Note: Latency between hosts on the internet can change over time due to changes in network connectivity and routing.

Clients with support for EDNS0-Client-Subnet

If the resolver supports EDNS0-Client-Subnet, the client DNS queries might exit from a different location than the client location and result in unexpected routing behavior.

Change where the client DNS queries exit to a location geographically closer to the client.

Clients without support for EDNS0-Client-Subnet

If the resolver doesn't support EDNS0-Client-Subnet, the client DNS queries might use a DNS resolver in a different geographic location from the client and result in unexpected routing behavior.

Change the DNS resolver that the client uses to a different recursive DNS resolver located geographically closer to the client.

Optional: If the DNS resolver doesn't support EDNS0-Client-Subnet and Route 53 routes users to suboptimal Regions as a result, switch to a public recursive DNS resolver that supports EDNS0-Client-Subnet. Then, compare your old latency routing response results from Route 53 with your new results. Some public DNS resolvers that currently support EDNS0-Client-Subnet are GoogleDNS (8.8.8.8 and 8.8.4.4) and OpenDNS (208.67.222.222 and 208.67.220.220).

Troubleshooting example

A company has latency-based routing records for two Elastic Load Balancers located in Virginia (us-east-1) and Ireland (eu-west-1). Users in the USA use a corporate DNS resolver located in Europe, or connect to the corporate office in Europe over VPN.

If the corporate DNS resolver isn't capable of sending EDNS0-Client-Subnet data (truncated client IP address information) to the authoritative name servers, Route 53 considers the DNS resolver IP address in Europe to be the source of the query. Route 53 then performs a lookup in its latency database and incorrectly determines that the load balancer in Ireland has the lowest latency.

However, if the corporate DNS resolver is capable of sending EDNS0-Client-Subnet data, Route 53 considers the truncated client IP in the USA as the source of the DNS query. Route 53 then performs a lookup in its latency database and correctly determines that the load balancer in Virginia has the lowest latency.