What Network Node Function is Centralized on an SDN Controller?

200-301 By islever Editorial Last updated

Describe controller-based, software defined architecture (overlay, underlay, and fabric)

Short answer

A Creating the IP routing table is centralized on the controller as a control plane function.

Question

In an SDN architecture, which function of a network node is centralized on a controller?
  1. Creates the IP routing table Correct Answer
  2. Discards a message due filtering
  3. Makes a routing decision
  4. Provides protocol access for remote access devices

Key Takeaways

SDN centralizes control plane functions like building the routing table on the controller, while data plane functions like making forwarding decisions remain on the local network nodes.

In a Software-Defined Networking (SDN) architecture, the control plane is decoupled from the data plane and centralized on the controller. This page establishes that creating the IP routing table is the specific function centralized on the controller.

Common mistake: Choosing 'Makes a routing decision' (C) because it sounds like a control plane task, but making a forwarding decision is actually a data plane function performed locally by the switch.

Expert Analysis

Why the Answer Is Correct

In an SDN architecture, the control plane is logically centralized on the SDN controller, separating it from the individual network nodes. The primary function of the control plane is to run routing protocols, learn network topology, and build the IP routing table. Because this intelligence is centralized, creating the IP routing table is the function performed by the controller.

Why the Other Options Are Wrong

Options B and C are data plane (forwarding plane) functions. Making a routing decision (forwarding a packet based on the table lookup) and discarding a message due to filtering are actions performed locally by the network node's hardware. Option D is a management or data plane function for remote access, not a control plane function centralized in SDN.

Community Comment Notes

The community correctly identified that creating the routing table is a control plane process, as noted by a user who stated "creating routing table is a control plane process, hence A". Another user clarified the distinction by pointing out that "data plane makes routing decisions based on control plane routing table," which perfectly explains why option C is a local node function rather than a centralized one.

Official Reference

https://www.cisco.com/c/en/us/solutions/software-defined-networking.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

Memorize the three SDN planes: Management, Control, and Data. The SDN controller centralizes the Control Plane (building routing tables and topology), while the Data Plane (forwarding decisions, filtering) stays on the physical devices.

Community Votes

A
78%
C
22%

78% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 33 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 30 of 33

