Low - Fragmentation mapping strategies for linear forwarding tables in infinibandTM*

Abstract

The InfiniBand Architecture (IBA) supports distributed routing by using forwarding tables stored in each switch, which only consider the destination local identifier (LID) of the packet for routing. Each LID is mapped to a different table entry. Additionally, the IBA specifications allow each destination port to be assigned up to 2n consecutive virtual addresses by masking the n least significant bits of its LID. Each range of virtual addresses must be mapped to consecutive table entries when IBA linear forwarding tables are used. However, the fact that each port may require a different number of virtual addresses and the fact that this number may not be a power of two could lead to waste some table entries, causing a fragmentation of the forwarding tables as a consequence of an inefficient mapping strategy of LIDs. Fragmentation of the forwarding tables could become critical as far as it reduces the number of available table entries to map LIDs, limiting, in turn, the number of ports that can be placed in the network. In this paper, we propose two effective mapping strategies to tackle the fragmentation effect on IBA forwarding tables. The first strategy is able to remove the fragmentation effect when the number of virtual addresses is a power of two for all destinations, introducing a fragmentation percentage lower than 20% in all cases. On the other hand, the second strategy is able to almost completely eliminate the possible fragmentation effect. © Springer - Verlag 2003.