How Networks Really Work

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This webinar will help you understand how networking technologies really work and why they were designed that way.

Last modified on 2024-03-13 (release notes)


How Networks Really Work

1:21:13 Free items Fallacies of Distributed Computing

The typical network characteristics have been misunderstood for decades, resulting in well-known Fallacies of Distributed Computing. In this introductory section, we'll revisit those fallacies and explore how they apply to modern networks.

Fallacies of Distributed Computing 9:18 2020-01-10
Network Is (Not) Reliable 12:58 2020-01-10
Latency Is (Not) Zero 13:42 2020-01-10
Bandwidth Is (Not) Infinite and Free 9:05 2020-01-10
Networks Are (Not) Secure 15:14 2020-01-10
Internet Has More than One Administrator 8:07 2020-01-10
Networks Are (Not) Homogenous 7:37 2020-01-10
What Can You Do 5:12 2020-01-10

Test Your Understanding

Review Questions 1.6K 2020-04-11

Additional Information

Fallacies of Distributed Computing (Wikipedia)
Fallacies of Distributed Computing Explained (Software Developer View)
Understanding the 8 fallacies of Distributed Systems
You don’t know jack about Network Performance (ACM Queue)
The Law of Leaky Abstractions
The Psychology of Web Performance
IPv6 Security Researcher Getting Bored at Brussels Airport
Some Internet Service Providers Should Really Know Better
BGP- and Car Safety
Schneier's Law (of Security Systems)
Memcrashed (CloudFlare blog)

3:50:54 Free items Network Security Fallacies

Most network security vulnerabilities exploit the unfounded trust in the network infrastructure, from neighbors on local area networks and source IP addresses, to transport infrastructure and adjacent routers.

Root Causes 13:39 2023-03-27
Ghost in the Wires by Kevin Mitnick

49:56 Trusting LAN neighbors

Address and Session Hijacking 15:30 2023-03-27
Router Impersonation Attacks 16:40 2023-03-27
VLAN and Encapsulation Attacks 17:46 2023-03-27

35:51 Trusting Source IP Addresses

IP Source Routing Attacks 9:23 2023-03-27
Spoofing Source IP Addresses 10:41 2023-03-27
Unidirectional and Amplification Attacks 15:47 2023-03-27

51:36 Data- and Control-Plane Attacks

Insecure Tunnels and Other Data Plane Attacks 20:22 2023-04-20
Control-Plane Denial-of-Service Attacks 20:08 2023-04-20
Routing Attacks 11:06 2023-04-20

33:21 Internet Routing Security

History of BGP Route Leaks 14:30 2023-04-20
Hacking BGP for Fun and Profit 9:40 2023-04-20
Disruptions Caused by BGP Bugs 9:11 2023-04-20

8:52 Conclusions

The Way Forward 8:52 2023-04-20

37:39 Zero-Trust Architecture (from Design Clinic)

ZTNA Overview 9:28 2023-03-15
Microsegmentation in Zero-Trust World 15:02 2023-03-15
Zero-Trust Solutions 13:09 2023-03-15

More Information (Trusting LAN Neighbors)

IPv6 Security: Getting Bored @ BRU Airport
You MUST Take Control of IPv6 in Your Network
IPv6 Router Advertisement Guard (RA-Guard) Evasion
Security Implications of IPv6 Fragmentation with IPv6 ND (RFC 6980)
Ping of Death in IPv4 and IPv6 (Wikipedia)
VLAN Hopping (Wikipedia)
History of Ethernet Encapsulations
Hiding Malicious Packets Behind LLC SNAP Header

More Information (Trusting Source IP Addresses)

How Do Lava Lamps Help with Internet Encryption
Deprecation of Type 0 Routing Headers in IPv6 (RFC 5095)
Resetting TCP Connections via Spoofed ICMP Error Messages
MASSCAN: Mass IP Port Scanner

32:20 Free items An Overview of Networking Challenges

After briefly exploring the common networking misunderstandings, let's see what makes networks as complex as they are. We'll start with the typical networking challenges, introduce various transmission technologies, and explore the functionality we need to grow our network beyond two nodes.

