Hot Potatoes Heat Up BGP Routing

The separation of intradomain and interdomain routing is a key feature of the Internet routing architecture. However, intradomain routing protocols such as OSPF and IS-IS do have a (sometimes significant) influence on the path-selection process in Border Gateway Protocol (BGP). In this paper, we argue that researchers should revisit the “interface” between the two tiers of the Internet routing system. Toward this end, we present an initial analysis of the impact of OSPF on BGP in a large ISP network. We propose a general methodology for associating BGP update messages with events visible in OSPF. Then, we apply our methodology to streams of OSPF link-state advertisements and BGP update messages. Our analysis shows that (i) “hot potato” routing is sometimes a significant source of BGP updates, (ii) BGP updates can lag seconds behind the related OSPF event, which can cause delays in forwarding-plane convergence, (iii) OSPF-triggered BGP updates have a nearly uniform distribution across destination prefixes, and (iv) the fraction of BGP messages triggered by OSPF varies significantly across time and router locations, with important implications on external monitoring of BGP. Our measurement methodology and analysis results represent an important step in understanding the interplay between intradomain and interdomain routing.