Which conceptual table created by routing protocols is used when processing an IP packet?

The Forwarding Information Base (FIB), also known as a forwarding table, is the specific data structure used by a router's data plane to make forwarding decisions for IP packets. While routing protocols (operating in the control plane) populate a Routing Information Base (RIB) with all known routes, the FIB is a streamlined, optimized version containing only the best, unambiguous routes. This optimization allows for the extremely fast lookups required for line-rate packet processing. When a packet arrives, its destination IP address is looked up in the FIB to determine the next-hop and egress interface.

A. The Management Information Base (MIB) is used by network management protocols like SNMP for monitoring and configuration, not for per-packet forwarding decisions.

B. The Label Information Base (LIB) is used in MPLS networks to map labels to next-hop label forwarding entries, specifically for forwarding labeled packets.

C. The Traffic Engineering Data Base (TED) is a control plane database used by protocols like OSPF-TE to calculate constrained paths, not for direct packet forwarding.

1. IETF RFC 3222: Terminology for Forwarding Information Base (FIB) based Router Performance. Section 2

"Definitions

" states: "The Forwarding Information Base (FIB) is a data structure that is used to make forwarding decisions... It is populated with information from the Routing Information Base (RIB)."

2. Stallings

W. (2017). Data and Computer Communications (10th ed.). Pearson. In Chapter 19

"Routing

" the distinction is made clear: "The routing protocol populates a routing table (or RIB)... From the RIB

a forwarding table (or FIB) is created

which is used to make forwarding decisions." (Paraphrased from concepts in Section 19.2).

3. Kurose

J. F.

& Ross

K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. Chapter 4

Section 4.4

"Inside a Router

" describes the separation of the control plane (routing algorithms building the RIB) and the data plane (forwarding function using the FIB). The forwarding table (FIB) is explicitly identified as the structure consulted during the input port processing for packet forwarding.