The Circuit Breaker That Cried Wolf: Measuring BGP Maximum-Prefix Exceedance and Connectivity Impact

Abstract

The BGP maximum-prefix limit serves as a network circuit breaker, tearing down sessions when announcements exceed a configured threshold. Despite its operational significance, little is known empirically about how accurately these limits reflect reality, how often they are exceeded, or what connectivity impact results from their exceedance. We present a first large-scale measurement study of BGP maximum-prefix limits in the wild, combining 12 months of RIPE RIS snapshots with PeeringDB metadata and CAIDA AS Rank data. Only 32.49% of RIS-visible ASes appear in PeeringDB, and 21--27% of recent limit fields carry a value of zero, indicating no declared limit; after filtering for recency and non-zero limits, 14,973 ASes form our analytical dataset. Among these, 14.55% (IPv4) and 11.24% (IPv6) exceed their declared limit intermittently, and 2.15% and 2.32% do so in every observed snapshot. These exceedances are driven by organic growth, such as new space acquisition or deaggregation, yet the mechanism responds identically to a route leak: Tier-1 and Major peers account for 18.4% of IPv4 lost sessions despite representing roughly 0.1% of all ASes. Based on our findings, we offer recommendations for operators and IXPs and call for renewed IETF standardization of dynamic limit negotiation.