Overview
Explains selective Forwarding Information Base (FIB) download and provides instructions for configuring selective FIB download to optimize memory and processing efficiency on network devices.
A selective FIB download is a routing optimization feature that
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selectively installs specific destination routes in the Forwarding Information Base (FIB) rather than all available routes
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prevents traffic drops and black holes by ensuring traffic follows default routes when specific destination routes are unavailable, and
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improves network reliability in multi-data center environments by adapting installed routes to current topology and failures.
| Feature Name |
Release Information |
Feature Description |
|---|---|---|
| Selective FIB Download |
Release 26.1.1 | Introduced in this release on: Centralized Systems (8400 [ASIC: K100])(select variants only*) * This feature is now supported on Cisco 8404-SYS-D routers. |
| Selective FIB Download |
Release 25.4.1 | Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*) *This feature is now supported on:
|
| Selective FIB Download |
Release 25.1.1 | Introduced in this release on: Fixed Systems (8700 [ASIC: K100], 8010 [ASIC: A100])(select variants only*) *This feature is supported on:
|
| Selective FIB Download |
Release 24.4.1 | Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100])(select variants only*); Modular Systems (8800 [LC ASIC: P100])(select variants only*) You can now selectively download BGP prefixes to the Routing Information Base (RIB) and Forwarding Information Base (FIB). This feature prevents traffic drops by ensuring that traffic follows default routes when specific destination routes are unavailable. *This feature is supported on:
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Network challenges in multi-data center environments
In multi-data center networks, links or connections between intermediate distribution facilities (IDFs) and their termination points may occasionally fail. When these connections are unavailable, affected IDFs lose precise routing paths to target destinations, complicating traffic management and potentially disrupting service delivery.
Importance of aggregate routes in traffic management
To manage traffic efficiently, a main routing node distributes it across available paths using aggregate routes. An aggregate route is an aggregated network prefix representing multiple destinations within a specific network layer. Intermediate nodes rely on these aggregate routes to forward traffic toward the appropriate IDFs, based on network availability and routing policies.
Risks of traditional routing with missing specific routes
When traffic arrives at an IDF that lacks specific destination routes, the presence of aggregate routes on that IDF can misdirect traffic to a null interface. This situation creates a “black hole,” where data packets are silently discarded, resulting in network connectivity problems and traffic loss.
Benefits of selective FIB download as a solution
Selective FIB download addresses these issues by preventing the installation of aggregate routes in the Routing Information Base (RIB) on local and connected intermediate nodes when direct routes to specific destinations are unavailable. Instead, the network relies on default routes to forward traffic toward alternative nodes that do possess the required specific routes. This approach ensures that traffic is intelligently rerouted through operational parts of the network, ultimately reaching its intended destination and avoiding black holes.
Address-family support
Selective FIB download supports IPv4 unicast and IPv6 unicast prefixes under the default VRF.