On Cycles in AS Relationships

TL;DR

This paper investigates the occurrence of cycles in Autonomous System (AS) relationship data, explaining why such cycles appear and addressing questions from users about their presence.

Contribution

It provides an analysis and explanation for the existence of cycles in AS relationship inference data, clarifying a common concern in network topology studies.

Findings

AS relationship cycles are present in inference data.

The paper explains the reasons behind these cycles.

It addresses user questions about cycle occurrences.

Abstract

Several users of our AS relationship inference data (http://www.caida.org/data/active/as-relationships/), released with cs/0604017, asked us why it contained AS relationship cycles, e.g., cases where AS A is a provider of AS B, B is a provider of C, and C is a provider of A, or other cycle types. Having been answering these questions in private communications, we have eventually decided to write down our answers here for future reference.