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Unformatted text preview: The Gorilla
Guide to…® Linux
Networking 101
Inside this Guide:
• Discover how Linux continues its march
toward world domination
• Learn basic Linux administration tips
• See how easy it can be to build your entire
network on a Linux foundation
• Find out how Cumulus Linux is your ticket to
networking freedom
David M. Davis ActualTech Media
Helping You Navigate
The Technology Jungle!
In Partnership With The Gorilla Guide To…
Linux Networking 101
Author
David M. Davis, ActualTech Media
Editors
Hilary Kirchner, Dream Write Creative, LLC
Christina Guthrie, Guthrie Writing & Editorial, LLC
Madison Emery, Cumulus Networks
Layout and Design
Scott D. Lowe, ActualTech Media
Copyright © 2017 by ActualTech Media. All rights reserved. No portion
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Entering the Jungle
Introduction: Six Reasons
You Need to Learn Linux ....................................................... 7 1. Linux is the future ........................................................................ 9
2. Linux is on everything .................................................................. 9
3. Linux is adaptable ....................................................................... 10
4. Linux has a strong community and ecosystem ........................... 10
5. Linux is fun!................................................................................ 10
6. Linux is open-source and sometimes free ................................... 10 Chapter 1: What Is Linux? .....................................................12 The History of Linux ...................................................................... 13
What Is an Operating System? ........................................................ 14
The Components that Comprise the Linux Operating System....... 15
What Is a Distribution? ................................................................... 16
Understanding User Space vs. Kernel Space ................................... 16
Benefits of Using Linux .................................................................. 18
How Is Linux Used in the Enterprise? ............................................ 21
Summary ........................................................................................ 22 Chapter 2: Basics of
Linux Administration........................................................... 23 Where Do I Get Linux? ................................................................... 23
How Do I Log In to Linux?............................................................. 24
How Do I Know What Type of Linux I Am Using? ........................ 26
Where Do I Find Things?................................................................ 27
Where Are the Applications, and How Do I Run Them? ............... 31
How Do I Install Applications?....................................................... 33 Linux Processes, Programs, and Services ........................................ 37
Importance of Linux Log Files ....................................................... 39
Users and Superusers ...................................................................... 40
Files and Permissions...................................................................... 42
Summary ........................................................................................ 44 Chapter 3: Basics of
Linux Network Administration .......................................... 45 Understanding Linux Network Interfaces ...................................... 45
MAC Addresses .............................................................................. 48
IP Addressing.................................................................................. 49
DHCP ....................................................................................... 51
DNS .......................................................................................... 53
Network Statistics and Counters .................................................... 55
How to Configure Network Interfaces ........................................... 57
Network Interface Bonding ....................................................... 60
Summary ........................................................................................ 63 Chapter 4: Understanding
Linux Internetworking......................................................... 64 Layer 2 vs. Layer 3 Internetworking ............................................... 66
Layer 2 Internetworking on Linux Systems .................................... 68
Bridging .................................................................................... 68
Spanning Tree ........................................................................... 70
Layer 3 Internetworking View on Linux Systems ........................... 73
Neighbor Table ......................................................................... 73
IP Routing ................................................................................. 74
Virtual LANs (VLANs) ................................................................... 76
Overlay Networks with VXLAN ..................................................... 79
Summary ........................................................................................ 82 Entering the Jungle iv Chapter 5: Cumulus Linux ................................................... 83 Network Command Line Utility (NCLU)...................................... 85
Building a Better Bridge ................................................................. 87
Two Links Are Better Than One ..................................................... 88
IP Fabrics Are Easy ......................................................................... 90
BGP EVPN—L3 Network Virtualization for Network Engineers .. 92 Next Steps .............................................................................. 95 Your Cumulus Linux Action Plan .................................................. 95 Entering the Jungle v Callouts Used in This Book
The Gorilla is the professorial sort
that enjoys helping people learn. In
the Schoolhouse callout, you’ll gain
insight into topics that may be
outside the main subject but that are
still important. This is a special place where readers
can learn a bit more about ancillary
topics presented in the book. When we have a great thought, we
express them through a series of
grunts in the Bright Idea section. Takes readers into the deep, dark
depths of a particular topic. Icons Used in This Book
Definition. Defines a word, phrase, or
concept.
Knowledge Check. Tests your knowledge of
what you’ve read.
Pay attention. We want to make sure you see
this!
GPS. We’ll help you navigate your knowledge
to the right place.
Watch out! Make sure you read this so you
don’t make a critical error! Introduction
Modern data centers are vastly different from legacy ones, and with
good reason. In the past, companies typically supported a handful of
critical monolithic applications, and the network was put in place
primarily to support just those applications. Once installed, the network
was left mostly untouched in many organizations. It consisted of
dedicated hardware-based routers and switches that, for the times,
performed their tasks of routing and switching packets quite well. The
routers and switches favored by many enterprises typically came from
one of the “big 3” networking vendors, but their products generally
included costly appliances made up of custom hardware and highly
proprietary software. That network gear was so specialized that an entire
ecosystem sprang up around it to provide training, education,
certification, consulting, software and support maintenance, and more.
