Consistent TCAM Policy Table Update with Zero Impact on Data Path Processing

Using Ternary Content Addressable Memory (TCAM) for general policy filtering has been gaining popularity due to TCAM’s deterministic and fast lookup performance. However, the policy table updating poses significant challenge for efficient use of TCAM for policy filtering. To avoid erroneous and inconsistent rule matching while a policy table is being updated, the traditional wisdom is to lock the policy table during the rule update period. This, however, can negatively impact the data path processing. In this paper, we put forward a Consistent Policy Table Update Algorithm (CPTUA) for TCAM. Instead of attempting to minimize the number of rule movements to reduce the locking time, CPTUA maintains a consistent policy table throughout the table updating process, thus eliminating the need for locking the policy table while ensuring the correctness of the rule matching. Our analysis shows that even for a policy table with 1 million rules, arbitrary number of rules can be updated simultaneously in subseconds in the worst case, provided that 15% of the policy table entries are empty. This implies that with CPTUA, any new rule can be enforced in subseconds for any practical policy table sizes with zero impact on the data path processing.