Introducing Networking Challenges 12:38 2019-08-02
Introducing Transmission Technologies 8:13 2019-08-02
Beyond Two Nodes 11:29 2019-08-02

Test Your Understanding

Review Questions 3.2K 2020-04-17

45:22 Free items The Importance of Networking Layers

Once we've identified more than a dozen challenges we have to solve to build reliable networks, we have to find a framework that allows us to build a robust system. As usual, layering and abstractions help, and we'll explore how we can use semi-independent layers to build modern network stacks.

The Need for Network Layers 7:42 2019-08-02
Retransmissions and Flow Control 13:57 2019-08-02
Missing Layers 6:09 2019-08-02
Putting It All Together 8:39 2019-11-03
Breaking the End-to-End Principle 8:55 2019-08-02

Test Your Understanding

Review Questions 3.7K 2020-04-17

Additional Information

Some Internet Architectural Guidelines and Philosophy (RFC 3439)
Architectural Principles of the Internet (RFC 1958)
The world in which IPv6 was a good design
IPv4, IPv6, and a sudden change in attitude

2:07:20 Free items Network Addressing

There are two hard problems in computer science: cache invalidation and naming things. Network addressing needs to solve both problems.

This section starts with an overview of historical approaches to the network addressing, describes modern data-link- and network-layer addressing, and explores the complexities of address assignments, address scopes, and address translations.

Network Addressing Introduction 10:33 2020-02-01
Theoretical View of Network Addressing 9:48 2020-02-01
Early Data Link Layer Addressing Mechanisms 7:58 2020-02-01
Local Area Network Addressing 8:56 2020-02-01

42:20 Network Layer Addressing

Network Layer Addressing 11:03 2020-02-01
Comparing IP and CLNP Addressing 22:41 2020-02-01
Combining Data-Link and Network Addresses 8:36 2020-02-01
Address Assignments 20:08 2020-02-01
Address Scope 11:34 2020-02-01
Network Address Translation 16:03 2020-02-01

Test Your Understanding

Review Questions 6.0K 2020-04-30

More Information

Inter-Network Naming, Addressing, and Routing
Multihomed IP hosts

3:35:29 Free items Switching, Routing and Bridging

Decades ago we were talking about bridging (forwarding on data-link layer) and routing (forwarding on network layer)... and then vendor marketers invented switches.

This section starts with forwarding terminology, continues with an overview of mechanisms one can use to get packets across the network (ranging from Token Ring Source Route Bridging to Segment Routing in IPv6), and concludes the journey with an outline of techniques used to discover paths across the network, from controller-based topology computation to transparent bridging and routing protocols.

Terminology 21:12 2020-09-18
Getting Packets Across the Network 18:57 2020-09-18
Multi-Layer Switching and Tunneling 13:21 2020-09-18
Finding Paths Across the Network 14:06 2020-09-18
Path Discovery in Routing and Transparent Bridging 21:23 2020-09-18
Store-and-Forward and Cut-Through Switching 15:30 2020-12-01

1:38:43 Comparing Transparent Bridging and IP Routing

Recap: Transparent Bridging Fundamentals 20:47 2020-11-20
Recap: IP Routing Fundamentals 9:50 2020-11-20
Comparing Transparent Bridging and IP Routing 17:55 2020-11-20
Typical Large-Scale Bridging Use Cases 17:55 2020-11-20
Bridging Beyond Spanning Tree Protocol 19:05 2020-11-20
Routing on Host Routes 13:11 2020-11-20

Test Your Understanding

Review Questions 19K 2020-08-07

12:17 From the Design Clinic

Point-to-Point versus VLAN Interfaces 12:17 2021-12-27

More Information: Switching, Routing and Bridging

Lies, Damned Lies, and Product Marketing
How did we ever get into this switching mess?
Is Layer-3 Switch More than a Router?
Why is TRILL not routing at layer-2
Bridging and Routing: is there a difference?
Bridging and Routing, Part II
Spanning Tree Protocol (STP) and Bridging Loops
Musings on IP Packet Reordering
Local Area Mobility (LAM) – the true story
Modern router architecture and IPv6

A fantastic introductory-level description of what routers do and how you could implement packet forwarding in hardware.

