AZ-700 Question 140
Single answerYour organization has multiple subnets spread across several Azure VNets that connect to on-premises through an ExpressRoute circuit. The on-premises routers are learning many specific routes from Azure, causing increased complexity in the on-premises routing tables. You need to reduce the number of advertised routes on the on-premises side without losing connectivity to any Azure subnets. Which approach should you recommend to achieve route summarization from Azure to on-premises?
- A
Design your VNets with a single aggregated address space so Azure only advertises that summarized prefix to on-premises
- B
Enable forced tunneling on the virtual network gateway to merge all specific routes into a single route
- C
Use the 'Summarize Subnets' feature in the Azure portal to automatically combine all subnet routes into one advertisement
- D
Advertise a default route (0.0.0.0/0) from Azure to on-premises so it only sees one route for all VNets
Show answer and explanation
Correct answer: A
Explanation
Azure automatically advertises the address spaces that you define within your VNets to your on-premises network through ExpressRoute. To minimize the routes advertised, it's best to use a single aggregated CIDR block that encompasses all subnets. This design allows Azure to advertise only the summarized prefix, reducing the routing entries on the on-premises side. For more details, refer to Microsoft documentation on ExpressRoute circuit routing preferences, which outlines how to plan and configure VNet address spaces for efficient route advertisement.
- A. Correct.
Correct. When you provision a VNet with a single aggregated address space (for example, 10.0.0.0/16) that covers all subnets, Azure ExpressRoute advertises only this summarized prefix to on-premises. This reduces the number of routes seen by on-prem devices and simplifies routing.
- B. Incorrect.
Incorrect. Forced tunneling is designed to send all internet-bound traffic from Azure to on-premises, not to summarize routes advertised to the on-prem network. It doesn't reduce the number of Azure subnets advertised to on-prem; it simply affects outbound internet traffic routing.
- C. Incorrect.
Incorrect. There is no built-in 'Summarize Subnets' feature in Azure networking. While you can design your address space to be more aggregated, Azure does not provide a push-button option to auto-combine subnet routes into one advertisement.
- D. Incorrect.
Incorrect. Advertising a default route (0.0.0.0/0) from Azure shifts traffic for all destinations through Azure, which might unintentionally route all on-premises traffic into Azure. This does not properly summarize your existing subnets; it fundamentally changes the default path, which isn�t advisable unless specifically required.