Which Action Does the Data Plane Perform?

200-301 By islever Editorial Last updated

Determine how a router makes a forwarding decision by default Interpret the components of routing table

Short answer

B The data plane forwards traffic to the next hop using forwarding information already supplied by the control plane.

Question

Which action is taken by the data plane within a network device?
  1. Constructs a routing table based on a routing protocol.
  2. Forwards traffic to the next hop. Correct Answer
  3. Looks up an egress interface in the forwarding information base.
  4. Provides CLI access to the network device.

Key Takeaways

The question tests which plane owns packet forwarding; the trap is selecting the FIB-lookup wording in option C when the FIB itself is assembled by the control plane, and the data plane's defining job is to forward the packet onward.

The data plane (forwarding plane) of a router or switch is the component that actually moves packets onward through the network. This page establishes that forwarding traffic to the next hop is the data plane's defining action, while routing-table construction, FIB building, and CLI access belong to other planes.

Common mistake: Option C is the most tempting wrong pick: learners associate the forwarding information base with hardware forwarding and assume a FIB lookup is the 'best' answer. The FIB is populated by control-plane routing processes (CEF), and B states the data plane's actual responsibility more completely.

Expert Analysis

Why the Answer Is Correct

The data plane — also called the forwarding plane — is defined by Cisco as the part of the device that actually transports packets through the box and onward to the next hop. ricky1802 put it plainly: "The data plane forwards traffic flows." Option B describes exactly that outcome: once forwarding information already exists, the data plane takes the arriving frame, rewrites it, and emits it toward the next-hop device. Options A and D clearly belong to the control plane and the management plane respectively, leaving B as the cleanest description of a data-plane action.

Why the Other Options Are Wrong

Option A describes construction of the routing table, which is produced by routing protocol processes (OSPF, EIGRP, static routes) running in the control plane. Option C is a partially defensible distractor — the data plane hardware does consult the FIB during forwarding — but the FIB itself is built by control-plane CEF processes, and B captures the plane's overall responsibility rather than one sub-step, which is why most learners and commenters treat B as the intended answer. Option D, CLI access, is a management-plane function (console, SSH, Telnet). No_blink404 even conceded it is a "Poorly written question, but B would be the answer."

Community Comment Notes

The community strongly favored B, with ricky1802, Bankultimate, FALARASTA, Wintza, and MeysamDavabi all selecting it. Yinxs observed "B and C are all correct," and Joshua25 argued the reverse, noting the FIB "is built by the control plane, but utilised by the data plane," even calling the item faulty. MeysamDavabi split the difference, saying the FIB lookup and forwarding are related but that "B is the more comprehensive answer." No comment supplied any official citation, so the verdict here rests on Cisco's plane definitions rather than on the vote tally.

Exam Strategy

When a question contrasts planes, first eliminate options describing table building (control plane) and administrative access (management plane), then choose the option that states the plane's overall responsibility rather than a sub-mechanism. On ambiguous CCNA items, the broadest correct definition of the plane's role is usually the keyed answer.

Frequently Asked Questions

Why is building the routing table not a data plane action?

Routing protocols and FIB construction run in the control plane; the data plane only consumes that prebuilt information to move packets onward.

Does the data plane also perform the FIB lookup in option C?

Yes, hardware forwarding does consult the FIB, but option C names a sub-step while B states the data plane's overall responsibility, which is the intended answer.

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Discussion 12 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 12

  1. ricky1802 👍 8 Answered B
    The data plane forwards traffic flows. The data plane is the forwarding plane, which is responsible for the switching of packets through the router.
  2. Yinxs 👍 4 Answered B
    B and C are all correct.
  3. Bankultimate 👍 3
    B is correct.
  4. no_blink404 👍 2 Answered B
    Poorly written question, but B would be the answer
  5. Iamm 👍 2 Answered C
    believe better answer
Show 7 more comments
  1. FALARASTA 👍 2
    B is correct
  2. baanyan 👍 1
    I choose D, for C, since CEF consists of FIB and Adjacency Tables. FIB is structured as a tree of 4 layers, and each layer has node from 0-255(destination address quick look up). At each leaf node, it has a pointer to the Adjacency table. CEF uses the Adjacency table to prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries. So, it looks for the adj table for egress interface not FIB
  3. Iamm 👍 1
    i believe correct answer is C. Looks up an egress interface in the forwarding information base. Question mentioned "data plane", not control plane, so control plane determine first: Next hop then output interface, so "data plane must only get to the egress interface (and there is no need for going to another network it will happens if the network device relates to the same segment). Makes more sense for me.
  4. PaddyInNZ 👍 1
    Option 'b' is correct. By definition, (official cert guide) "The term data plane refers to the tasks that a networking device does to forward a message". Further, not all devices may have a FIB, so that can rule out option 'c'.
  5. MeysamDavabi 👍 1
    forwarding information base (FIB) is including look up egress interface for find the best path that is why both C and B are related to data plan but B is the more comprehensive answer. B is correct
  6. Joshua25 👍 1 Answered C
    B and C are both within data plane. FIB is built by the control plane, but utilised by the data plane. It is the data plane that looks up the destination in the FIB. This question is faulty.
  7. Wintza 👍 1 Answered B
    Correct

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