1.1.b Identify Cisco express forwarding concepts

1.1.b [i] RIB, FIB, LFIB, Adjacency table

Routing Information Base (RIB)

RIBs (Routing Information Base) maintain the network topologies and routing tables for each protocol. This would include many routes going to the same destination prefix. It is built on per routing protocol basis, so RIP and OSPF have their own copy of RIBs.

Forwarding Information Base (FIB)

FIBs are the best routes from possibly many routing protocols in the RIBs pushed down to fast forwarding lookup memory (or just DRAM for software-based platforms) for the best path( s). This is what you see in show ip route command output. There is one copy of FIB per system for centralized forwarding platforms, or one for each line card in case of distributed systems.

Label Information Base (LIB)

LIB (Label Information Base ) is the software table maintained by IP/ MPLS capable routers to store the details of port and the corresponding MPLS router label to be popped or pushed on incoming or outgoing MPLS packets respectively. LIB entries are populated from label-distribution protocols. LIB functions in the control plane of Cisco routers. It is used by the label distribution protocol for mapping the next hop labels.

Label forwarding information base (LFIB) is a data structure and way of managing forwarding in which destinations and incoming labels are associated with outgoing interfaces and labels. The forwarding paradigm employed by MPLS is based on the notion of label swapping. When a packet with a label is received by an Label Switching Router (LSR), the switch uses the label as an index in its LFIB to determine the outgoing interface.

Adjacency Tables

Routers or Switches in a network are considered adjacent if they can reach each other with a single hop across a link layer. In addition to the FIB, CEF uses adjacency tables to prepend Layer 2 addressing information such as MAC addresses. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 891-894).  . Kindle Edition.