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Packet Classification using Tuple Space SearchV. Srinivasan,S. Suri, and G. Varghese Routers must perform packet classification at high speeds to efficiently implement functions such as firewalls and QoS routing. Packet classification requires matching each packet against a database of filters (or rules), and forwarding the packet according to the highest priority filter. Existing filter schemes with fast lookup time do not scale to large filter databases. Other more scalable schemes work for 2-dimensional filters, but their lookup times degrade quickly with each additional dimension. While there exist good hardware solutions, our new schemes are geared towards software implementation. We introduce a generic packet classification algorithm, called Tuple Space Search (TSS). Because real databases typically use only a small number of distinct field lengths, by mapping filters to tuples even a simple linear search of the tuple space can provide significant speedup over naive linear search over the filters. Each tuple is maintained as a hash table that can be searched in one memory access. We then introduce techniques for further refining the search of the tuple space, and demonstrate their effectiveness on some firewall databases. For example, a real database of 278 filters had a tuple space of 41 which our algorithm prunes to 11 tuples. Even as we increased the filter database size from 1K to 100K (using a random two-dimensional filter generation model), the number of tuples grew from 53 to only 186, and the pruned tuples only grew from 1 to 4. Our Pruned Tuple Space search is also the only scheme known to us that allows fast updates and fast search times. We also show a lower bound on the general tuple space search problem, and describe an optimal algorithm, called Rectangle Search, for two-dimensional filters. For information about joining SIGCOMM, follow this link The referenced paper appears in Computer Communication Review, a publication of ACM SIGCOMM, volume 29, number 4, October 1999. ACM Copyright Notice: Copyright (c) 1999 by Association for Computing Machinery, Inc. (ACM) Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that the copies are not made or distributed for profit or commercial advantage and that the copies bear this notice and full citation on the first page. Copyright for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permission to publish from: Publications Dept. ACM, Inc. Fax +1 212 869 0481 or email at mailto:permission@acm.org |