FIB (Forwarding Information Base)

August 10, 2023
The Forwarding Information Base, known as the FIB, is a critical component of a router or network switch. Basically, it is a table that maps network prefixes to the corresponding next-hop addresses.

This table is used by routers to make operational decisions about where to route a packet next, allowing for faster packet forwarding.

A FIB can be compared to a road map of a city, where destinations (network prefixes) are linked to the fastest routes (next node addresses). Just as a well-planned road map ensures efficient traffic flow, a well-structured FIB ensures efficient forwarding of data packets in the network.

FIB and Routing Information Base (RIB)

To fully understand the concept of FIB, it is necessary to understand its relationship to the Routing Information Base (RIB). Although both bases are critical to packet forwarding, they serve different purposes.

The RIB is like a master blueprint of all possible routes in a network. It contains more detailed information including metrics and policies. On the other hand, FIB is a simplified, optimized version of RIB, containing only the best routes for forwarding packets. It is like an optimized roadmap, stripped of all unnecessary details and focusing only on the fastest routes to each destination.

The role of FIB in packet forwarding

FIB plays a key role in packet forwarding. When a packet arrives at a router, it checks the destination IP address against the FIB. The FIB then provides the next-hop address, which allows the router to quickly forward the packet to the next destination.

This process can be compared to sorting mail. When a package arrives, it checks the destination against its database (FIB) and then quickly sends the package via the fastest route to the destination.

Establishment and maintenance of FIBs

FIB is created and maintained through a process known as routing. Routing protocols such as OSPF (Open Shortest Path First) or BGP (Border Gateway Protocol) collect information about network routes. This information is stored in the RIB. The best routes from the RIB are then selected and inserted into the FIB to speed up packet forwarding.

Maintaining the FIB is a dynamic process. As network conditions change, routes may become unavailable or new, faster routes may become available. To ensure optimal packet forwarding, the FIB must be updated accordingly.

We use cookies to optimize site functionality and give you the best possible experience. To learn more about the cookies we use, please visit our Cookies Policy. By clicking ‘Okay’, you agree to our use of cookies. Learn more.