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: http://rtm-cs.sinp.msu.ru/manual/howto/DNS-HOWTO.html
Дата изменения: Thu May 4 19:11:19 2000 Дата индексирования: Mon Oct 1 20:44:59 2012 Кодировка: |
janl@math.uio.no
Keywords: DNS, bind, bind-4, bind-8, named, dialup, ppp, slip, isdn, Internet, domain, name, hosts, resolving, caching.
This document is part of the Linux Documentation Project.
(C)opyright 1995-1999 Nicolai Langfeldt. Do not modify without amending copyright, distribute freely but retain copyright message.
I want to thank Arnt Gulbrandsen whom I cause to suffer through the drafts to this work and whom provided many useful suggestions. I also want to thank the numerous people that have e-mailed suggestions and notes.
This will never be a finished document, please send me mail about your problems and successes, it can make this a better HOWTO. So please send comments and/or questions or money to janl@math.uio.no. If you send e-mail and want an answer please show the simple courtesy of making sure that the return address is correct and working. Also, please read the QnA section before mailing me. Another thing, I can only understand Norwegian and English.
If you want to translate this HOWTO please notify me so I can keep track of what languages it has been published in, and also I can notify you when the HOWTO has been updated.
This HOWTO is dedicated to Anne Line Norheim Langfeldt. Though she will probably never read it since she's not that kind of girl.
What this is and isn't.
DNS is is the Domain Name System. DNS converts machine names to
the IP addresses that all machines on the net have. It maps from name
to address and from address to name, and some other things. This
HOWTO documents how to define such mappings using a Linux system. A
mapping is simply a association between two things, in this case a
machine name, like ftp.linux.org, and the machines IP number (or
address) 199.249.150.4.
DNS is, to the uninitiated (you ;-), one of the more opaque areas of network administration. This HOWTO will try to make a few things clearer. It describes how to set up a simple DNS name server. Starting with a caching only server and going on to setting up a primary DNS server for a domain. For more complex setups you can check the QnA section of this document. If it's not described there you will need to read the Real Documentation. I'll get back to what this Real Documentation consists of in the last chapter.
Before you start on this you should configure your machine so that
you can telnet in and out of it, and successfully make all kinds of
connections to the net, and you should especially be able to do
telnet 127.0.0.1 and get your own machine (test it now!). You
also need a good /etc/nsswitch.conf (or
/etc/host.conf), /etc/resolv.conf and
/etc/hosts files as a starting point, since I will not
explain their function here. If you don't already have all this set
up and working the NET-3-HOWTO and/or the PPP-HOWTO explains how to
set it up. Read them.
When I say `your machine' I mean the machine you are trying to set up DNS on. Not any other machine you might have that's involved in your networking effort.
I assume you're not behind any kind of firewall that blocks name queries. If you are you will need a special configuration, see the section on QnA.
Name serving on Unix is done by a program called named. This
is a part of the ``bind'' package which is coordinated by Paul Vixie
for The Internet Software Consortium. Named is included in most
Linux distributions and is usually installed as
/usr/sbin/named. If you have a named you can probably use
it; if you don't have one you can get a binary off a Linux ftp site,
or get the latest and greatest source from
ftp.isc.org:/isc/bind/src/cur/bind-8/. This HOWTO is about
bind version 8. The old version of the HOWTO, about bind 4 is still
available at
http://www.math.uio.no/~janl/DNS/ in case you use bind 4. If
the named man page talks about (at the very end, the FILES section)
named.conf you have bind 8, if it talks about named.boot you
have bind 4. If you have 4 and are security conscious you really
ought to upgrade to a recent 8.
DNS is a net-wide database. Take care about what you put into it. If you put junk into it, you, and others will get junk out of it. Keep your DNS tidy and consistent and you will get good service from it. Learn to use it, admin it, debug it and you will be another good admin keeping the net from falling to it's knees by mismanagement.
In this document I state flatly a couple of things that are not completely true (they are at least half truths though). All in the interest of simplification. Things will (probably ;-) work if you believe what I say.
Tip: Make backup copies of all the files I instruct you to change if you already have them, so if after going through this nothing works you can get it back to your old, working state.
A first stab at DNS config, very useful for dialup users.
A caching only name server will find the answer to name queries and remember the answer the next time you need it. This will shorten the waiting time the next time significantly, especially if you're on a slow connection.
First you need a file called /etc/named.conf. This is
read when named starts. For now it should simply contain:
// Config file for caching only name server
options {
directory "/var/named";
// Uncommenting this might help if you have to go through a
// firewall and things are not working out:
// query-source port 53;
};
zone "." {
type hint;
file "root.hints";
};
zone "0.0.127.in-addr.arpa" {
type master;
file "pz/127.0.0";
};
The `directory' line tells named where to look for files. All
files named subsequently will be relative to this. Thus pz
is a directory under /var/named, i.e.,
/var/named/pz. /var/named is the right directory
according to the Linux File system Standard.
The file named /var/named/root.hints is named in this.
