While the performance characteristics of access networks
and end-user-to-server paths are well-studied, measuring the
performance of the Internet's core remains, largely, an uncharted
territory. With more content being moved closer to
the end-user, server-to-server paths have increased in length
and have a significant role in dictating the quality of services
offered by content and service providers. In this paper,
we present a large-scale study of the effects of routing
changes and congestion on the end-to-end latencies of
server-to-server paths in the core of the Internet.
We exploit the distributed platform of a large content delivery network, composed of thousands of servers around the globe, to assess the performance characteristics of the Internet's core. We conduct measurement campaigns between thousands of server pairs, in both forward and reverse directions, and analyze the performance characteristics of server-to-server paths over both long durations (months) and short durations (hours). Our analyses show that there is a large variation in the frequency of routing changes. While routing changes typically have marginal or no impact on the end-to-end round-trip times (RTTs), 20% of them impact IPv4 (IPv6) paths by at least 26 ms (31 ms). We highlight how dual-stack servers can be utilized to reduce server-toserver latencies by up to 50 ms. Our results indicate that significant daily oscillations in end-to-end RTTs of serverto-server paths is not the norm, but does occur, and, in most cases, contributes about a 20 ms increase in server-toserver path latencies.