Chapter 45 - Introduction to Controller-Based Networking

Question 1

What is the Data Plane of a network?

Answer 1

• The tasks that a network device completes to forward a message. Regardless of whether it is Layer 2, or 3.
• Handled by an ASIC more often than the CPU
• Also known as the Forwarding Plane
• Examples of tasks completed at the Data Plane are:
  - Encapsulating and deencapsulating a packet in a frame
  - Adding or removing an 802.1Q header
  - Matching a MAC to its entry in a MAC Address Table
  - Matching an IP to its entry in a Routing Table
  - Encrypting data and adding a new IP header for VPN
  - Changing source or destination address for NAT
  - Discaring a message due to a filter for ACLs or port security

Question 2

What is the Control Plane of a network?

Answer 2

• Provides data to the Data Plane so that it can perform its tasks. Performs overhead work.
• Handled by the CPU
• Controls the Data Plane
• Examples of data sourced by the Control Plane is:
  - Routing Protocols
  - IPv4 ARP
  - IPv6 NDP
  - Switch MAC Learning
  - STP

Question 3

What is the Management Plane of a network?

Answer 3

• Contains protocols that allow engineers to manage hardware. Performs overhead work.
• Handled by the CPU
• Examples of Management Plane protocols are:
  - Telnet
  - SSH
  - SNMP
  - Syslog

Question 4

What is SDN?

Answer 4

• Software Defined Networking
• Also known as Software Defined Architecture or Controller Based Networking
• Uses a Centralised Control Plane via an SDN Controller. Although some SDNs centralise the control plane more than others.
• Interacts with networking devices via APIs

Question 5

What is a Distributed Control Plane?

Answer 5

• This is when the control plane of a network is distributed between multiple devices rather than being centralised to a Controller
• For example, multiple routers connected running OSPF will communicate routes with each other
• Used in traditional networks

Question 6

What is a Centralised Control Plane?

Answer 6

• A control plane that has all of its control plane data stored and processed by a single device. A controller.

Question 7

What are examples of SBIs?

Answer 7

• OpenFlow
• OpFlex - Uses a declarative SDN model
• Telnet/SSH and SNMP used with Cisco APIC-EM (Controller)
• Telnet/SSH, SNMP, and NETCONF used with Cisco Software Defined Access (Controller)
• OnePK - Cisco proprietary

Question 8

What is a Southbound Interface?

Answer 8

• SBI for short
• The virtual interface on a Controller that connects to the networking devices it controls
• Often utilises an API to allow the Controller to communicate with networking devices and program the Control Planes of each networking device with data that is used by the Data Plane

Question 9

What is an API?

Answer 9

• Application Programming Interface
• A way of allowing one application to exchange data with another

Question 10

What information would a Controller gather about its network?

Answer 10

• A list of all devices in the network
• The capabilities of each device
• The interfaces on each device
• The current state of each interface
• The topology (which devices connect to which via which interfaces)
• Device configuration (IP Addresses, VLANs)

Question 11

What is a Northbound Interface?

Answer 11

• NBI for short
• The virtual interface on a Controller that allows its data and functions to be used by other programs. Also what allows engineers access to the controller.
• Often uses an API to allow the Controller to communicate with applications. The applications are sometimes located on the same machine, sometimes elsewhere in the network. In this situation a REST API is required.

Question 12

What is a REST API?

Answer 12

• Representational State Transfer Application Programming Interface
• Utilised in instances where the Controller is not located on the same system as an application that wants to access it.
• Allows HTTP messages to be sent between Controller and application over the network
• Not an API itsself but defines how an API should work

Question 13

What are the common formats used for network programming?

Answer 13

• JSON (JavaScript Object Notation)
• XML (eXtensible Markup Language)

Question 14

List SDN solutions

Answer 14

• OpenDaylight Controller
• Cisco Application Centric Infrastructure (ACI)
• Cisco APIC Enterprise Module (APIC-EM)

Question 15

What is the ONF?

Answer 15

• Open Networking Foundation
• A community of users and vendors that aim to establish SDN in the market
• Developed the OpenFlow model SDN which defines the protocols and standards that SDNs use. For example it defines the concept of a controller and the standards a switch needs to follow in order to support OpenFlow (Switch Abstraction)

Question 16

What is ACI?

Answer 16

• Application Centric Infrastructre
• SDN Developed by Cisco for use in data centres
• Uses an IBN (Intent Based Networking) model which defines which endpoints (e.g. VMs, Containers, Servers) can communicate and which can’t. Endpoints (leaves) are put into EPGs (End Point Groups) within the APIC (Application Policy Infrastructure Controller) and have policies applied to them to define this. The APIC takes care of the actual configuration dynamically.
• Partially centralises the control plane and centralises the management plane

Question 17

What is APIC-EM?

Answer 17

• Application Policy Infrastructure Controller Enterprise Module
• Developed by Cisco as an SDN solution that allowed organisations to utilise SDN while still using their current networking devices
• Does not centralize the control plane but does centralize the management plane
• Provides management features such as:
  - Topology map - Discovers and displays the topology of the network
  - Path trace - User supplies a source and destination and the application shows the path through the
  network as well as forwarding decisions to get there
  - Plug and Play - Provides day 0 installation support so a new device can be reachable through automation
  via the controller straight out of the box
  - Easy QoS
• Uses Telnet, SSH, or SNMP as SBI
• Succeeded by DNA Centre

Question 18

What is OpenFlow?

Answer 18

• Open source SDN solution
• Uses OpenDaylight as controller
• Centralises the control plane to a large degree and also the management plane
• Uses OpenFlow as SBI
• Uses imperative SDN model

Question 19

How does automation impact network management and configuration?

Answer 19

• NBIs and controllers make it much easier to automate functions versus traditional networks
• More consistent configuraiton and less errors
• Allows for more advanced analytics that provide better insights versus traditional networks
• Time required to complete projects is reduced
• EPGs mean that devices don’t have to be configured individually via commands

Question 20

Examples of automation in traditional networks

Answer 20

• Scripts (e.g. Python) can be used to parse lots of show commands for data and send configuration commands to multiple devices at once

Question 21

What are the different layers of an SDN architecture?

Answer 21

• Application layer - Contains applications that tell the SDN what is required
• Control layer - Contains the SDN controller
• Infrastructure layer - Contains the data plane

Question 22

Examples of NBIs

Answer 22

• OSGi
  -REST