/var/named/root.hints should contain this:
; ; There might be opening comments here if you already have this file. ; If not don't worry. ; . 6D IN NS G.ROOT-SERVERS.NET. . 6D IN NS J.ROOT-SERVERS.NET. . 6D IN NS K.ROOT-SERVERS.NET. . 6D IN NS L.ROOT-SERVERS.NET. . 6D IN NS M.ROOT-SERVERS.NET. . 6D IN NS A.ROOT-SERVERS.NET. . 6D IN NS H.ROOT-SERVERS.NET. . 6D IN NS B.ROOT-SERVERS.NET. . 6D IN NS C.ROOT-SERVERS.NET. . 6D IN NS D.ROOT-SERVERS.NET. . 6D IN NS E.ROOT-SERVERS.NET. . 6D IN NS I.ROOT-SERVERS.NET. . 6D IN NS F.ROOT-SERVERS.NET. G.ROOT-SERVERS.NET. 5w6d16h IN A 192.112.36.4 J.ROOT-SERVERS.NET. 5w6d16h IN A 198.41.0.10 K.ROOT-SERVERS.NET. 5w6d16h IN A 193.0.14.129 L.ROOT-SERVERS.NET. 5w6d16h IN A 198.32.64.12 M.ROOT-SERVERS.NET. 5w6d16h IN A 202.12.27.33 A.ROOT-SERVERS.NET. 5w6d16h IN A 198.41.0.4 H.ROOT-SERVERS.NET. 5w6d16h IN A 128.63.2.53 B.ROOT-SERVERS.NET. 5w6d16h IN A 128.9.0.107 C.ROOT-SERVERS.NET. 5w6d16h IN A 192.33.4.12 D.ROOT-SERVERS.NET. 5w6d16h IN A 128.8.10.90 E.ROOT-SERVERS.NET. 5w6d16h IN A 192.203.230.10 I.ROOT-SERVERS.NET. 5w6d16h IN A 192.36.148.17 F.ROOT-SERVERS.NET. 5w6d16h IN A 192.5.5.241
The file describes the root name servers in the world. This changes over time and must be maintained. See the maintenance section for how to keep it up to date.
The next section in named.conf is the last zone. I will
explain its use in a later chapter, for now just make this a file
named 127.0.0 in the subdirectory pz:
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
1 ; Serial
8H ; Refresh
2H ; Retry
1W ; Expire
1D) ; Minimum TTL
NS ns.linux.bogus.
1 PTR localhost.
Next, you need a /etc/resolv.conf looking something like
this:
search subdomain.your-domain.edu your-domain.edu nameserver 127.0.0.1
The `search' line specifies what domains should be searched
for any host names you want to connect to. The `nameserver' line
specifies the address of your nameserver, in this case your own
machine since that is where your named runs (127.0.0.1 is right, no
matter if your machine has an other address too). If you want to list
several name servers put in one `nameserver' line for
each. (Note: Named never reads this file, the resolver that uses named
does.)
To illustrate what this file does: If a client tries to look up
foo, then foo.subdomain.your-domain.edu is tried
first, then foo.your-fomain.edu, finally foo. If a
client tries to look up sunsite.unc.edu,
sunsite.unc.edu.subdomain.your-domain.edu is tried first
(yes, it's silly, but that's the way it works), then
sunsite.unc.edu.your-domain.edu, and finally
sunsite.unc.edu. You may not want to put in too many domains
in the search line, it takes time to search them all.
The example assumes you belong in the domain
subdomain.your-domain.edu, your machine then, is probably
called your-machine.subdomain.your-domain.edu. The search
line should not contain your TLD (Top Level Domain, `edu' in this
case). If you frequently need to connect to hosts in another domain
you can add that domain to the search line like this:
search subdomain.your-domain.edu your-domain.edu other-domain.com
and so on. Obviously you need to put real domain names in instead. Please note the lack of periods at the end of the domain names. This is important, please note the lack of periods at the end of the domain names.
Next, depending on your libc version you either need to fix
/etc/nsswitch.conf or /etc/host.conf. If you
already have nsswitch.conf that's what we'll fix, if not, we'll
fix host.conf.
/etc/nsswitch.conf
This is a long file specifying where to get different kinds of data
types, from what file or database. It usually contains helpful
comments at the top, which you should consider reading. After that
find the line starting with `hosts:', it should read
hosts: files dns
If there is no line starting with `hosts:' then put in the one
above. It says that programs should first look in the
/etc/hosts file, then check DNS according to
resolv.conf.
/etc/host.conf
It probably contains several lines, one should start with
order and it should look like this:
order hosts,bind
If there is no `order' line you should add one. It tells the
host name resolving routines to first look in /etc/hosts,
then ask the name server (which you in resolv.conf said is at
127.0.0.1).
After all this it's time to start named. If you're using a dialup
connection connect first. Type `ndc start', and press return, no
options. If that does not work try `/usr/sbin/ndc start'
instead. If that back-fires see the
QnA
section. If you view your syslog message file (usually called
/var/adm/messages, but another directory to look in is
/var/log and another file to look in is syslog) while
starting named (do tail -f /var/log/messages) you should see
something like:
(the lines ending in \ continue on the next line)
Feb 15 01:26:17 roke named[6091]: starting. named 8.1.1 Sat Feb 14 \
00:18:20 MET 1998 ^Ijanl@roke.uio.no:/var/tmp/bind-8.1.1/src/bin/named
Feb 15 01:26:17 roke named[6091]: cache zone "" (IN) loaded (serial 0)
Feb 15 01:26:17 roke named[6091]: master zone "0.0.127.in-addr.arpa" \
(IN) loaded (serial 1)
Feb 15 01:26:17 roke named[6091]: listening [127.0.0.1].53 (lo)
Feb 15 01:26:17 roke named[6091]: listening [129.240.230.92].53 (ippp0)
Feb 15 01:26:17 roke named[6091]: Forwarding source address is [0.0.0.0].1040
Feb 15 01:26:17 roke named[6092]: Ready to answer queries.
