Mapping XConnects

XConnect (cross connect) is a private link between two tennants of a data center.


Companies like Equinix, CoreSite, and Telx manage and operate carrier-neutral colocation facilities (also called colos) where they provide, among other offerings, interconnection services. These facilities supply the infrastructure (e.g., rack space, cabling, power, and physical security) necessary for network operators to colocate their routers for easy interconnection. This work focuses on identifying interconnections of the "cross connect" type, i.e., dedicated point-to-point private peering links (which might be used to carry transit traffic or peer-to-peer traffic) that the network operators can buy from the colo providers so that their networks can exchange traffic within the confines of these facilities. In particular, our goal is to infer who is interconnecting with whom in which colos in which cities. Precisely locating the private peering links between two networks is a prerequisite for studying, for example, the root causes of the peering disputes between large content and eyeball providers in recent years.

XConnects in a Commercial Colo Facility

In order to demonstrate the capabilities of our approach, we report on the initial results of our research with the goal of mapping xconnects in commercial colocation facilities. In particular, we present case studies involving a colocation facility in Seattle, WA, and another in Chicago, IL, both of which are owned and operated by the Zayo Group. The Seattle facility is located in the Westin building, the premier carrier hotel in Seattle, with close proximity to numerous trans-Pacific cable landing stations in the Seattle area. Each of the two facilities has some 20 tenants and their names are published on Zayo’s website. Following is a set of visualizations aiming at showing the results of our mapping in both colos. For a detailed description of approach please see our technical report.

Seattle Colocation | 2001 6th | Zayo Group

Chicago Colocation | 600 S Federal | Zayo Group

How to Read the Graphs

In AS-level graphs, we use dark blue to show the ASes with at least one interface pinned to the target colo. Light green shows Tier-1 ASes that are localized to another close-by facility and yellow is used for the remaining ASes. Cross connects that are mapped to the target colo are shown as thick edges, and cross connects that result from connectivity options provided by the zColo facility and are localized to a close-by colo are indicated by dashed lines. For the remaining edges, we have insufficient evidence to localize them to the inside or outside of zColo.

XConnect level graphs show physical connectivity of inter AS links between the tenants of each colo facility in each city. Three types of nodes are represented in each graph. PoP-tags (e.g., AS6461:ABOVE_SEA1) represent location information that can be extracted from PTR records assinged by an AS. Interface node (e.g., represet interfaces right at the border of tenant ASes. If the PTR record of an interface contains certain PoP tag, it would be connected to that specific PoP tag. Finally router nodes represent alias relationship between two or more interfaces. Node colors represnt different ASes. Interfaces represented by stars are pinned to the facility and similarly a PoP tag node represnted by a cylinder. The color of links shows the indirect delay of the physical link measured by traceroutes, where delay below 3ms is represented by green and delay above 20ms by red links.

Reza Motamedi
University of Oregon

Balakrishnan Chandrasekaran
Duke University

Bruce Maggs
Duke University / Akamai

Reza Rejaie
University of Oregon

Walter Willinger
Niksun, Inc.