Reserves storage space for IPv4 and IPv6 routes in the Longest Prefix Match (LPM) hardware tables, allowing individual local and remote IPv4 unicast hosts to occupy the unused portions of the tables.
| num_routes_needed | Specifies a specific number of routes to reserve. |
| maximum | Reserves the maximum amount of space for IP route entries. No IPv4 hosts are stored in the LPM and External tables. |
| default | Reserves the default amount of space for IP route entries. |
| all | For SummitStack switches only, this option applies the reservation to all applicable slots. |
| slot_num | For SummitStack switches only, this option applies the reservation to the specified slot. |
Demand on the Layer 3 Hash table can be reduced by allowing IPv4 hosts to be stored in the LPM tables instead. This command allows you to reserve a portion of the LPM tables for routes, and this creates an unreserved portion that can be used to store IPv4 hosts. For more information, see the “Extended IPv4 Host Cache” section of the Switch Engine 32.3 User Guide .
The default setting can support most networks, but if more than a few hundred local IP hosts and IP multicast entries are present, you can improve switch performance by calculating and configuring the reserved space for route entries to allow unreserved space for IPv4 hosts. Changing the number of reserved route entries does not require a reboot of the affected slots or switch.
You can view the current LPM hardware table usage by entering the show iproute reserved-entries statistics command. The LPM table statistics are in the columns under the In HW Route Table heading.
If the switch contains fewer routes than the capacity of the LPM tables, the number of route entries to reserve for a slot or switch should be the number of routes currently used in the hardware tables, plus an additional cushion for anticipated growth. Because each IPv6 route takes up the space of two IPv4 routes, the number of route entries to reserve is two times the value in the IPv6 routes column, plus the value in the IPv4 routes column, plus room for anticipated growth. For example, if you want to reserve space for 100 IPv4 routes and 20 IPv6 routes, the required number of route entries is 140 (100 + 2*20).
The maximum value for num_routes_needed for ExtremeSwitching 5420 switches is 12,256. For all other models, 16,352.
The maximum values shown above apply to ExtremeSwitching series switches operating independently or as part of a SummitStack. The maximum option can be used to specify the maximum values.
When maximum is specified, IPv4 hosts do not occupy LPM table space. Note that when maximum is specified, software forwarding can result, depending on the utilization and addresses in the Layer 3 Hash table, and is therefore not recommended.
When Algorithmic Longest-Prefix Match (ALPM) is configured using configure forwarding internal-tables more routes, the value for reserved-entries is treated as "maximum". Therefore, IPv4 hosts do not occupy LPM table space in order to maximize route capacity.
If the switch contains more routes than the capacity of the LPM tables, a trade-off can be made. You can choose to reserve 400 iproute entries, for example. The 400 IPv4 routes with the longest length network masks will be installed in the LPM table, and the remainder of the LPM table can be used for cache space for local and remote hosts. The remote host entries are only required for IPv4 addresses matching one of the 300 routes not installed in the LPM table. Since in this example, not all routes can be stored anyway, leaving appropriate room for individual remote hosts can result in more fast-path forwarding.
Depending on the actual routes present, IP route compression for IPv4 and/or IPv6 can be enabled to reduce the number of routes required in the LPM tables. For more information, see the description for the following command: enable iproute compression {vr vrname}
The following command reserves up to 140 IPv4 routes or 70 IPv6 routes, or any combination in between, on all switches in a SummitStack:
# configure iproute reserved-entries 140 slot all
For details on the configuration changes, see the command descriptions for the following commands:
This command was first available in ExtremeXOS 12.1.
This command is available on ExtremeSwitching 5320, 5420, 5520, and 5720 series switches.