If there are any messages about errors then there is a mistake. Named will name the file it is in (one of named.conf and root.hints I hope :-) Kill named and go back and check the file.
Now you can test your setup. Start nslookup to examine your work.
$ nslookup
Default Server: localhost
Address: 127.0.0.1
>
If that's what you get it's working. We hope. Anything else, go
back and check everything. Each time you change the named.conf
file you need to restart named using the ndc restart command.
Now you can enter a query. Try looking up some machine close to
you. pat.uio.no is close to me, at the University of Oslo:
> pat.uio.no
Server: localhost
Address: 127.0.0.1
Name: pat.uio.no
Address: 129.240.130.16
nslookup now asked your named to look for the machine
pat.uio.no. It then contacted one of the name server machines
named in your root.hints file, and asked its way from there.
It might take tiny while before you get the result as it may need to
search all the domains you named in /etc/resolv.conf.
If you ask the same again you get this:
> pat.uio.no
Server: localhost
Address: 127.0.0.1
Non-authoritative answer:
Name: pat.uio.no
Address: 129.240.2.50
Note the ``Non-authoritative answer:'' line we got this time
around. That means that named did not go out on the network to ask
this time, the information is in the cache now. But the cached
information might be out of date (stale). So you are informed of
this (very slight) possibility by it saying `Non-authorative
answer:'. When nslookup says this the second time you ask for a
host it's a sure sign that named caches the information and that it's
working. You exit nslookup by giving the command `exit'.
In large, well organized, academic or ISP (Internet Service
Provider) networks you will sometimes find that the network people has
set up a forwarder hierarchy of DNS servers which helps lighten the
internal network load and on the outside servers as well. It's not
easy to know if you're inside such a network or not. It is however
not important and by using the DNS server of your network provider as
a ``forwarder'' you can make the responses to queries faster and less
of a load on your network. If you use a modem this can be quite a
win. For the sake of this example we assume that your network
provider has two name servers they want you to use, with IP numbers
10.0.0.1 and 10.1.0.1. Then, in your named.conf file,
inside the opening section called ``options'' insert these lines:
forward first;
forwarders {
10.0.0.1;
10.1.0.1;
};
Restart your nameserver and test it with nslookup. Should work fine.
Now you know how to set up a caching named. Take a beer, milk, or whatever you prefer to celebrate it.
How to set up your own domain.
Before we really start this section I'm going to serve you
some theory on and an example of how DNS works. And you're going to
read it because it's good for you. If you don't want to you should at
least skim it very quickly. Stop skimming when you get to what should
go in your named.conf file.
DNS is a hierarchical, tree structured, system. The top is written
`.' and pronounced `root'. Under . there are a number of
Top Level Domains (TLDs), the best known ones are ORG, COM,
EDU and NET, but there are many more. Just like a tree it
has a root and it branches out. If you have any computer science
background you will recognize DNS as a search tree, and you will be
able to find nodes, leaf nodes and edges.
When looking for a machine the query proceeds recursively into the
hierarchy starting at the top. If you want to find out the address of
prep.ai.mit.edu your name server has to find a name server that
serves edu. It asks a . server (it already knows the .
servers, that's what the root.hints file is for), the .
server gives a list of edu servers:
$ nslookup
Default Server: localhost
Address: 127.0.0.1
Start asking a root server:
> server c.root-servers.net.
Default Server: c.root-servers.net
Address: 192.33.4.12
Set the Query type to NS (name server records):
> set q=ns
Ask about edu:
> edu.
The trailing . here is significant, it tells nslookup we're asking
that edu is right under . (and not under any of our
search domains, it speeds the search).
edu nameserver = A.ROOT-SERVERS.NET
edu nameserver = H.ROOT-SERVERS.NET
edu nameserver = B.ROOT-SERVERS.NET
edu nameserver = C.ROOT-SERVERS.NET
edu nameserver = D.ROOT-SERVERS.NET
edu nameserver = E.ROOT-SERVERS.NET
edu nameserver = I.ROOT-SERVERS.NET
edu nameserver = F.ROOT-SERVERS.NET
edu nameserver = G.ROOT-SERVERS.NET
A.ROOT-SERVERS.NET internet address = 198.41.0.4
H.ROOT-SERVERS.NET internet address = 128.63.2.53
B.ROOT-SERVERS.NET internet address = 128.9.0.107
C.ROOT-SERVERS.NET internet address = 192.33.4.12
D.ROOT-SERVERS.NET internet address = 128.8.10.90
E.ROOT-SERVERS.NET internet address = 192.203.230.10
I.ROOT-SERVERS.NET internet address = 192.36.148.17
F.ROOT-SERVERS.NET internet address = 192.5.5.241
G.ROOT-SERVERS.NET internet address = 192.112.36.4
This tells us that all ROOT-SERVERS.NET servers serves
EDU., so we can go on asking any of them. We'll continue asking
C. Now we want to know who serves the next level of the domain
name: mit.edu.:
> mit.edu.
Server: c.root-servers.net
Address: 192.33.4.12
Non-authoritative answer:
mit.edu nameserver = W20NS.mit.edu
mit.edu nameserver = BITSY.mit.edu
mit.edu nameserver = STRAWB.mit.edu
Authoritative answers can be found from:
W20NS.mit.edu internet address = 18.70.0.160
BITSY.mit.edu internet address = 18.72.0.3
STRAWB.mit.edu internet address = 18.71.0.151
steawb, w20ns and bitsy all serves mit.edu, we
select one and inquire about the name one more level up:
ai.mit.edu:
> server W20NS.mit.edu.
