linux-nameserver.html

Linus guide, Linus guide, Linus guide,

under that domain (like, for the penguincomputing.com domain, the
nameservers would have the information for what IP address
pasta.penguincomputing.com gets and the one that
antarctica.penguincomputing.com gets). Here's an example of a domain's
records:</P>

<PRE>
@	IN	SOA	penguincomputing.com.	root.penguincomputing.com.
(
			1998082403	;	serial
			4H		;	refresh, seconds
			2H		;	retry, seconds
			1W		;	expire, seconds
			1D	)	;	minimum, seconds
		NS	pasta.penguincomputing.com.
		NS	rice.penguincomputing.com.
		MX	10 penguincomputing.com. ;  Primary Mail Exchanger

localhost	A	127.0.0.1
router		A	140.174.204.2

penguincomputing.com.	A	209.81.10.250
ns		A	209.81.10.250
www		A	209.81.10.250
ftp		CNAME	penguincomputing.com.
mail		CNAME	penguincomputing.com.
news		CNAME	penguincomputing.com.
pasta		CNAME	penguincomputing.com.
slashdot	CNAME	penguincomputing.com.
rice		CNAME	antarctica.penguincomputing.com.
antarctica	A	209.81.10.252
antarctic	CNAME	antarctica.penguincomputing.com.
www.antarctic	CNAME	antarctica.penguincomputing.com.
www.antarctica	CNAME	antarctica.penguincomputing.com.
zork		A	209.81.10.253
tux		A	209.81.10.146
xfce		A	209.81.10.252

@		TXT	"Penguin Computing"
@		HINFO	Linux 2.0.34
</PRE>

<P>There's a pretty weird syntax to be used for these zone files. I never
would have figured it out on my own had I not read the Linux DNS HOWTO
document. Basically, it specifies information about all the machines in
the domain, and it contains information about the domain itself, such as
the type of machine the server is running on.</P>

<P>I'll start explaining what all the stuff does. In the first line, it's
saying that this file specifies the zones for the penguincomputing.com
domain, and to send anything about the domain to
<I>[e-mail]</I>. Since the &quot;@&quot; character has
special significance in these <B>zone files</B>, the username (root) and
machine name (penguincomputing.com) have to be separated by a dot. I guess
BIND just knows how to split it up. That's how you fill in stuff for your
domain as well.</P>

<P>The line with the comment &quot;serial&quot; shows the serial number of
that domain. The syntax is YYYYMMDDRR; that is, a four digit year, two
digit month in numerical form, two digit day format, and a two digit
revision number. In this example (1998082403), it shows that the zone file
was last modified on August 24, 1998. It's the third revision for that
day. When you're changing anything in the file, make sure to increase the
revision number by one if the previous change was on the same day. If I
were to change the IP of one of the hosts, I would make the last two
numbers, currently 03, to 04.</P>

<P>The next few lines show times for certain functions such as refreshing,
retrying, and expiring the information. I'm not <I>absolutely</I> sure,
but my best guess is that H stands for hour, D stands for day, and W
stands for week.</P>

<P>The &quot;NS&quot; line indicates all the nameservers for that
particular domain, including the one this information is on. This
information has to match what has been registered with InterNIC. For the
hostnames of the nameservers, remember to add a dot at the end. If you
don't, it will add the hostname to the current domain. For example, if you
forgot the dot at the end of pasta.penguincomputing.com, you would end up
with the nameserver being pasta.penguincomputing.com.penguincomputing.com,
which is obviously not what it's supposed to be. Watch out for this.</P>

<P>The MX file is the <I>M</I>ail e<I>X</I>change record, so that mail can
get through to the domain. There should also be an entry in
/etc/sendmail.cw to allow messages coming in from that domain (assuming
you're using Sendmail, the default on many Linux systems, for mail
transfer).</P>

<P>The next couple of lines point to the local loopback (127.0.0.1), which
all Linux systems should have even if they aren't connected to a network.
The &quot;router&quot; line points to the IP address of where the
machine's Internet connection is. I'm not sure if it's really necessary
but I was playing it safe back then and trying to copy the example from
the DNS HOWTO as closely as possible.</P>

