Caractérisation de la table de routage BGP

International audienceBGP routing table growth is one of the major Internet scaling issues, and prefix deaggregation is thought to be a major contributor to table growth. In this work we quantify the fragmentation of the routing table by the type of IP prefix. We observe that the proportion of deaggregated prefixes has quasi doubled in the last fifteen years. Our study also shows that the deaggregated prefixes are the least stable; they appear and disappear more frequently. While we can not see significant differences in path prepending between the categories, deaggregated prefixes do tend to be announced more selectively, indicating traffic engineering. We find cases where lonely prefixes are actually deaggregation in disguise. Indeed, some large transit ISPs advertise many lonely prefixes when they own the covering prefix. We show the extents of this practice that has a negative impact on the routing table even though it could usually be avoided.La croissance de la table de routage BGP est un des problèmes majeurs de l'expansion d'Internet, et la désaggrégation des préfixes semble être la cause principale de cette croissance. Dans cet article, nous quantifions la fragmentation de la table de routage BGP en classant les préfixes IP par type. Nous observons que la proportion de préfixes désaggrégés a doublé dans les quinze dernières années. Nous montrons également que ces préfixes sont les moins stables: ils apparaissent et disparaissent plus fréquemment. Malgrés le taux similaire de path prepending pour les différentes catégories de préfixes, les préfixes désaggrégés ont tendance à être annoncés sélectivement, indiquant de l'ingénierie de trafic. Une partie des préfixes solitaires sont en réalité désaggrégés. En effet, certains grands FAI annoncent un grand nombre de préfixes solitaires alors qu'ils possèdent le préfixe les couvrant. Nous dévoilons l'étendue de cette pratique qui a un effet non négligeable sur la fragmentation de la table de routage alors qu'elle pourrait généralement être évitée

Distributed Route Aggregation on the Global Network

The Internet routing system faces serious scalability challenges, due to the growing number of IP prefixes it needs to propagate throughout the network. For example, the Internet suffered significant outages in August 2014 when the number of globally routable prefixes went past 512K, the default size of the forwarding tables in many older routers. Although IP prefixes are assigned hierarchically, and roughly align with geographic regions, today's Border Gateway Protocol (BGP) and operational practices do not exploit opportunities to aggregate routes. We present a distributed route-aggregation technique (called DRAGON) where nodes analyze BGP routes across different prefixes to determine which of them can be filtered while respecting the routing policies for forwarding data-packets. DRAGON works with BGP, can be deployed incrementally, and offers incentives for ASs to upgrade their router software. We present a theoretical model of route-aggregation, and the design and analysis of DRAGON. Our experiments with realistic assignments of IP prefixes, network topologies, and routing policies show that DRAGON reduces the number of prefixes in each AS by about 80% and significantly curtails the number of routes exchanged during transient periods of convergence