Host names are not case sensitive, but I use my mouse to cut and paste so it gets copied as-is from the screen.
Server: W20NS.mit.edu
Address: 18.70.0.160
> ai.mit.edu.
Server: W20NS.mit.edu
Address: 18.70.0.160
Non-authoritative answer:
ai.mit.edu nameserver = ALPHA-BITS.AI.MIT.EDU
ai.mit.edu nameserver = GRAPE-NUTS.AI.MIT.EDU
ai.mit.edu nameserver = TRIX.AI.MIT.EDU
ai.mit.edu nameserver = MUESLI.AI.MIT.EDU
ai.mit.edu nameserver = LIFE.AI.MIT.EDU
ai.mit.edu nameserver = BEET-CHEX.AI.MIT.EDU
ai.mit.edu nameserver = MINI-WHEATS.AI.MIT.EDU
ai.mit.edu nameserver = COUNT-CHOCULA.AI.MIT.EDU
ai.mit.edu nameserver = MINTAKA.LCS.MIT.EDU
Authoritative answers can be found from:
AI.MIT.EDU nameserver = ALPHA-BITS.AI.MIT.EDU
AI.MIT.EDU nameserver = GRAPE-NUTS.AI.MIT.EDU
AI.MIT.EDU nameserver = TRIX.AI.MIT.EDU
AI.MIT.EDU nameserver = MUESLI.AI.MIT.EDU
AI.MIT.EDU nameserver = LIFE.AI.MIT.EDU
AI.MIT.EDU nameserver = BEET-CHEX.AI.MIT.EDU
AI.MIT.EDU nameserver = MINI-WHEATS.AI.MIT.EDU
AI.MIT.EDU nameserver = COUNT-CHOCULA.AI.MIT.EDU
AI.MIT.EDU nameserver = MINTAKA.LCS.MIT.EDU
ALPHA-BITS.AI.MIT.EDU internet address = 128.52.32.5
GRAPE-NUTS.AI.MIT.EDU internet address = 128.52.36.4
TRIX.AI.MIT.EDU internet address = 128.52.37.6
MUESLI.AI.MIT.EDU internet address = 128.52.39.7
LIFE.AI.MIT.EDU internet address = 128.52.32.80
BEET-CHEX.AI.MIT.EDU internet address = 128.52.32.22
MINI-WHEATS.AI.MIT.EDU internet address = 128.52.54.11
COUNT-CHOCULA.AI.MIT.EDU internet address = 128.52.38.22
MINTAKA.LCS.MIT.EDU internet address = 18.26.0.36
So museli.ai.mit.edu is a nameserver for ai.mit.edu:
> server MUESLI.AI.MIT.EDU
Default Server: MUESLI.AI.MIT.EDU
Address: 128.52.39.7
Now I change query type, we've found the name server so now we're
going to ask about everything wheaties knows about
prep.ai.mit.edu.
> set q=any
> prep.ai.mit.edu.
Server: MUESLI.AI.MIT.EDU
Address: 128.52.39.7
prep.ai.mit.edu CPU = dec/decstation-5000.25 OS = unix
prep.ai.mit.edu
inet address = 18.159.0.42, protocol = tcp
ftp telnet smtp finger
prep.ai.mit.edu preference = 1, mail exchanger = gnu-life.ai.mit.edu
prep.ai.mit.edu internet address = 18.159.0.42
ai.mit.edu nameserver = beet-chex.ai.mit.edu
ai.mit.edu nameserver = alpha-bits.ai.mit.edu
ai.mit.edu nameserver = mini-wheats.ai.mit.edu
ai.mit.edu nameserver = trix.ai.mit.edu
ai.mit.edu nameserver = muesli.ai.mit.edu
ai.mit.edu nameserver = count-chocula.ai.mit.edu
ai.mit.edu nameserver = mintaka.lcs.mit.edu
ai.mit.edu nameserver = life.ai.mit.edu
gnu-life.ai.mit.edu internet address = 128.52.32.60
beet-chex.ai.mit.edu internet address = 128.52.32.22
alpha-bits.ai.mit.edu internet address = 128.52.32.5
mini-wheats.ai.mit.edu internet address = 128.52.54.11
trix.ai.mit.edu internet address = 128.52.37.6
muesli.ai.mit.edu internet address = 128.52.39.7
count-chocula.ai.mit.edu internet address = 128.52.38.22
mintaka.lcs.mit.edu internet address = 18.26.0.36
life.ai.mit.edu internet address = 128.52.32.80
So starting at . we found the successive name servers for the
each level in the domain name. If you had used your own DNS server
instead of using all those other servers, your named would of-course
cache all the information it found while digging this out for you, and
it would not have to ask again for a while.
In the tree analogue each ``.'' in the name is a branching
point. And each part between the ``.''s are the names of
individual branches in the tree.
We climb the tree by taking the name we want (prep.ai.mit.edu)
first finding the root (.) and then looking for the next branch
to climb, in this case edu. Once we have found it we climb it by
switching to the server that knows about that part of the name. Next
we look for the mit branch over the edu branch (the combined
name is mit.edu) and climb it by switching to a server that knows
about mit.edu. Again we look for the next branch, it's
ai.mit.edu and again we switch to the server that knows about it.
