Stable and Flexible iBGP

Ashley Flavel and Matthew Roughan
Appears in: 
CCR October 2009

Routing oscillation is highly detrimental. It can decrease performance and lead to a high level of update churn placing unnecessary workload on router the problem is distributed between many providers. However, iBGP — the routing protocol used to distribute routes inside a single Autonomous System —has also been shown to oscillate. Despite the fact that iBGP is configured by a single provider according to apparently straight forward rules, more than eight years of research has not solved the problem of iBGP oscillation. Various solutions have been proposed but they all lack critical features: either they are complicated to implement, restrict routing flexibility, or lack guarantees of stability. In this paper we propose a very simple adaptation to the BGP decision process. Despite its simplicity and negligible cost we prove algebraically that it prevents iBGP oscillation. We extend the idea to provide routing flexibility, such as respecting the MED attribute, without sacrificing network stability.