O'Reilly logo
live online training icon Live Online training

How Routers Really Work: Network Operating Systems and Packet Switching

Russ White

A network device—such as a router, switch, or firewall—is often seen as a single “thing,” an abstract appliance that is purchased, deployed, managed, and removed from service as a single unit. While network devices do connect to other devices, receiving and forwarding packets and participating in a unified control plane, they are not seen as a “system” in themselves.

This training will peer into the internal components of a router, starting with an explanation of how a router switches packets. This walk through of a switching path, in turn, will be used as a foundation for explaining the components of a router, including the various tables used to build forwarding tables and the software components used to build these tables.

With this information in the background, the webinar will examine the architecture of several network operating systems in order to “flesh out” the concepts considered.

This training is important because it allows engineers to “get inside” a router so they can understand precisely what a router does, and how it does it. This will help engineers more quickly understand why packet flows are being treated in specific ways, how to understand quality of service, and how to think about the components needed to build a disaggregated solution.

What you'll learn-and how you can apply it

By the end of this course, participants will understand how a router, or other network device, does the work of switching packets from an input interface to an output interface.

This training course is for you because...

This course is for you if you want to understand:

  • the process of switching a packet through a network device
  • how all the protocols a network device runs work together to build the information required to switch a packet
  • how and where quality of service is implemented in a switching path
  • the various software and hardware components necessary to build a disaggregated solution at the network device level


  • Basic understanding of control planes
  • A basic idea of the various protocols used in an IPv4/IPv6 network

About your instructor

  • Russ White began working with computers in the mid-1980's and computer networks in 1990. He has co-authored forty-seven software patents, participated in the development of several Internet standards, helped develop the CCDE and the CCAr, and worked in Internet governance with the Internet Society. Russ is a co-host of the History of Networking and Hedge podcasts, serves on the Routing Area Directorate at the IETF, co-chairs the BABEL working group, and serves on the Technical Services Council/as a maintainer on the open source FR Routing project. Russ holds an MSIT from Capella University, an MACM from Shepherds Theological Seminary, and is a PhD Candidate in philosophy at SEBTS.


The timeframes are only estimates and may vary according to how the class is progressing

Segment 1: Switching a Packet

Length: 50 minutes

  • Receiving a packet off the physical wire
  • Initial phases of packet switch
  • Packet switch
  • Carrying the packet from the input interface to the output interface
  • Queueing the packet on the outbound interface
  • Sending a packet onto the physical wire

Break: 10 mins

Segment 2: Building the Tables Required to Switch a Packet

Length: 50 minutes

  • Information in the forwarding table
  • Information provided by the routing table
  • How the routing table gets this information
  • Information provided by interlayer discovery tables
  • How the interlayer discovery tables are built
  • How the MAC header rewrite string is built

Segment 3: Examples

Length: 50 minutes

  • SONiC architecture and walk-through
  • FR Routing architecture
  • Common forwarding chipsets and forwarding APIs

Q&A: 10 minutes