Netgear XCM8810 Chassis User Manual - Page 610

NETGEAR 8800 User Manual ECMP table entry, so duplicate gateway sets require additional ECMP table entries, which reduces the total number of gateway sets the ECMP table can support. This approach also limits the total number of LPM table entries that can use IP route sharing to the total number of ECMP table entries. The ECMP table is smaller than the LPM table, so IP route sharing is not available to all LPM table entries on these platforms. For improved ECMP scaling, each LPM table entry points to a gateway set entry in the ECMP table: Each gateway set entry for the platforms listed above is unique and appears only once in the ECMP table. Multiple LPM table entries can point to the same gateway set entry. This efficient use of the ECMP table creates more room in the ECMP table for additional gateway set entries. It also makes IP route sharing available to every entry in the LPM table. The following command allows you to configure the maximum number of next-hop gateways for gateway sets in the ECMP table: configure iproute sharing max-gateways Each gateway entry in a gateway set consumes ECMP table space. As the max_gateways value decreases, the ECMP table supports more gateway sets. If you configure the max_gateways value to 8, the switch supports route sharing through up to 8 gateways per subnet, but supports the smallest number of gateway sets. If you do not need to support up to 8 different gateways for any subnet, you can decrease the max_gateways value to support more gateway sets. To determine which gateways might be added to the ECMP table, consider how many local gateways are connected to the switch and can be used for ECMP, and consider the max_gateways value. For example, suppose that you have four ECMP gateway candidates connected to the switch (labeled A, B, C, and D for this example) and the max_gateways option is set to 4. For platforms that allow a gateway set entry to support multiple subnets, this configuration could result in up to 11 gateway sets in the ECMP table: ABCD, ABC, ABD, ACD, BCD, AB, AC, AD, BC, BD, and CD. If there are 4 gateways and you set max-gateways to 4, you can use the choose function to calculate the total number of gateway set possibilities as follows: (4 choose 4) + (4 choose 3) + (4 choose 2) = 11 To calculate the number of gateway set possibilities for a given number of total gateways and a specific max-gateways value, use the choose function in the following formula: (TGW choose MGW) + (TGW choose MGW-1) + ... + (TGW choose 2) = TGWsets In the formula above, TGW represents the total local gateways, MGW represents the max_gateways value, and TGWsets represents the total gateway sets needed to support all possible shared paths. To see if your platform supports the total gateway sets needed, do the following: • Calculate the total ECMP gateway sets possible as described above. • Compare your result to the IP route sharing (total combinations of gateway sets) capacities listed in the XCM8800 Release Notes to verify that the switch can support the desired number of gateway sets. 610 | Chapter 20. IPv4 Unicast Routing