Techniques are described for measuring TCP connection quality between a client and a plurality of data centers. A small amount of code, called a web beacon, is placed onto production web pages. When a client requests the production web page, the web page is served to the client. When the web page code is processed, the web beacon instructs the client to retrieve zero-content images from a plurality of data centers through TCP connections in the background. As each connection is made, a passive monitoring system measures and logs statistics about each TCP connection from the client to the data center. The statistics are aggregated into a database and may be sorted based upon ranges of IP addresses of clients and the connection quality measurements. The data is exported from the database to global load balancers to determine routing from subsequent clients to the plurality of data centers.