Over time, the data center landscape has changed — and for the better,
particularly given that the application landscape has also morphed into
something radically different from what was seen in the past. The
number of business-critical applications is on the rise, and, unlike their
older stay-at-home cousins, modern applications are distributed
between on-premises infrastructure, between partner networks, and
across the public cloud. End user and company data moves around the
globe at light speed, and it’s happening constantly. New applications
are being built today and torn down tomorrow in favor of even newer
applications. Change is happening fast, and the network is adapting to
support these changes.
Thankfully, the specialized hardware that characterized legacy data
centers isn’t so necessary anymore. Today, networking needs are being
met using industry-standard switching/routing silicon, off-the-shelf
hardware, Intel CPUs, and the Linux operating system. This combination makes networking far more affordable, more scalable,
easier to learn, and more adaptable to the constantly changing needs of
the business. After all, the network’s sole purpose is to connect the users
with their applications and data, so it should do it as reliably, securely,
efficiently, and affordably as possible.
The key piece of the previous paragraph and the focus of this book is
this: Linux networking is the future for almost every use case. But to
leverage a Linux-based networking solution, you need to understand
Linux, and that’s where this book comes in. Definitions Abound!
If you don’t know what some of these words mean, don’t worry!
We’ll define them during your Linux 101 journey. By the end of this
book, you’ll be using these phrases in casual conversation! Six Reasons You Need to Learn Linux
What if you don’t know Linux and are asking yourself, “Is this book
really worth my time?” The short answer is a resounding YES, but to
back that up, let me give you six good reasons why you should invest
some of your time to learn Linux. 1. Linux is the future
Although Linux has been around for over 25 years, it has enjoyed a
continuous rise in business-critical usage, and many see Linux as being
the most popular operating system for the future. The reason as to why
Linux is the lingua franca of the modern data center relates to the points
below. 2. Linux is on everything
Linux runs more than two-thirds of the servers on the Internet, all
Android phones, most consumer network gear, such as NetGear and
Linksys devices, 99% of the top supercomputers in the world, many
Internet of Things (IoT) devices, Tesla cars, and even PlayStation
gaming consoles.
Introduction 9 3. Linux is adaptable
The very reason everything is on Linux is because it’s such an adaptable
operating system. Thanks to Linux’s modularity and open-source
nature, you can choose the pieces you need for your product or service
and develop any pieces that may not already exist. You can install tiny
versions of Linux for specialized use cases (such as operating water
sprinklers in the gorilla exhibit at the zoo), modify it to work on
appliances that route packets across a large enterprise network, or use it
as your desktop operating system. Your choices are practically endless. 4. Linux has a strong community and ecosystem
Linux has been so successful mainly because of the strong community
and ecosystem that surrounds it. There are Linux contributors
(developers who write code to make the product better); Linux forums
and communities; Linux instructors; Linux training options; Linux
blogs; Linux third-party tools; Linux distributions; Linux conferences;
and even Linux books such as this one! 5. Linux is fun!
Linux is a lot of fun because you can do just about anything with it.
Linux is commonly used in Internet of Things (IoT) projects; it runs on
tiny Raspberry Pi computers commonly used by hobbyists, and it even
makes a great operating system on your laptop or desktop computer.
More examples of the many uses of Linux are found throughout the
book. 6. Linux is open-source and sometimes free
Linux is open-source, meaning that the original source code is made
freely available and may be redistributed and modified. That said, there
are paid and fully supported commercial editions available, too. The
open nature of Linux has made it the adaptable OS of the future,
allowing it to run on everything, and has resulted in the creation of a
strong ecosystem. Introduction 10 Ready to start learning Linux?
Head to the first chapter in this Gorilla Guide and find out the answer
to the burning question: What is Linux? Introduction 11 Chapter 1
What Is Linux?
As you get started learning about Linux, you’ll likely have many of the
same questions that thousands of other people have had since the
beginning of Linux time. For that reason, we’ll start this chapter by
answering the most common questions about Linux.
By reading this chapter, you’ll find the answers to these questions:
1. What is an operating system?
2. What makes up
the Linux OS?
3. What makes
Linux
unique?
4. What are the b
enefits of using
Linux? Figure 1-1. Linus Torvalds,
principal author of the
Linux kernel, on
August 25, 1991, when he
announced his new Linux
kernel. “Hello everybody out there
using minix I’m doing a (free)
operating system (just a
hobby, won’t be big and
professional like gnu)…”
Photo by Krd (Own work) [CC BY-SA 3.0
( ) or CC
BY-SA 4.0 ( )], via Wikimedia Commons The History of Linux
Before we dive into Linux, let’s first take a step back in history. The
creation of Linux starts with another operating system known as UNIX,
which was first released in 1971. In 1983, the GNU Project (which stood
for “GNU’s not Unix”) was started to create a complete UNIXcompatible operating system. Efforts stalled, and the project was missing
a kernel. Around 1987, a UNIX-like operating system for students was
released called MINIX, but its licensing prevented it from being
distributed freely. Linus Torvalds (Figure 1-1) at the University of
Helsinki in Finland was frustrated by the licensing of MINIX and began
working on his own operating system kernel. His kernel, released in
1991, when combined with the GNU applications and open-source
licensing, became the Linux operating system we know today. What Is a Kernel, and What Does It Do?
