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Difficulty: MediumSeparation of Control Plane and Data Plane

Network architectures strictly differentiate operational responsibilities between planes to ensure scalability and high-speed processing. Which two of the following tasks are performed by the control plane rather than the data plane? (Select two.)

  1. Building and maintaining the Routing Information Base (RIB) through dynamic routing protocols.Answer
  2. Processing incoming ARP requests that are directly addressed to the local router interface.Answer
  3. C
    Performing longest prefix match lookups on transit packets using hardware ASICs.
  4. D
    Decrementing the IP Time-to-Live (TTL) field and rewriting Layer 2 headers on forwarded packets.

Answer

Building and maintaining the Routing Information Base (RIB) through dynamic routing protocols, and processing incoming ARP requests that are directly addressed to the local router interface.
The correct options identify operations belonging to the control plane. Dynamic routing protocols run on the control processor to construct the Routing Information Base (RIB). Additionally, packets addressed directly to the routing device itself—such as ARP queries directed to the local router interface—cannot be handled solely by forwarding ASICs and must be punted to the control plane for processing. Conversely, packet switching, hardware FIB lookups, TTL updates, and MAC address rewrites for transit packets occur exclusively within the data plane.

Step-by-Step Solution

1
Analyze the operational responsibilities of the control plane.
The control plane manages protocol operations, path calculations, building the RIB, and handling traffic destined to the router itself (such as ARP requests for local interface IPs or routing updates).
Control plane tasks require complex processing logic handled by the main CPU.
2
Analyze the operational responsibilities of the data plane.
The data plane (forwarding plane) processes transit traffic passing through the router. It uses specialized hardware (ASICs and TCAM) to perform FIB lookups, TTL decrements, and Layer 2 frame header rewrites at wire speed.
Data plane functions are optimized for fast throughput and low latency without consuming main processor CPU cycles.
3
Evaluate the choices to select the two control plane operations.
RIB maintenance via routing protocols and processing ARP requests for local interface addresses are control plane functions. Hardware FIB lookups and packet header modifications are data plane functions.
Correctly separates plane duties based on whether the task involves network-wide intelligence/self-destined traffic versus transit packet switching.

Key Concept

Control Plane vs. Data Plane Responsibilities
Estimated Time:1m 30s
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Topics

Separation of Control Plane and Data Plane

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