More Information: Stretched VLANs

Revisited: The Need for Stretched VLANs
When All You Have Are Stretched VLANs...
Stretched Layer-2 Subnets in Azure
The Difference between Metro Ethernet and Stretched Data Center Subnets
Are VXLAN-Based Large Layer-2 Domains Safer?

More Information: Stretched Clusters

Stretched Clusters: almost as Good as Heptagonal Wheels
Long-Distance vMotion, Stretched HA Clusters and Business Needs
Sometimes You Have to Decide How Badly You Want to Fail
Stretched Firewalls: a Ticking Bomb
Stretched VLANs and Failing Firewall Clusters
Reliability of Clustered Solutions: Another Data Point
Using BGP for Firewall High Availability

More Information: MPLS

LDP-IGP Synchronization in MPLS Networks

2:27:02 Free items Routing Protocols

Routing protocols are the magic that makes networks work. It doesn't matter if you're using a traditional (autonomous) network devices or an SDN controller, someone has to discover the network topology and the attached endpoints, and calculate the optimum paths across the network.

This section introduces the challenges routing protocols have to solve and describes the high-level concepts of link-state and distance-vector routing protocols. Armed with this knowledge you'll find it easier to understand the implementation details of individual protocols like OSPF, IS-IS, EIGRP or BGP.

Routing Protocols Overview 13:01 2020-12-19
Link State Routing Protocol Basics 12:50 2020-12-19
Link State Routing Protocol Implementation Considerations 19:28 2020-12-19
Scaling Link State Routing Protocols 8:05 2020-12-19
Distance Vector Routing Protocol Basics 11:34 2020-12-19
Advanced Distance Vector Routing Protocols 11:48 2020-12-19
Selecting the Optimal Routing Protocol 14:31 2020-12-19
Typical Use Cases 7:36 2020-12-19

Test Your Understanding

Review Questions 15K 2020-09-20
Data Center Routing with RIFT
OpenFabric with Russ White
Is BGP Good Enough with Dinesh Dutt

48:09 From the Design Clinic

Routing Protocol Selection 22:30 2022-03-01
Adapting Routing Protocol Design to Transport Technologies 10:56 2022-03-01
Routing Protocols in Multi-Layer Transport Environments 14:43 2022-03-01

More Information

RIBs and FIBs (aka IP routing table and CEF table)
BGP in Data Center Fabrics
What Happens If You Redistributed BGP Full Table into OSPF?
Equal Routes (and Load Balancing)
IS-IS Is Not Running over CLNP

3:08:39 Free items Advanced Routing Protocol Topics

Routing protocols became increasingly complex over the last four decades as they had to deal with environments they were never designed to support like very fast convergence, or massive amount of routing information. This section describes some of the advanced routing protocol technologies and solutions including:

  • Fast failure detection and convergence
  • Shared fate and trusting routing information
  • Equal- and Unequal Cost Multipath forwarding

48:53 Convergence

Routing Protocol Convergence 12:27 2021-06-19
Convergence in Link State Routing Protocols 7:22 2021-06-19
Convergence in Distance Vector Routing Protocols 12:00 2021-06-19
Detecting Link and Node Failures 17:04 2021-06-19
Micro-BFD: BFD over LAG (Port Channel)
What Exactly Happens after a Link Failure?