Now we have arrived at the right server, at the right branching point.
The last part is finding prep.ai.mit.edu, which is simple. In
computer science we usually call prep a leaf on the tree.
A much less talked about, but just as important domain is
in-addr.arpa. It too is nested like the `normal' domains.
in-addr.arpa allows us to get the hosts name when we have its
address. A important thing here is to note that ip addresses are
written in reverse order in the in-addr.arpa domain. If you have
the address of a machine: 192.128.52.43 named proceeds just like
for the prep.ai.mit.edu example: find arpa. servers. Find
in-addr.arpa. servers, find 192.in-addr.arpa. servers, find
128.192.in-addr.arpa. servers, find 52.128.192.in-addr.arpa.
servers. Find needed records for 43.52.128.192.in-addr.arpa.
Clever huh? (Say `yes'.) The reversion of the numbers can be
confusing for years though.
I have just told a lie. DNS does not work precisely the way I just told you. But it's close enough.
Now to define our own domain. We're going to make the domain
linux.bogus and define machines in it. I use a totally bogus
domain name to make sure we disturb no-one Out There.
One more thing before we start: Not all characters are allowed in
host names. We're restricted to the characters of the English
alphabet: a-z, and numbers: 0-9 and the character '-' (dash). Keep to
those characters. Upper and lower-case characters are the same for
DNS, so pat.uio.no is identical to Pat.UiO.No.
We've already started this part with this line in named.conf:
zone "0.0.127.in-addr.arpa" {
type master;
file "pz/127.0.0";
};
Please note the lack of `.' at the end of the domain names in
this file. This says that now we will define the zone
0.0.127.in-addr.arpa, that we're the master server for it and
that it is stored in a file called pz/127.0.0. We've already
set up this file, it reads:
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
1 ; Serial
8H ; Refresh
2H ; Retry
1W ; Expire
1D) ; Minimum TTL
NS ns.linux.bogus.
1 PTR localhost.
Please note the `.' at the end of all the full domain names in
this file, in contrast to the named.conf file above. Some people
like to start each zone file with a $ORIGIN directive, but
this is superfluous. The origin (where in the DNS hierarchy it
belongs) of a zone file is specified in the zone section of the
named.conf file, in this case it's 0.0.127.in-addr.arpa.
This `zone file' contains 3 `resource records' (RRs): A SOA RR. A NS RR and a PTR RR. SOA is short for Start Of Authority. The `@' is a special notation meaning the origin, and since the `domain' column for this file says 0.0.127.in-addr.arpa the first line really means
0.0.127.in-addr.arpa. IN SOA ...
NS is the Name Server RR. There is no '@' at the start of this line, it is implicit since the last line started with a '@'. Saves some typing that. So the NS line could also be written
0.0.127.in-addr.arpa. IN NS ns.linux.bogus
It tells DNS what machine is the name server of the domain
0.0.127.in-addr.arpa, it is ns.linux.bogus. 'ns' is a
customary name for name-servers, but as with web servers who are
customarily named www.something the name may be anything.
And finally the PTR record says that the host at address 1 in the
subnet 0.0.127.in-addr.arpa, i.e., 127.0.0.1 is named
localhost.
The SOA record is the preamble to all zone files, and there
should be exactly one in each zone file. It describes the zone, where
it comes from (a machine called ns.linux.bogus), who is
responsible for its contents (hostmaster@linux.bogus, you should
insert your e-mail address here), what version of the zone file this
is (serial: 1), and other things having to do with caching and
secondary DNS servers. For the rest of the fields (refresh, retry,
expire and minimum) use the numbers used in this HOWTO and you should
be safe.
Now restart your named (the command is ndc restart) and use
nslookup to examine what you've done:
$ nslookup
Default Server: localhost
Address: 127.0.0.1
> 127.0.0.1
Server: localhost
Address: 127.0.0.1
Name: localhost
Address: 127.0.0.1
so it manages to get localhost from 127.0.0.1, good. Now for our
main task, the linux.bogus domain, insert a new 'zone' section in
named.conf:
zone "linux.bogus" {
notify no;
type master;
file "pz/linux.bogus";
};
Note again the lack of ending `.' on the domain name in the
named.conf file.
In the linux.bogus zone file we'll put some totally bogus
data:
;
; Zone file for linux.bogus
;
; The full zone file
;
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199802151 ; serial, todays date + todays serial #
8H ; refresh, seconds
2H ; retry, seconds
1W ; expire, seconds
1D ) ; minimum, seconds
;
NS ns ; Inet Address of name server
MX 10 mail.linux.bogus ; Primary Mail Exchanger
MX 20 mail.friend.bogus. ; Secondary Mail Exchanger
;
localhost A 127.0.0.1
ns A 192.168.196.2
mail A 192.168.196.4
Two things must be noted about the SOA record. ns.linux.bogus
must be a actual machine with a A record. It is not legal to
have a CNAME record for he machine mentioned in the SOA record. It's
name need not be `ns', it could be any legal host name. Next,
hostmaster.linux.bogus should be read as hostmaster@linux.bogus, this
should be a mail alias, or a mailbox, where the person(s) maintaining
DNS should read mail frequently. Any mail regarding the domain will
be sent to the address listed here. The name need not be
`hostmaster', it can be your normal e-mail address, but the e-mail
address `hostmaster' is often expected to work as well.
