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352-001 · Question #518

Which option is a design consideration when using routers in a distributed hardware architecture?

The correct answer is A. Routing information is stored in the RIB and the FIB makes forwarding decisions as programmed. In distributed hardware architectures, the RIB maintained by the control plane programs the FIB into distributed line card ASICs, which then make all forwarding decisions locally at wire rate.

Designing Network Infrastructure

Question

Which option is a design consideration when using routers in a distributed hardware architecture?

Options

  • ARouting information is stored in the RIB and the FIB makes forwarding decisions as programmed
  • BAfter a link failure occurs in the core, the RIB continues to forward the traffic while FIB
  • CBGP routes are stored in the RIB and IGP routes are stored in the FIB
  • DIP routes are stored in the RIB and MPLS labels are stored in the FIB

How the community answered

(30 responses)
  • A
    77% (23)
  • B
    13% (4)
  • C
    7% (2)
  • D
    3% (1)

Why each option

In distributed hardware architectures, the RIB maintained by the control plane programs the FIB into distributed line card ASICs, which then make all forwarding decisions locally at wire rate.

ARouting information is stored in the RIB and the FIB makes forwarding decisions as programmedCorrect

In a distributed hardware architecture, the route processor maintains the RIB as the authoritative control-plane database containing all routing protocol information, and then downloads the best-path entries into the FIB on each distributed line card ASIC. Forwarding decisions are made locally by line cards using the FIB, enabling wire-rate packet switching without involving the central processor per packet.

BAfter a link failure occurs in the core, the RIB continues to forward the traffic while FIB

The RIB is a control-plane database and does not forward traffic - after a link failure the FIB continues forwarding while routing protocols update the RIB with the new topology, then reprogram the FIB.

CBGP routes are stored in the RIB and IGP routes are stored in the FIB

Both BGP and IGP routes are installed into the RIB; the FIB contains best-path forwarding entries derived from the RIB regardless of whether they originated from BGP or an IGP.

DIP routes are stored in the RIB and MPLS labels are stored in the FIB

While MPLS labels reside in a separate LFIB, this statement misrepresents the core distributed-architecture design consideration - the fundamental principle is the separation of the control-plane RIB from the distributed forwarding-plane FIB, not an IP-vs-MPLS split.

Concept tested: RIB vs FIB roles in distributed hardware forwarding architecture

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/xe-16/iri-xe-16-book/iri-arch.html

Topics

#distributed hardware#RIB#FIB#forwarding architecture

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