  Colocation facilities and Internet eXchange Points (IXPs) provide neutral
places for concurrent networks to daily exchange terabytes of data traffic.
Although very reliable, these facilities are not immune to failure and may
experience difficulties that can have significant impacts on exchanged traffic.
In this paper we devise a methodology to identify collocation facilities in
traceroute data and to monitor delay and routing patterns between facilities.
We also present an anomaly detection technique to report abnormal traffic
changes usually due to facilities outages. We evaluate this method with eight
months of traceroute data from the RIPE Atlas measurement platform and manually
inspect the most prominent events, that are: an IXP outage, a DDoS attack, and
a power failure in a facility. These case studies validate the benefits of the
proposed system to detect real world outages from traceroute data. We also
investigate the impact of anomalies at the metropolitan-level and identify
outages that span across up to eight facilities.