There is one new RR type in this file, the MX, or Mail eXchanger
RR. It tells mail systems where to send mail that is addressed to
someone@linux.bogus, namely too mail.linux.bogus or
mail.friend.bogus. The number before each machine name is that
MX RRs priority. The RR with the lowest number (10) is the one mail
should be sent to if possible. If that fails the mail can be sent to
one with a higher number, a secondary mail handler, i.e.,
mail.friend.bogus which has priority 20 here.
Restart named by running ndc restart. Examine the results
with nslookup:
$ nslookup
> set q=any
> linux.bogus
Server: localhost
Address: 127.0.0.1
linux.bogus
origin = ns.linux.bogus
mail addr = hostmaster.linux.bogus
serial = 199802151
refresh = 28800 (8 hours)
retry = 7200 (2 hours)
expire = 604800 (7 days)
minimum ttl = 86400 (1 day)
linux.bogus nameserver = ns.linux.bogus
linux.bogus preference = 10, mail exchanger = mail.linux.bogus.linux.bogus
linux.bogus preference = 20, mail exchanger = mail.friend.bogus
linux.bogus nameserver = ns.linux.bogus
ns.linux.bogus internet address = 192.168.196.2
mail.linux.bogus internet address = 192.168.196.4
Upon careful examination you will discover a bug. The line
linux.bogus preference = 10, mail exchanger = mail.linux.bogus.linux.bogus
is all wrong. It should be
linux.bogus preference = 10, mail exchanger = mail.linux.bogus
I deliberately made a mistake so you could learn from it :-) Looking in the zone file we find that the line
MX 10 mail.linux.bogus ; Primary Mail Exchanger
is missing a period. Or has a 'linux.bogus' too many. If a machine
name does not end in a period in a zone file the origin is added to
its end causing the double linux.bogus.linux.bogus. So either
MX 10 mail.linux.bogus. ; Primary Mail Exchanger
or
MX 10 mail ; Primary Mail Exchanger
is correct. I prefer the latter form, it's less to type. There are
some bind experts that disagree, and some that agree with this. In a
zone file the domain should either be written out and ended with a
`.' or it should not be included at all, in which case it
defaults to the origin.
I must stress that in the named.conf file there should not be
`.'s after the domain names. You have no idea how many times a
`.' too many or few have fouled up things and confused the h*ll
out of people.
So having made my point here is the new zone file, with some extra information in it as well:
;
; Zone file for linux.bogus
;
; The full zone file
;
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199802151 ; serial, todays date + todays serial #
8H ; refresh, seconds
2H ; retry, seconds
1W ; expire, seconds
1D ) ; minimum, seconds
;
TXT "Linux.Bogus, your DNS consultants"
NS ns ; Inet Address of name server
NS ns.friend.bogus.
MX 10 mail ; Primary Mail Exchanger
MX 20 mail.friend.bogus. ; Secondary Mail Exchanger
localhost A 127.0.0.1
gw A 192.168.196.1
HINFO "Cisco" "IOS"
TXT "The router"
ns A 192.168.196.2
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "Pentium" "Linux 2.0"
www CNAME ns
donald A 192.168.196.3
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "i486" "Linux 2.0"
TXT "DEK"
mail A 192.168.196.4
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "386sx" "Linux 1.2"
ftp A 192.168.196.5
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "P6" "Linux 2.1.86"
There are a number of new RRs here: HINFO (Host INFOrmation) has two parts, it's a good habit to quote each. The first part is the hardware or CPU on the machine, and the second part the software or OS on the machine. The machine called 'ns' has a Pentium CPU and runs Linux 2.0. CNAME (Canonical NAME) is a way to give each machine several names. So www is an alias for ns.
CNAME record usage is a bit controversial. But it's safe to follow the rule that a MX, CNAME or SOA record should never refer to a CNAME record, they should only refer to something with a A record, so it is inadvisable to have
foobar CNAME www ; NO!
but correct to have
foobar CNAME ns ; Yes!
It's also safe to assume that a CNAME is not a legal host name for
a e-mail address: webmaster@www.linux.bogus is an illegal e-mail
address given the setup above. You can expect quite a few mail admins
Out There to enforce this rule even if it works for you. The way to
avoid this is to use A records (and perhaps some others too, like a MX
record) instead:
www A 192.168.196.2
A number of the arch-bind-wizards, recommend not using CNAME at all. But the discussion of why or why not is beyond this HOWTO.
But as you see, this HOWTO and many sites does not follow this rule.
Load the new database by running ndc reload, this causes named
to read its files again.
$ nslookup
Default Server: localhost
Address: 127.0.0.1
> ls -d linux.bogus
This means that all records should be listed. It results in this:
[localhost]
$ORIGIN linux.bogus.
@ 1D IN SOA ns hostmaster (
199802151 ; serial
8H ; refresh
2H ; retry
1W ; expiry
1D ) ; minimum
1D IN NS ns
1D IN NS ns.friend.bogus.
1D IN TXT "Linux.Bogus, your DNS consultants"
1D IN MX 10 mail
1D IN MX 20 mail.friend.bogus.
gw 1D IN A 192.168.196.1
1D IN HINFO "Cisco" "IOS"
1D IN TXT "The router"
mail 1D IN A 192.168.196.4
1D IN MX 10 mail
1D IN MX 20 mail.friend.bogus.
1D IN HINFO "386sx" "Linux 1.0.9"
localhost 1D IN A 127.0.0.1
www 1D IN CNAME ns
donald 1D IN A 192.168.196.3
1D IN MX 10 mail
1D IN MX 20 mail.friend.bogus.