26:53 Shared Fate and Trusting Next Hops

Fate Sharing and Trusting Next Hops 14:18 2021-06-19
Trusting BGP Next Hops 12:35 2021-06-19
Can We Trust BGP Next Hops (Part 1)?
Can We Trust BGP Next Hops (Part 2)?
Response: Next-Hop and VTEP Reachability in EVPN Networks
Podcast: Trusting Routing Protocols
Must Read: Redistributing Full BGP Feed into OSPF

1:40:11 Multipath Forwarding

Multipath Forwarding Overview 9:55 2021-06-19
Multipath Topologies 23:00 2021-10-29
BGP Multipath Basics 17:29 2021-10-29
BGP Multipath in Data Center Fabrics 8:32 2021-10-29
Multipath Packet Forwarding Basics 15:54 2021-10-29
Multipath Packet Forwarding Challenges 25:21 2021-10-29
Does Unequal-Cost Multipathing Make Sense?
Single-Metric Unequal-Cost Multipathing Is Hard
Unequal-Cost Multipath in Link State Protocols
Unequal-Cost Multipath with BGP DMZ Link Bandwidth
Local TCP Anycast Is Really Hard
Equal Routes (
DLSP – QoS-Aware Routing Protocol (Software Gone Wild Podcast)
Understanding Load Balancing on Network Devices (Christopher Hart)
Flow Distribution Across ECMP Paths (Dip Singh)

12:42 From the Design Clinic

Monitoring ECMP Behavior in Leaf-and-Spine Fabric 12:42 2022-04-02

1:49:52 Fast Failover

If you want to design a network that converges in tens of milliseconds you can no longer rely solely on routing protocols; the only solution is local repair. This section describes several local repair (fast reroute) technologies that can be used for temporary path repair until the routing protocol convergence process calculates the new best path:

  • Prefix Independent Convergence (PIC)
  • MPLS Fast Reroute (FRR)
  • Loop-Free Alternate (LFA) including Remote LFA and Topology Independent LFA
Fast Failover Basics 11:13 2022-03-26
Planning and Designing Fast Failover 13:09 2022-03-26

31:34 Prefix-Independent Convergence

Prefix-Independent Convergence (PIC) 16:52 2022-03-26
Using PIC for Fast Failover 14:42 2022-03-26

21:34 MPLS Traffic Engineering Fast Reroute

MPLS Traffic Engineering Fast Reroute 13:06 2022-03-26
Automatic MPLS TE FRR Deployment 8:28 2022-03-26

32:22 Loop-Free Alternates (LFA)

Loop-Free Alternates Basics 10:57 2022-03-26
Remote LFA and Topology Independent LFA 11:54 2022-03-26
Discussion: LFA and Microloops 9:31 2022-03-26

Slide Decks

Why Should I Care About Networking 40M 2019-08-17
The Network Is Secure (and Other Fairy Tales) 22M 2023-03-19
The Role of Network Layers 22M 2019-06-17
Network Stack Addressing 11M 2019-11-04
Switching, Routing and Bridging 1.8M 2020-12-01
Routing Protocols 9.2M 2020-04-28
Advanced Routing Protocol Topics 2.7M 2022-02-15
Fast Failover 2.1M 2022-02-15

Textbooks and Other Books You Should Read

Learning about the basics of computer networking is no longer expensive. This section contains links to several high-quality open-source textbooks as well as must-read books by long-time networking engineers.

Computer Networking : Principles, Protocols and Practice
Computer Networks: A Systems Approach (Larry Peterson and Bruce Davie) (Peter L Dordal)
Computer Networking Problems and Solutions (Russ White and Ethan Banks)
Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (Radia Perlman)
Computer Networks (Andrew Tanenbaum)
Network Routing: Algorithms, Protocols, and Architectures (Deep Medhi, Karthik Ramasamy)
Network Algorithmics (George Varghese)

Even More Interesting Reading

Rise of the Stupid Network

A short essay describing some of the reasons Internet won against telephone networks

The Elements of Networking Style

A must-read for anyone interested in early history of the TCP/IP protocol stack

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