BGP Prefix Delegations: A Deep Dive.

ABSTRACTAmong the scalability limits in the Internet routing ecosystem are the BGP routing table size and the rate of updates. In this paper, we focus on the former. The BGP routing table size has been growing superlinearly in the past decades. Although the address space allocation was structured with aggregation in mind, this capability is impaired due in part to the need for traffic engineering. One major impairment are delegated prefixes. Prefix delegations contribute 15% to the routing table size and they also involve 14% of the traffic. Moreover, they reflect the large complexity of BGP: Delegations are not only the results of providers delegating address space to their customers but also vice versa. Some delegations are due to load balancing and transitive business relationships, others due to operational practices within organizations. We analyze BGP data as well as large-scale traceroute data to understand how delegations affect path selection. Although the need for delegations is apparent, our work highlights that the fragmentation of address space is going to continue and renders the routing table more and more un-aggregatable.