IPv4 FIB LEM optimization

Note: This feature is supported on 7250 IXR Gen 3 platforms.

The 7250 IXR Gen 3 forwarding ASIC supports different types of hardware lookup tables. Some tables are optimized to perform longest-prefix matches, and others are designed for exact-match logic. The exact-match tables are conventionally used for MPLS label lookups and MAC address lookups. When a router is deployed in a role requiring limited exact-match table resources, spare exact-match table capacity can be repurposed to increase IP FIB capacity. SR Linux supports this optimization as a system-wide configuration option. When the optimization is enabled, IPv4 routes with specific prefix lengths (/20, /21, /22, /23, and /24) are programmed into the exact-match tables instead of the longest-prefix match hardware tables, leaving more capacity in these tables for all of the other prefix lengths. This provides a substantial boost to the total IP FIB scale of the system, with benefits increasing as the number of /20-/24 routes increases. The default-free IPv4 Internet routing table has over 1 million routes in 2026, and over 93 percent of these routes are /20-/24 routes.