The kernel is the special piece of the operating system
that controls the CPU hardware, allocates
memory, accesses data, schedules processes, runs
the applications, and protects them from each
other. It is the first program loaded on the computer when the computer
starts up. The most critical pieces of code in the kernel are loaded into
protected areas of memory so that they can't be overwritten by other
applications running in the operating system.
Since then, thousands of developers from around the world have
contributed to enhancing the Linux kernel as well as the many pieces of
software that make up the many different Linux distributions. Those
developers include volunteers as well as developers from commercial
companies. Today, the nonprofit Linux Foundation helps to create
standards, awareness, and advancements across many different Linux
projects. What Is Linux? 13 What Is an Operating System?
The short answer is that an operating system, or OS, is software that you
load on your hardware to make it “do things.” Without an operating
system, most hardware is useless. For example, you might have a Dell
computer that runs the Windows 10 operating system from which you
run your applications. You might have an iPhone that runs the iOS
operating system. You may also have an Apple MacBook that runs the
Apple macOS operating system. The operating systems on these
hardware platforms are what enable them to run applications, as shown
in Figure 1-2. APPLICATIONS
LIBRARIES SYSTEM
DAEMONS SHELLS TOOLS OPERATING SYSTEM
KERNEL
HARDWARE
Figure 1-2. How an operating system works with hardware and
applications What Is Linux? 14 The Components that Comprise the Linux
Operating System
Linux is an open-source OS that can be installed on a variety of different
types of hardware to allow you to develop software, run applications,
and more. At the heart of Linux is the kernel. Linux was developed in C
and assembly language to run on i386 personal computers, but it has
since been ported to more hardware than just about any other operating
system in history. Today, Linux is the most installed operating system
globally. In fact, the Space X Falcon 9 rocket and the International Space
Station both use Linux!
Linux is typically administered from a command line interface (CLI),
also known as a shell. Besides the kernel, which manages the hardware
and software processes, Linux distributions include a collection of Linux
software, such as device drivers for accessing and controlling hardware,
shared libraries, applications, and system daemons, which run the in
background and respond to network requests. Figure 1-3 shows an
example of what a common Linux distribution might look like.
Numerous programming languages are available for Linux, as well as
more than 70,000 different applications. Applications are installed from
packages, which contain the application itself and metadata about the
application. Definition: Metadata
Metadata is data about data. In essence, metadata describes the
kind of information that an underlying data set will store. Take, for
instance, a file system on a computer. When you view a directory
listing, you see the file name, file size, create date, last modified date,
and so forth. These are basic examples of metadata associated with
each object in that directory. What Is Linux? 15 What is a Linux Daemon?
A system daemon in Linux is typically a background
system process that awaits a specific set of
conditions before jumping into action. For
example, your Linux system may have a daemon
called sshd, which stands for Secure Shell daemon.
This system daemon runs in the background and accepts authorized
incoming requests to log into the Linux host. System daemons do not
interact with users and are not typically under the direct control of
users, but rather of the system itself. What Is a Distribution?
Often called a “distro,” a Linux distribution is the combination of specific
versions of the Linux kernel with other libraries, system daemons,
development tools, applications, packaging, and life-cycle management
tools that are compatible with each other and tested for interoperability.
The most common way that people acquire Linux today is by
downloading one of the many different Linux distributions.
Distributions are available not just for servers, desktop, and laptop
computers, but also for a huge variety of more specialized devices that
run Linux. Examples of Linux distributions are Ubuntu, Debian, Fedora,
openSUSE, and Cumulus Linux. Understanding User Space vs. Kernel
Space
Operating systems all execute their kernel in protected and restricted
memory that is called kernel space (see Figure 1-4) to prevent the kernel
from terminating and crashing the system. What Is Linux? 16 APPLICATIONS
DATABASE, WEB SERVER, NETWORK MONITOR, ETC. LIBRARIES SYSTEM
DAEMONS SHELLS TOOLS LINUX KERNEL
SCHEDULER, DRIVERS, SECURITY, NETWORKING Figure 1-3. Example of a common Linux distribution When a user runs an application or tool, that application or tool
executes in what is called user space. This distinction is critical.
Applications can come from a variety of sources, may be poorly
developed, or originate unknown sources.
By running these
applications separate from kernel space, they can’t tamper with the
kernel resources and cause the system to panic (crash).
All applica...
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