Networking for Systems Administrators

181 Pages·2015·0.78 MB·English

by  Michael W Lucas

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About the Author
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Acknowledgements
The people who most deserve thanks for this book are the folks who struggled through me
learning networking as I stood between them and what they wanted to accomplish. Every
one of you brought me some horrible issue that educated me even as you ranted and cried
and begged for me to fix the problem. I learn slowly, and you suffered for it. Thank you.
Fortunately, suffering builds character, so you got something out of it and I don’t have to
feel too bad.
This book had a crew of excellent technical reviewers. Some of them have an
understanding of networking that crushes mine. Others knew nothing about networking,
but were able to tell me when I confused them. Both are invaluable. They are, in
alphabetical order: Alexiei Bottino, Donald Cooley, Fred Crowson, Michael Dexter,
Dominik Douville-Bélanger, Edwin Groothuis, Josh Grosse, Bryan Irvine, Chris Josephes,
Frank Moore, Kurt Mosiejczuk, Scott Murphy, Chris Parr, Martin Pugh, Mike O’Connor,
A.J. Reese, Amanda Robinson, Jim Salter, Justin Sherrill, Carsten Strotmann, Grant
Taylor, and Giovanni Torres. You all had excellent advice and lots of really good
recommendations. Those recommendations would have made this book four times longer,
but they really were excellent.
This book was made possible through hardware purchased from iX Systems
(http://www.ixsystems.com). Well, not exactly possible. More like “a heck of a lot easier
than trying to keep a maddening mishmash of recycled debris booting without bursting
into great fountains of toxic flame.”
And a special thanks to the people who’ve thrown a few bucks into my Tilted Windmill
Press tip jar. You folks make writing for a living a lot more realistic.
For Liz
Chapter 0: The Problem
Dear systems administrators: the firewall people don’t want to talk to you, either.
It’s nothing personal. We all share the goal of delivering service to users, but once you
break that goal down into meaningful parts our teams completely diverge. Our tools differ.
Our equipment differs. We even think differently. Sysadmins care about bytes, network
administrators measure everything in bits. Network equipment might be built on computer
hardware, but it’s very specialized hardware that doesn’t have any of the tools that systems
administrators take for granted. Servers have network interfaces, but not nearly enough of
them to do anything interesting.
Neither one understands how the other can possibly perform their job without the basic
tools their platform offers.
Both roles require a high degree of specialization, especially in modern enterprises.
The firewall administrator doesn’t have time to dig into the specifics of the latest version
of whatever operating system you’re using. You don’t have time to figure out why the
newest version of the big firewall is mangling your carefully-crafted HTTP headers.
This is all complicated stuff. While I spend more time in systems administration than
network engineering, I’ve filled both roles in the last twenty years. Each time I switch
from one hat to the other I spend a few weeks catching up with the latest annoyances.
The end result? The network folks blame the servers. The server people blame the
network. Often the blame gets personal. “It’s the sysadmin’s fault!” “If the firewall crew
knew what they were doing, this wouldn’t happen!” Meanwhile the helpdesk folks—
correctly—blame everyone for not making customers stop whining. I’ve been in
organizations where the only thing that prevented open warfare between IT teams was a
shortage of sharp stabby objects.
Even in the best environments, differing expertise and priorities make both jobs more
difficult than they have to be. Many organizations avoid this warfare by applying trouble
tickets, workflow, and meetings. Lots and lots of brain-numbing meetings.
It doesn’t have to be this way.
A systems administrator can’t learn the ins and outs of each version of networking gear
any more than a network administrator can learn the ins and out of the latest generation of
your operating system. Neither one of you has the time to keep up with this constantly
changing information on top of your own area of expertise.
A network administrator can—and should—learn the basics of how a server operates.
Every network administrator should understand the basics of user access control and
privileges, processes, services and daemons, basic installation and removal of software,
and so on. But this information varies wildly between operating system platforms.
Sometimes it’s a language difference—Unix-like operating systems have daemons, while
Microsoft systems have services. Sometimes even closely related operating systems have
very different ways to handle similar tasks, such as the myriad ways of installing software
on various Unix-like operating systems, or even on one operating system!1 The network
administrator might learn the basics of the operating systems in your organization, but this
knowledge won’t carry forward to her next assignment.
Systems administrators can learn the basics of networking, however. And this
knowledge will serve you no matter what organization you work with or what sort of
network gear your organization uses. You don’t need to know how to configure a router or
a firewall or any other network device—they’re all ephemeral anyway.
But basic TCP/IP knowledge endures. While people add new protocols all the time,
these are incremental changes and easily mastered. It’s much easier to teach a systems
administrator the basics of networking than it is to teach a network administrator the
basics of systems administration, and that knowledge will last your entire career.
Understanding the network saves you time. You won’t wonder if a network change has
been made—you’ll check it yourself. You won’t call to see if a problem is inside your
network—you’ll look and find out. You’ll quickly determine if problems exist on your
systems, on your network, or outside your network.
Most network administrators quickly learn which systems administrators understand
basic networking and which don’t. When I’m a network administrator I’m happy to work
with the sysadmins that don’t ask me if I’ve opened that firewall port or if there’s a
problem between here and our office in Farawayistan. Being asked “When will the link to
Farawayistan be fixed?” might be harder to answer, but it does save a loop in the
conversation.
If I’m a network administrator with a whole stack of issues to resolve, but I know that
you speak from evidence when you say “This traffic isn’t reaching my server,” I’ll address
your problem before everyone else’s. There’s a really good chance that I can fix your
problem quickly because you provide me with actual information. If my phone is ringing
like mad and everything seems to have collapsed, resolving your problem might solve
problems for a whole bunch of other people.
Make yourself the most valued member of your systems administration team. Take a
couple hours to read this book, learn a little networking, and become a bridge to other
critical IT groups.
We’ll start by discussing network principles, and then go into detail on how to view or
use those principles on multiple operating systems. This book covers Windows, Linux
(CentOS and Debian), and BSD platforms, but the principles and tools run on just about
any modern networked operating system, including portable devices like phones and
tablets.
Who Should Read This Book?
Every sysadmin, database admin, web admin, developer, and computing professional
should understand the basic principles of networking. This book grounds you in modern
TCP/IP without demanding a month’s dedicated study. Understanding the network will
empower you to identify the real source of problems, solve your own problems more
quickly, and make better requests of your team members.
This book is also for network administrators who need to educate others in their team
about the essentials of networking. After a few years, a network administrator’s
understanding of TCP/IP turns into an interconnected morass of window scaling and
sequence numbers and malformed packets. Someone asks what a port is, and moments
later you’re explaining SYN floods and the questioner has learned the vital lesson of
“never ask the network administrator anything.” (This trait isn’t exclusive to network
administrators—it’s endemic in the IT industry. Ask a database administrator to explain
databases sometime.2) That stuff is all vital to a network administrator’s job, but the
average user doesn’t need to understand it. You can use this book to explain only what the
average sysadmin absolutely must know about TCP/IP.