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Difficulty: MediumSeparation of Control Plane and Data Plane

A network engineer is analyzing packet processing behavior on a router to differentiate between tasks executed by the general-purpose CPU and tasks handled by specialized forwarding hardware. Which two operational tasks are executed exclusively within the control plane? (Select two.)

  1. Exchanging OSPF hello and link-state messages with neighboring devices to construct the Routing Information Base (RIB)Answer
  2. B
    Performing destination IP address lookups against the Forwarding Information Base (FIB) inside hardware ASICs to switch transit packets
  3. Processing incoming ARP request packets to resolve Layer 3 to Layer 2 address mappings and maintain the ARP cacheAnswer
  4. D
    Filtering transit data frames on interface ingress by matching packet header fields against Access Control List (ACL) entries in TCAM

Answer

The control plane is responsible for exchanging OSPF routing updates to build the RIB and processing ARP requests to manage Layer 2 to Layer 3 address resolution.
The control plane is responsible for generating, receiving, and processing intelligence-building network protocols. Exchanging OSPF messages to calculate routes and populate the Routing Information Base (RIB), as well as processing ARP requests to populate the ARP table, are CPU-bound tasks managed exclusively by the control plane.

Step-by-Step Solution

1
Identify the primary functions of the Control Plane.
The control plane makes intelligent routing decisions, manages neighbor relationships, runs control protocols (OSPF, BGP, ARP), and builds control tables (RIB, ARP table) using the device CPU.
Control plane protocols require complex logic and state management that cannot be hardcoded into hardware ASICs.
2
Identify the primary functions of the Data Plane.
The data plane (forwarding plane) handles high-speed transit traffic forwarding, MAC/FIB lookups in TCAM/ASIC hardware, frame encapsulation/decapsulation, and hardware ACL filtering.
Data plane tasks must occur at wire speed without involving the main CPU for every transit packet.
3
Evaluate each provided operational task against plane responsibilities.
OSPF message exchange and ARP request processing are control plane operations. FIB hardware lookups and TCAM ACL evaluation are data plane operations.
Matching control protocols to CPU processing confirms the two correct control plane tasks.

Key Concept

Separation of Control Plane and Data Plane Responsibilities
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Topics

Separation of Control Plane and Data Plane

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