Over the past few months, we announced the support for Geographic Traffic Routing, Fast failover, and TCP probing using Azure Traffic Manager. It is our constant endeavor to add new capabilities that add value to our customers. Today, we are excited to announce the support for EDNS Client Subnet (ECS) in Azure Traffic Manager.

When customers choose to use Performance or Geographic routing methods with Azure Traffic Manager, the routing decision made depends on the origin of the Domain Name System (DNS) request. Azure Traffic Manager determines the request origin region by inspecting the source IP address of the query, which in most cases will be the IP address of the local DNS resolver that does the recursive DNS lookup on behalf of the end user.

While this is a good proxy for the location of the end user, there are many cases where a user can be using a resolver outside of their geographical location. This results in our query response not being optimized.

With the support for ECS, Azure Traffic Manager will use this information, if it is passed by the DNS resolver proxying the query, to make routing decisions. This will result in increased accuracy when Performance routing method is used and increased correctness of geographic location identification if Geographic routing method is used.

Specifically, this feature provides support for RFC 7871 – Client Subnet in DNS Queries that provides an Extension Mechanism for DNS (EDNS0) which can pass on the client subnet address to resolvers.

There is no customer action needed to enable this feature and it is available in all the Azure clouds. All your end user queries with ECS information are already benefitting from this new capability from Azure Traffic Manager!