Root causes for iBGP routing anomalies

Today, spreading global routing information within an Autonomous System (AS) is usually implemented by means of internal BGP (iBGP), a particular operational mode of the Border Gateway Protocol (BGP). Considering the research activities around BGP, anomalies turned out to be one major issue of iBGP: But even if the trouble iBGP anomalies induce in practice is well known for nearly a decade, new iBGP extensions still define highly problematic protocol modifications. Apparently, protocol designers are either not aware of the conceptual defects that induce anomalies or validating correctness appears to be too complex. In this paper, we provide a basis to solve both problems. Focussing the basic correctness properties of routing protocols, we will show that iBGP anomalies are caused by five root causes. These causes provide protocol designers with a tool set to reveal problematic properties of a concept and verify correctness. Based on exemplary studies for two common iBGP architectures, we will provide detailed guidance for practical usage.