1D IN HINFO "i486" "Linux 1.2"
1D IN TXT "DEK"
ftp 1D IN A 192.168.196.5
1D IN MX 10 mail
1D IN MX 20 mail.friend.bogus.
1D IN HINFO "P6" "Linux 1.3.59"
ns 1D IN A 192.168.196.2
1D IN MX 10 mail
1D IN MX 20 mail.friend.bogus.
1D IN HINFO "Pentium" "Linux 1.2"
That's good. As you see it looks a lot like the zone file itself.
Let's check what it says for www alone:
> set q=any
> www.linux.bogus.
Server: localhost
Address: 127.0.0.1
www.linux.bogus canonical name = ns.linux.bogus
linux.bogus nameserver = ns.linux.bogus
linux.bogus nameserver = ns.friend.bogus
ns.linux.bogus internet address = 192.168.196.2
In other words, the real name of www.linux.bogus is
ns.linux.bogus, and it gives you some of the information it has
about ns as well, enough to connect to it if you were a program.
Now we're halfway.
Now programs can convert the names in linux.bogus to addresses which they can connect to. But also required is a reverse zone, one making DNS able to convert from an address to a name. This name is used buy a lot of servers of different kinds (FTP, IRC, WWW and others) to decide if they want to talk to you or not, and if so, maybe even how much priority you should be given. For full access to all services on the Internet a reverse zone is required.
Put this in named.conf:
zone "196.168.192.in-addr.arpa" {
notify no;
type master;
file "pz/192.168.196";
};
This is exactly as with the 0.0.127.in-addr.arpa, and the
contents are similar:
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199802151 ; Serial, todays date + todays serial
8H ; Refresh
2H ; Retry
1W ; Expire
1D) ; Minimum TTL
NS ns.linux.bogus.
1 PTR gw.linux.bogus.
2 PTR ns.linux.bogus.
3 PTR donald.linux.bogus.
4 PTR mail.linux.bogus.
5 PTR ftp.linux.bogus.
Now you restart your named (ndc restart) and examine your
work with nslookup again:
> 192.168.196.4 Server: localhost Address: 127.0.0.1 Name: mail.linux.bogus Address: 192.168.196.4
so, it looks OK, dump the whole thing to examine that too:
> ls -d 196.168.192.in-addr.arpa
[localhost]
$ORIGIN 196.168.192.in-addr.arpa.
@ 1D IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199802151 ; serial
8H ; refresh
2H ; retry
1W ; expiry
1D ) ; minimum
1D IN NS ns.linux.bogus.
1 1D IN PTR gw.linux.bogus.
2 1D IN PTR ns.linux.bogus.
3 1D IN PTR donald.linux.bogus.
4 1D IN PTR mail.linux.bogus.
5 1D IN PTR ftp.linux.bogus.
@ 1D IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199802151 ; serial
8H ; refresh
2H ; retry
1W ; expiry
1D ) ; minimum
Looks good! If your output didn't look like that look for error-messages in your syslog, I explained how to do that at the very beginning of this chapter.
There are some things I should add here. The IP numbers used in
the examples above are taken from one of the blocks of 'private nets',
i.e., they are not allowed to be used publicly on the internet. So
they are safe to use in an example in a HOWTO. The second thing is
the notify no; line. It tells named not to notify its secondary
(slave) servers when it has gotten a update to one of its zone files.
In bind-8 the named can notify the other servers listed in NS records
in the zone file when a zone is updated. This is handy for ordinary
use, but for private experiments with zones this feature should be
off, we don't want the experiment to pollute the Internet do we?
And, of course, this domain is highly bogus, and so are all the addresses in it. For a real example of a real-life domain see the next main-section.
There are a couple of ``gotchas'' that normally are avoided with name lookups that are often seen when setting up reverse zones. Before you go on you need reverse lookups of your machines working on your own nameserver. If it isn't go back and fix it before continuing.
I will discuss two failures of reverse lookups as seen from outside your network:
When you ask a service provider for a network-address range and a domain name the domain name is normally delegated as a matter of course. A delegation is the glue NS record that helps you get from one nameserver to another as explained in the dry theory section above. You read that, right? If your reverse zone dosn't work go back and read it. Now.
The reverse zone also needs to be delegated. If you got the
192.168.196 net with the linux.bogus domain from your
provider they need to put NS records in for your reverse zone as
well as for your forward zone. If you follow the chain from
in-addr.arpa and up to your net you will probably find a break in
the chain. Most probably at your service provider. Having found the
break in the chain contact your service-provider and ask them to
correct the error.
This is a somewhat advanced topic, but classless subnets are very common these days and you probably have one unless you're a medium sized company.
A classless subnet is what keeps the Internet going these days. Some years ago there was much ado about the shortage of ip numbers. The smart people in IETF (the Internet Engineering Task Force, they keep the Internet working) stuck their heads together and solved the problem. At a price. The price is that you'll get less than a ``C'' subnet and some things may break. Please see Ask Mr. DNS at http://www.acmebw.com/askmrdns/00007.htm for an good explanation of this and how to handle it.
Did you read it? I'm not going to explain it so please read it.
The first part of the problem is that your ISP must understand the technique described by Mr. DNS. Not all small ISPs have a working understanding of this. If so you might have to explain to them and be persistent. But be sure you understand it first ;-). They will then set up a nice reverse zone at their server which you can examine for correctness with nslookup.
