Efficient multi-match packet classification with TCAM

Today's packet classification systems are designed to provide the highest priority matching result, e.g., the longest prefix match, even if a packet matches multiple classification rules. However, new network applications, such as intrusion detection systems, require information about all the matching results. We call this the multi-match classification problem. In several complex network applications, multi-match classification is immediately followed by other processing dependent on the classification results. Therefore, classification should be even faster than the line rate. Pure software solutions cannot be used due to their slow speeds. We present a solution based on ternary content addressable memory (TCAM), which produces multi-match classification results with only one TCAM lookup and one SRAM lookup per packet - about ten times fewer memory lookups than a pure software approach. In addition, we present a scheme to remove the negation format in rule sets, which can save up to 95% of TCAM space compared with the straight forward solution. We show that using our pre-processing scheme, header processing for the SNORT rule set can be done with one TCAM and one SRAM lookup using a 135 KB TCAM.