Number of Flow Set Table Entries

The number of Flow Set table entries used on a LAG (Link Aggregation Group) should be large compared to the number of ports in the aggregator in order to have even distribution when the number of ports in the aggregator is not a power of two. See Example Remapping of Flows where some member ports are assigned 29 flow table entries while others are assigned 28 entries. In this case, assuming equal bandwidth among flows, ports 1 through 4 should be expected to have approximately 3.5% more utilization than ports 5 through 9.

While larger numbers of flow set entries per LAG would improve the evenness of distribution, there are negative tradeoffs involved in the use of large flow tables. The use of a very large number of Flow Set table entries negatively affects the performance of flow remapping during aggregator changes due to the need to calculate membership for a large number of entries and to write these entries to the hardware. Additionally, the use of very large numbers of Flow Set table entries per LAG restricts the number of LAGs on which Resilient Hashing could be enabled. The size of the Flow Set table is 32,768 for use over all LAGs configured to use Resilient Hashing, assuming that both LAG and ECMP require use of the resilient hashing flow set table.

In order to accommodate resilient hashing for switches with large numbers of ports, the number of Flow Set table entries will be set to 32 times the number of ports in the LAG (rounded up to the nearest power of two as required by the hardware). This setting accomodates a switch with 1024 total ports, all of which are configured to use resilient hashing.