitoring and visibility for a global network, including hybrid connectivity over AWS Direct Connect. It generates events for network changes, including BGP routing updates. When a new route is advertised from on-premises, Network Manager emits an event to Amazon EventBridge. An EventBridge rule can be configured to match this specific event and trigger a target, such as an Amazon SNS topic, to send a notification. This creates an efficient, event-driven architecture that directly addresses the requirement for real-time notifications on route changes.

A. Amazon CloudWatch metrics for Direct Connect track connection health, data throughput, and BGP session state, but not the advertisement of individual routes.

C. A Lambda function would have to periodically poll the route tables and compare states. This is an inefficient, complex, and non-real-time polling approach.

D. There is no native feature to enable Amazon CloudWatch Logs on a Direct Connect transit VIF to capture BGP route advertisements.

1. AWS Transit Gateway User Guide, Network Manager, Monitoring your global network with Events: "Network Manager generates events for changes to the network topology, routing, and connection status. Events are delivered to Amazon EventBridge (formerly Amazon CloudWatch Events)... For example, you can create an event to be notified when a BGP route is learned or no longer advertised from a specific BGP peer."

2. Amazon EventBridge User Guide, Events from AWS services, Network Manager events: This section details the event patterns generated by Network Manager that can be used to trigger rules in EventBridge. The aws.networkmanager source provides events for routing updates.

3. AWS Direct Connect User Guide, Monitoring, Monitoring with Amazon CloudWatch: This page lists the available metrics for Direct Connect connections and virtual interfaces. The list includes metrics like ConnectionState and BGPPeeringState but lacks any metric for tracking the number or content of advertised routes.