  1. clivebarker86 👍 28
    control plane, create routing table
  2. DeeB0 👍 8
    My disdain for Cisco grows...
  3. TinKode 👍 7
    And data plane makes routing decisions based on control plane routing table.
  4. Starlord2535 👍 4
    789 What is the function of the controller in a software-defined network? A. forwarding packets B. multicast replication at the hardware level C. setting packet-handling policies D. fragmenting and reassembling packets
  5. askar430 👍 4 Answered A
    Routing Decision = Routing Matching table , so its not correct , i think A the better one
Show 25 more comments
  1. Sant11 👍 3 Answered C
    In the context of an SDN architecture, the function that is primarily centralized on a controller is indeed: C. Makes a routing decision While it's true that SDN controllers can have an impact on the overall IP routing table, the centralization of routing decisions is a more accurate and fundamental representation of the controller's role in an SDN environment. Option A ("Creates the IP routing table") involves the process of populating the routing table with routes and their associated information. While an SDN controller can influence routing decisions by programming forwarding rules in network devices, the creation of the IP routing table typically involves the management of routing protocols, which might still be distributed across the network devices. So, while both options A and C have connections to the controller's role in SDN, option C is a more direct and specific representation of how SDN controllers primarily centralize routing decisions.
  2. fd17639 👍 3 Answered C
    C. Makes a routing decision In an SDN (Software-Defined Networking) architecture, the function of making routing decisions is centralized on a controller. In SDN, the control plane, which involves tasks such as making routing decisions and managing network traffic, is separated from the data plane. The SDN controller is responsible for making decisions about how data should be forwarded through the network. This centralized control allows for more dynamic and programmable network management.
  3. Starlord2535 👍 3 Answered C
    A SDN consists of control, data, and management planes. The control plane performs forwarding decisions and other functions, like quality of service (QoS). In contrast, the data plane is the network that switches or forwards devices handling the data packets and taking inputs from the control plane. https://www.splunk.com/en_us/blog/learn/control-plane-vs-data-plane.html#:~:text=It%20is%20responsible%20for%20routing,path%20for%20forwarding%20network%20traffic.
  4. enzo86 👍 3
    the answer is A The term control plane refers to any action that controls the data plane. Most of these actions have to do with creating the tables used by the data plane, tables such as the IP routing table, an IP Address Resolution Protocol (ARP) table, a switch MAC address table, and so on.
  5. Starlord2535 👍 3
    760 What is the function of the controller in a software-defined network? A. forwarding packets B. multicast replication at the hardware level C. making routing decisions D. fragmenting and reassembling packets Answer C best choice
  6. kalitwol 👍 3 Answered A
    Making a routing decision = looking up destination route, which is an action done for a message....this a data plane process However creating routing table is a control plane process, hence A
  7. michael1001 👍 3 Answered C
    C is correct - Several articles on the purpose of an SDN controller confirms that the controller becomes the control plane exists in the middle of the management and data plane.
  8. exiledwl 👍 3 Answered C
    Im going with C as well
  9. bymrdas 👍 3 Answered C
    C is Correct
  10. matass_md 👍 3 Answered C
    C FTW!
  11. wakaish 👍 2
    Makes a routing decision In a Software-Defined Networking (SDN) architecture, the function of making routing decisions is centralized on a controller. SDN decouples the control plane from the data plane, meaning that the intelligence for making routing decisions is moved from individual network devices (such as switches and routers) to a centralized controller. The controller manages the network and makes routing decisions based on the overall network state, traffic patterns, and policies, which allows for more dynamic and programmable network configurations. This centralization of control is a key feature of SDN and enables more efficient network management and automation. Re
  12. Liquid_May 👍 2 Answered A
    In the 31 Days Before CCNA Guide on page 813 the following is stated: "The data plane is responsible for forwarding data as quickly as possible. To do so, it relies on tables built by the control plane". In the same page it is stated that one of the functions of the data plane is performing IP routing table lookups. Based on that, I would say that making a routing decision, would be a data plane function and to create the IP routing table would be a control plane function.
  13. NewJeans 👍 2 Answered A
    The answer is absolutely A. According to the 31 days before CCNA, 1) In SDN, the functions of the control plane can be completely removed from the physical networking devices and placed in a centralized application called a controller. 2) A traditional networking device contains two planes. The data plane is responsible for forwarding data as quickly as possible. To do so, it relies on tables built by the control plane. What is the tables built by the control plane?
  14. 760ac40 👍 2 Answered A
    What's the difference between "creates the IP routing table" and "makes a routing decision"? If you make a routing decision, it's because you previously reviewed the information in the IP routing table. So, I think A and C are correct, but in this case, A is only slightly more correct than C. Also, if C were correct, then A is incorrect? Who creates the IP routing table?
  15. Starlord2535 👍 2
    792 Which network plane is centralized and manages routing decisions? A. management plane B. data plane C. policy plane D. control plane Control plane is centralized while data plane is distributed
  16. danny43213 👍 2
    one of the functions of a data plane is matching the destination IP address IP address to the routing table i.e routing decission but the table is in the control plane therfore I go with A.
  17. RougePotatoe 👍 2
    Question 760 is a similar question and its answer was make routing decisions
  18. matteodd90 👍 2 Answered A
    The function of a network node centralized on a controller is control plane
  19. a67c04a 👍 2 Answered A
    It´s A - control plane
  20. ds0321 👍 2 Answered A
    the answer is A
  21. 0920136 👍 1 Answered A
    In an SDN architecture, the function that is centralized on the controller is: A. Creates the IP routing table This is correct because: In SDN, the control plane is separated from the data plane and centralized in the SDN controller. The control plane is responsible for making decisions about where traffic should be sent, which includes creating and maintaining routing tables. The SDN controller acts as the "brain" of the network, maintaining a global view of the network topology and making centralized decisions about routing and forwarding. One of the key functions of the SDN controller is to calculate and distribute routing information to the network devices (switches and routers) in the data plane. This includes creating and updating IP routing tables. By centralizing this function, SDN allows for more efficient and dynamic routing decisions based on real-time network conditions and policies.
  22. NetworkDisciple 👍 1
    Official Cert Guide Vol 2 Page 360 "The term control plane refers to any action that controls the data plane. Most of these actions have to do with creating the tables used by the data plane, tables like the IP routing table, an IP Address Resolution Protocol (ARP) table, a switch MAC address table, and so on. By adding to, removing, and changing entries to the tables used by the data plane, the control plane processes control what the data plane does. You already know about many control plane protocols—for instance, all the IP routing protocols."
  23. zbeugene7 👍 1
    From Odom book: "The term control plane refers to any action that controls the data plane. Most of these actions have to do with creating the tables used by the data plane, tables like the IP routing table, an IP Address Resolution Protocol (ARP) table, a switch MAC address table, and so on. By adding to, removing, and changing entries to the tables used by the data plane, the control plane processes control what the data plane does"
  24. zbeugene7 👍 1
    I think I unraveled the conundrum: the key is the difference between "forwarding" and "routing", by definition data plane is forwarding not routing, routing decision is not "forwarding". What data plane does is a lookup of the destination routes to find a match before the packet is forwarded. This is not a routing decision, therefore correct answer is C, because this is a function of the control plane.
  25. Tompoo 👍 1 Answered C
    In Software-Defined Networking (SDN), the control plane is centralized on an SDN controller. The control plane is responsible for making decisions about where traffic should be forwarded.

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