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59. INTRODUCTION TO NETWORK AUTOMATION

WHY NETWORK AUTOMATION

  • Previous versions of the CCNA focused on the traditional model of managing / controlling networks
  • The current version focuses on the traditional model as well, but CCNA candidates are expected to have a basic understanding of various topics related to network automation
  • In the traditional model, engineers manage devices one at a time by connecting to their CLI via SSH

DOWNSIDES OF CONFIGURING DEVICES ONE-BY-ONE

  • Typos and other small mistakes are common
  • It is time-consuming and very inefficient in large-scale networks
  • It is difficult to ensure that all devices ADHERE to the organization’s STANDARD CONFIGURATION

BENEFITS OF NETWORK AUTOMATION

  • Human Error (Typos, etc) is reduced

  • Networks become much more scalable and implemented in a fraction of the time

    • New deployments
    • Network-wide changes
    • Troubleshooting

  • Network-wide policy compliance can be assured

    • Standard configurations
    • Software versioning

  • The improved efficiency of network operations reduces the OP-EX (operating expenses) of the network. Each task requires fewer man-hours

There are various tools / methods that can be used to automate tasks in the network

- SDN (Software-Defined Networking)
- Ansible
- Puppet
- Python scripts
- etc…

LOGICAL “PLANES” OF NETWORK FUNCTIONS

What does a ROUTER do?

  • It forwards messages between networks by examining information in the Layer 3 header
  • It uses a routing protocol like OSPF to share route information with other routers and build a routing table
  • It uses ARP to build an ARP table, mapping IP Addresses to MAC Addresses
  • It uses Syslog to keep logs of events that occur
  • and MUCH more…

What does a SWITCH do?

  • It forwards messages within a LAN by examining information in the Layer 2 header
  • It uses STP to ensure there are no Layer 2 loops in the network
  • It builds a MAC address table by examining the Source MAC address of frames
  • It uses Syslog to keep logs of events that occur
  • It allows a user to connect to it via SSH and manage it

The various functions of network devices can be logically divided up (categorized) into PLANES

- DATA PLANE
- CONTROL PLANE
- MANAGEMENT PLANE
  • The operations of the MANAGEMENT PLANE and the CONTROL PLANE are usually managed by the CPU
  • However, this is not desirable for DATA PLANE operations because CPU processing is slow (relatively speaking)
  • Instead, a specialized hardware ASIC (Application-Specific Integrated Circuit) is used.
    • ASICs are chips built for a specific purpose
  • Using a SWITCH, as an example:
    • When a FRAME is received, the ASIC (not the CPU) is responsible for the switching logic
    • The MAC Address table is stored in a kind of memory called TCAM (Ternary Content-Addressable Memory)
      • Another common name for the MAC Address table is CAM TABLE
    • The ASIC feeds the DESTINATION MAC address of the FRAME into the TCAM which returns the matching MAC Address table entry
    • The FRAME is then forwarded out of the appropriate DEVICE
  • Modern ROUTERS also use a similar hardware DATA PLANE: An ASIC designed for forwarding logic, and tables store in TCAM

A SIMPLE SUMMARY:

  • When a DEVICE receives CONTROL / MANAGEMENT traffic (destined for itself), it will be processed in the CPU
  • When a DEVICE receives DATA traffic which should pass through the DEVICE, it is processed by the ASIC for maximum speed

DATA PLANE

  • All tasks involved in forwarding USER DATA / TRAFFIC from one INTERFACE to another are part of the DATA PLANE
  • A ROUTER receives a message, looks for the most specific matching ROUTER in its ROUTING TABLE, and forwards it out of the appropriate INTERFACE to the next hop
    • It also de-encapsulates the original LAYER 2 header, and re-encapsulates with a new header destined for the next hop’s MAC address
  • A SWITCH receives a message, looks at the DESTINATION MAC Address, and forwards it out of the appropriate INTERFACE (or FLOODS it)
    • This includes functions like adding / removing 802.1q VLAN tags
  • NAT (changing the SRC / DST addresses before forwarding) is part of the DATA PLANE
  • Deciding to forward / discard messages due to ACL’s, port-security, etc. is part of the DATA PLANE
  • The DATA PLANE is also called the ‘FORWARDING PLANE’

image

CONTROL PLANE

  • How does a DEVICE’s DATA PLANE make its forwarding decisions?

