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[Chapter 4] 4.6 Informing the Users

[Chapter 4] 4.6 Informing the Users

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[Chapter 4] 4.6 Informing the Users
Default gateway: (almond.nuts.com)
Broadcast address:
Domain name:
Name servers: (almond.nuts.com) (pack.plant.nuts.com)
Routing protocol:
Routing Information Protocol (RIP)
Mail server: (almond.nuts.com)
Mail relay: (almond.nuts.com)
Print server: (pecan.nuts.com)
NFS server: (filbert.nuts.com)
A similar sheet prepared for almond (see below) varies slightly from the planning sheet for peanut.
The names and address are different, of course, but the real differences are caused by the fact that
almond is a gateway. As a gateway, almond has more than one network interface, and each interface
requires its own configuration. Each interface has its own address and can have its own name, subnet
mask, and routing protocol.
almond (
mil-gw (
IP address:

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[Chapter 4] 4.6 Informing the Users
Subnet mask: (
default (
Default gateway:
Broadcast address: (
default (
Domain name:
Name servers: (almond.nuts.com) (pack.plant.nuts.com)
Routing protocol:
Routing Information Protocol (RIP) (
Border Gateway Protocol (BGP) (
Print server: (pecan.nuts.com)
NFS server: (filbert.nuts.com)
We use the information from these planning sheets to configure the systems in subsequent chapters.
You may, however, want to format your planning sheets differently. In this book we configure the
system directly. We use the configuration commands ourselves so that we can understand and master
them. In reality many basic configuration tasks are performed by a network configuration script
during the initial operating system installation. You may want to format your planning sheet to be
compatible with the prompts of that script. One such script is netconfig, which is used on Linux

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[Chapter 4] 4.6 Informing the Users

Previous: 4.5 Other
4.5 Other Services

TCP/IP Network
Book Index

Next: 4.7 netconfig
4.7 netconfig

[ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ]

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[Chapter 4] 4.5 Other Services

Previous: 4.4 Planning
Naming Service

Chapter 4
Getting Started

Next: 4.6 Informing the

4.5 Other Services
Three services that are used on many networks are file servers, print servers, and mail servers. The
purpose of these services and the protocols they are built on is discussed in Chapter 3. In this section
we investigate what information must be passed to the users so that the client systems can be
successfully configured, and how the network administrator determines that information.

4.5.1 File servers
At a minimum the user needs to know the hostnames of the network file servers. Using the names and
the showmount command, the user can determine what filesystems are being offer by the servers and
who is permitted to use those filesystems. [8] Without at least the hostname, the user would have to
guess which system offered file service.
[8] See the showmount command in Chapter 9.
A better approach is to give users information that also includes what filesystems are being offered
and who should use those filesystems. For example, if the UNIX man pages are made available from
a central server, the users should be informed not to install the man pages on their local disk drives
and they should be told exactly how to access the centrally supported files.

4.5.2 Print servers
Whether printers are shared using lp, lpd, or NFS, the basic information needed to configure the print
server's clients is the same: the hostname and IP address of the print server, and the name of the
printer. Printer security may also require that the user be given a username and password to access the
This is the only information needed to configure the client. However, you probably will want to
provide your users with additional information about the features, location and administration of
shared printers.

4.5.3 Planning Your Mail System
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[Chapter 4] 4.5 Other Services

TCP/IP provides the tools you need to create a reliable, flexible electronic mail system. Servers are
one of the tools that improve reliability. It is possible to create a peer-to-peer email network in which
every end system directly sends and receives its own mail. However, relying on every system to
deliver and collect the mail requires that every system be properly administered and consistently up
and running. This isn't practical, because many small systems are offline for large portions of the day.
Most networks use servers so that only a few systems need to be properly configured and operational
for the mail to go through.
The terminology that describes email servers is confusing because all of the server functions usually
occur in one computer, and all of the terms are used interchangeably to refer to that system. In this
text we differentiate between these functions, but we expect you will do all of these tasks on one
UNIX system running sendmail. We use these terms in the following manner:
Mail server
The mail server collects incoming mail for other computers on the network. It supports
interactive logins as well as POP or IMAP so that users can read their mail as they see fit.
Mail relay
A mail relay is a host that forwards mail between internal systems and from internal systems to
remote hosts. Mail relays allow internal systems to have simple mail configurations because
only the relay host needs to have software to handle special mail addressing schemes and
Mail gateway
A mail gateway is a system that forwards email between dissimilar systems. You don't need a
gateway to go from one Internet host to another because both systems use SMTP. You do need
a gateway to go from SMTP to X.400 or to a proprietary mailer. In a pure TCP/IP network, this
function is not needed.
The mail server is the most important component of a reliable system because it eliminates reliance on
the user's system. A centrally controlled, professionally operated server collects the mail regardless of
whether or not the end system is operational.
The relay host also contributes to the reliability of the email system. If mail cannot be immediately
delivered by the relay host, it is queued and processed later. An end system also queues mail, but if it
is shut down no attempts can be made to deliver queued mail until the system is back online. The mail
server and the mail relay are operated 24 hours a day.
The design of most TCP/IP email networks is based on the following guidelines:

Use a mail server to collect mail, and POP or IMAP to deliver the mail.
Use a mail relay host to forward mail. Implement a simplified email address scheme on the
relay host.

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