TCAM architecture for IP lookup using prefix properties

V.C. Ravikumar, R.N. Mahapatra
2004 IEEE Micro  
In modern IP routers, Internet Protocol (IP) lookup forms a bottleneck in packet forwarding because the lookup speed cannot catch up with the increase in link bandwidth. Ternary content-addressable memories (TCAMs) have emerged as viable devices for designing high-throughput forwarding engines on routers. Called ternary because they store don't-care states in addition to 0s and 1s, TCAMs search the data (IP address) in a single clock cycle. Because of this property, TCAMs are particularly
more » ... tive for packet forwarding and classifications. Despite these advantages, large TCAM arrays have high power consumption and lack scalable design schemes, which limit their use. Today's high-density TCAMs consume 12 to 15 W per chip when the entire memory is enabled. To support the superlinearly increasing number of IP prefixes in core routers, vendors use up to eight TCAM chips. Filtering and packet classification would also require additional chips. The high power consumption of using many chips increases cooling costs and also limits the router design to fewer ports. 1 Recently, researchers have proposed a few approaches to reducing power consumption in TCAMs, 1,2 including routing-table compaction. 3,4 Liu presents a novel technique to eliminate redundancies in the routing table. 3 However, this technique takes excessive time for update because it is based on the Espresso-II minimization algorithm, 5 which exponentially increases in complexity with the number of prefixes in a routing table. Thus, our work's main objective is a TCAM-based router architecture that consumes less power and is suitable for the incremental updating that modern IP routers need. Additionally, the approach we will describe minimizes the memory size required for storing the prefixes. We propose a two-level pipelined architecture that reduces power consumption through memory compaction and the selective enablement of only a portion of the TCAM array. We also introduce the idea of prefix aggregation and prefix expansion to reduce the number of routing-table entries in TCAMs for IP lookup. Today, TCAM vendors provide mechanisms to enable a chunk of TCAM much smaller than the entire TCAM array. Exploiting this technology reduces power consumption during lookup in the TCAM-based router. We also discuss an efficient incremental update scheme for the routing of prefixes and provide empirical equations for estimating memory requirements and proportional power consumption for the proposed architecture. Finally, we use traces from bbnplanet, attcanada, utah, and is routers to validate the proposed TCAM architecture's effectiveness. Background and related work
doi:10.1109/mm.2004.1289292 fatcat:lwuwqwymvfee7fbsvrx4gmxbqa