Using forgetful routing to control BGP table size

Running the Border Gateway Protocol (BGP), the Internet's interdomain routing protocol, consumes a large amount of memory. A BGP-speaking router typically stores one or more routes, each with multiple attributes, for more than 170,000 address blocks, and growing. When the router does not have enough memory to store a new route, it may crash or enter into other unspecified behavior, causing serious disruptions for the data traffic. In this paper, we propose a new mechanism for routers to handle memory limitations without modifying the underlying routing protocol and without negatively affecting convergence delay. Upon running out of memory, the router simply discards information about some alternate routes, and requests a "refresh" from its neighbors later if necessary. We present an optimal offline algorithm for deciding which alternate routes to evict, and explore the trade-off between memory size and refresh overhead using a large BGP message trace. Based on these promising results, we design and evaluate efficient online algorithms that achieve most of the performance benefits. We believe that our scheme can significantly improve the scalability and robustness of IP routers in the future.