<P>The rest of the entries use either A (address) or CNAME (Canonical
Name) to point hostnames to IP addresses. Note that hostnames can be
mapped to other hostnames, or they can be mapped to IP addresses. Use A to
map a name to an IP address, and CNAME to map a hostname to another
hostname (which must be mapped to another IP address).</P>

<A NAME="localhost"></A>
<H4><A NAME="8">Localhost</A></H4>

<P>The file for mapping localhost is pretty simple. Not much explanation
needed. Of course, if you want to copy and paste, be sure you make the 
proper changes.</P>

<PRE>
@	IN	SOA	penguincomputing.com root.penguincomputing.com (
			1998072401	;	Serial number
			3H		;	Refresh
			1H		;	Retry
			604800		;	Expire
			86400)		;	Minimum TTL

		NS	pasta.penguincomputing.com.
		NS	rice.penguincomputing.com.

1		PTR	localhost.
</PRE>

<A NAME="reverse"></A>
<H4><A NAME="9">Reverse Mapping</A></H4>

<P>This file looks similar to the zone file for the domains, but it
provides the opposite function. It points IP addresses to hostnames (as
opposed to vice versa), because many servers on the Internet do this thing
called reverse lookup on the IP address of your hostname to make sure that
you're not doing anything sneaky.</P>

<P>This is for the zone &quot;209.81.10&quot; specified in the sample
configuration file. Note that my example is not complete, nor does it work
in reality, because Penguin Computing doesn't own the whole block of
&quot;209.81.10.*&quot;. But this is how you'd fill in a file to resolve
your IP addresses to hostnames <I>if</I> you owned the entire block of IP
addresses.</P>

<PRE>
@               IN      SOA     penguincomputing.com.	root.penguincomputing.com. (
                                1998072002       ; Serial
                                4H   	; Refresh
                                2H    	; Retry
                                604800  ; Expire
                                86400)  ; Minimum TTL
                        NS      pasta.penguincomputing.com.
                        NS      rice.penguincomputing.com.
;
;       Servers
;
250     PTR	pasta.penguincomputing.com.
250     PTR	penguincomputing.com.
250	PTR	ftp.penguincomputing.com.
250	PTR	www.penguincomputing.com.
250	PTR	mail.penguincomputing.com.
251     PTR	rice.penguincomputing.com.

;
;       Workstations
;
252	PTR	antarctica.penguincomputing.com.
252	PTR	antarctic.penguincomputing.com.
</PRE>

<P>If you were to fill in an actual zone file like this, it's necessary to
fill in <I>all</I> the entries in your block of IP addresses, from 1 to
255. For something like that you may want to assign the task to anyone who
looks bored.</P>

<P>So what should you do if you only own a domain but not the block of IP
addresses that it's part of? Ask the people who are in charge of that
block of IP addresses to map your IP addresses to their respective
hostnames for you.</P>

<A NAME="resources"></A>
<H3><A NAME="10">Resources</A></H3>

<P>The following is a list of resources I referred to in order to help me
set up a nameserver for myself and write this document.</P>

<OL>
<LI><A HREF="http://www.linuxdoc.org/HOWTO/DNS-HOWTO.html" TARGET="_top">Linux DNS HOWTO</A></LI>
<LI><A HREF="http://www.isc.org/bind8/config.html" TARGET="_top">BIND Configuration File Syntax</A></LI>
</OL>

<HR>

<P>Comments, questions, suggestions? Send them to <A
HREF="mailto:[e-mail]">[e-mail]</A>.</P>

<HR>

<P><B><FONT SIZE="-1">Copyright &copy; 1997-1998 <A
HREF="mailto:[e-mail]">Joshua Go ([e-mail])</A>. All
rights reserved. Permission to use, distribute, and copy this document is
hereby granted. You may modify this document as long as credit to me is
given.</FONT></B></P>

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