    • ROUTING TABLE
    • MAC ADDRESS table
    • ARP table
    • STP
    • etc…

  • Functions that build THESE tables (and other functions that influence the DATA PLANE) are part of the CONTROL PLANE

  • The CONTROL PLANE controls what the DATA PLANE does, for example by building the ROUTER’s ROUTING TABLE

  • The CONTROL PLANE performs overhead work

    • OSPF itself doesn’t forward user data packets, but it informs the DATA PLANE about HOW packets should be forwarded
    • STP itself isn’t directly involved in the process of forwarding FRAMES, but it informs the DATA PLANE about which INTERFACES should and shouldn’t be used to forward FRAMES
    • ARP messages aren’t user data but they are used to build an ARP TABLE which is used in the process of forwarding data

image

MANAGEMENT PLANE

  • Like the CONTROL PLANE, the MANAGEMENT PLANE performs overhead work
    • However, the MANAGEMENT PLANE doesn’t directly affect the forwarding of messages in the DATA PLANE
  • The MANAGMENT PLANE consists of PROTOCOLS that are used to manage devices
    • SSH / TELNET : Used to connect to the CLI of a DEVICE to configure / manage it
    • SYSLOG : Used to keep logs of events that occur on the device
    • SNMP : Used to monitor the operations of the device
    • NTP : Used to maintain accurate time on the device

image

SOFTWARE-DEFINED NETWORKING (SDN)

  • SOFTWARE-DEFINED NETWORKING (SDN) is an approach to networking that centralizes the CONTROL PLANE into an application called a CONTROLLER
  • SDN is also called SOFTWARE-DEFINED-ARCHITECTURE (SDA) or CONTROLLER-BASED NETWORKING
  • Traditional CONTROL PLANES use a distributed architecture
    • For example:
      • Each ROUTER in the NETWORK runs OSPF and the ROUTERS share routing information and then calculate their preferred routes to each destination
  • An SDN CONTROLLER centralized CONTROL PLANE functions like calculation routes
    • That is just an example and how much of the CONTROL PLANE is centralized varies greatly
  • The CONTROLLER can interact programmatically with the NETWORK DEVICE using APIs (Application Programming Interface)

image

SOUTHBOUND INTERFACE (SBI)

  • The SBI is used for communications between the CONTROLLER and the NETWORK DEVICES it controls

  • It typically consists of a COMMUNICATION PROTOCOL and API (Application Programming Interface)

  • APIs facilitate data exchanges between programs

    • DATA is exchanged between the CONTROLLER and the NETWORK DEVICES
    • An API on the NETWORK DEVICES allows the CONTROLLER to access information on the DEVICES, control their DATA PLANE TABLES, etc.

  • Some examples of SBIs :

    • OpenFlow
    • Cisco OpFlex
    • Cisco OnePK (Open Network Environment Platform Kit)
    • NETCONF

NORTHBOUND INTERFACE (NBI)

  • Using the SBI, the CONTROLLER communicates with the managed DEVICES and gathers information about them:

    • The DEVICES in the NETWORK
    • The TOPOLOGY (how the DEVICES are connected together)
    • The available INTERFACES on each DEVICE
    • Their CONFIGURATIONS

  • The NORTHBOUND INTERFACE (NBI) is what allows us to:

    • Interact with the CONTROLLER
    • Access the DATA it gathers about the NETWORK
    • Program the NETWORK
    • Make changes to the NETWORK via the SBI

  • A REST API (Representational State Transfer) is used on the controller as an interface for APPS to interact with it

  • OSGi (Java Open Services Gateway Initiative) - Java based NBI API

  • DATA is sent in a structured (serialized) format such as JSON or XML

    • This makes it easier for programs to use the DATA

image

AUTOMATION IN TRADITIONAL NETWORKS VS SDN

  • Networking tasks can be automated in traditional NETWORK architectures too:

    • SCRIPTS can be written (ie: using Python) to push commands to many DEVICES at once
    • Python with good use of REGULAR EXPRESSIONS can parse through “show” commands to gather information about network devices

  • However, the robust and centralized DATA collected by SDN CONTROLLERS greatly facilitates these functions

    • The CONTROLLER collects information about all DEVICES in the NETWORK
    • NORTHBOUND APIs allow APPS to access information in a format that is easy for programs to understand (ie: JSON and XML)
    • The centralized DATA facilitates network-wide analytics

  • SDN Tools can provide the benefits of automation without the requirement of third-party scripts and apps.

    • You don’t need expertise in automation to make use of SDN Tools
    • However, APIs allow third-party applications to interact with the CONTROLLER, which can be very powerful

💡 Although SDN and automation aren’t the same thing, the SDN architecture greatly facilitates the automation of various tasks in the network via the SDN CONTROLLER and APIs