The second and last part of the problem is that you must understand the technique. If you're unsure go back and read about it again. Then you can set up your own classless reverse zone as described by Mr. DNS.
There is another trap lurking here. Old resolvers will not be
able to follow the CNAME trick in the resolving chain and will
fail to reverse-resolve your machine. This can result in the service
assigning it an incorrect access class, deny access or something along
those lines. If you stumble into such a service the only solution
(that I know of) is for your ISP to insert your PTR record directly
into their trick classless zone file instead of the trick CNAME
record.
Some ISPs will offer other ways to handle this, like Web based forms for you to input your reverse-mappings in or other automagical systems.
Where we list some real zone files
Users have suggested that I include a real example of a working domain as well as the tutorial example.
I use this example with permission from David Bullock of LAND-5. These files were current 24th of September 1996, and were then edited to fit bind 8 restrictions and use extensions by me. So, what you see here differs a bit from what you find if you query LAND-5's name servers now.
Here we find master zone sections for the two reverse zones needed:
the 127.0.0 net, as well as LAND-5's 206.6.177 subnet. And a
primary line for land-5's forward zone land-5.com. Also note that
instead of stuffing the files in a directory called pz, as I do
in this HOWTO, he puts them in a directory called zone.
// Boot file for LAND-5 name server
options {
directory "/var/named";
};
zone "." {
type hint;
file "root.hints";
};
zone "0.0.127.in-addr.arpa" {
type master;
file "zone/127.0.0";
};
zone "land-5.com" {
type master;
file "zone/land-5.com";
};
zone "177.6.206.in-addr.arpa" {
type master;
file "zone/206.6.177";
};
If you put this in your named.conf file to play with PLEASE
put ``notify no;'' in the zone sections for the two land-5
zones so as to avoid accidents.
Keep in mind that this file is dynamic, and the one listed here is old. You're better off using one produced now, with dig, as explained earlier.
; <<>> DiG 8.1 <<>> @A.ROOT-SERVERS.NET. ; (1 server found) ;; res options: init recurs defnam dnsrch ;; got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10 ;; flags: qr aa rd; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 13 ;; QUERY SECTION: ;; ., type = NS, class = IN ;; ANSWER SECTION: . 6D IN NS G.ROOT-SERVERS.NET. . 6D IN NS J.ROOT-SERVERS.NET. . 6D IN NS K.ROOT-SERVERS.NET. . 6D IN NS L.ROOT-SERVERS.NET. . 6D IN NS M.ROOT-SERVERS.NET. . 6D IN NS A.ROOT-SERVERS.NET. . 6D IN NS H.ROOT-SERVERS.NET. . 6D IN NS B.ROOT-SERVERS.NET. . 6D IN NS C.ROOT-SERVERS.NET. . 6D IN NS D.ROOT-SERVERS.NET. . 6D IN NS E.ROOT-SERVERS.NET. . 6D IN NS I.ROOT-SERVERS.NET. . 6D IN NS F.ROOT-SERVERS.NET. ;; ADDITIONAL SECTION: G.ROOT-SERVERS.NET. 5w6d16h IN A 192.112.36.4 J.ROOT-SERVERS.NET. 5w6d16h IN A 198.41.0.10 K.ROOT-SERVERS.NET. 5w6d16h IN A 193.0.14.129 L.ROOT-SERVERS.NET. 5w6d16h IN A 198.32.64.12 M.ROOT-SERVERS.NET. 5w6d16h IN A 202.12.27.33 A.ROOT-SERVERS.NET. 5w6d16h IN A 198.41.0.4 H.ROOT-SERVERS.NET. 5w6d16h IN A 128.63.2.53 B.ROOT-SERVERS.NET. 5w6d16h IN A 128.9.0.107 C.ROOT-SERVERS.NET. 5w6d16h IN A 192.33.4.12 D.ROOT-SERVERS.NET. 5w6d16h IN A 128.8.10.90 E.ROOT-SERVERS.NET. 5w6d16h IN A 192.203.230.10 I.ROOT-SERVERS.NET. 5w6d16h IN A 192.36.148.17 F.ROOT-SERVERS.NET. 5w6d16h IN A 192.5.5.241 ;; Total query time: 215 msec ;; FROM: roke.uio.no to SERVER: A.ROOT-SERVERS.NET. 198.41.0.4 ;; WHEN: Sun Feb 15 01:22:51 1998 ;; MSG SIZE sent: 17 rcvd: 436
Just the basics, the obligatory SOA record, and a record that maps
127.0.0.1 to localhost. Both are required. No more should be in
this file. It will probably never need to be updated, unless your
nameserver or hostmaster address changes.
@ IN SOA land-5.com. root.land-5.com. (
199609203 ; Serial
28800 ; Refresh
7200 ; Retry
604800 ; Expire
86400) ; Minimum TTL
NS land-5.com.
1 PTR localhost.
Here we see the mandatory SOA record, the needed NS records. We
can see that he has a secondary name server at ns2.psi.net. This
is as it should be, always have a off site secondary server as
backup. We can also see that he has a master host called land-5
which takes care of many of the different Internet services, and that
he's done it with CNAMEs (a alternative is using A records).
As you see from the SOA record, the zone file originates at
land-5.com, the contact person is
root@land-5.com. hostmaster is another oft used address for
the contact person. The serial number is in the customary yyyymmdd
format with todays serial number appended; this is probably the sixth
version of zone file on the 20th of September 1996. Remember that the
serial number must increase monotonically, here there is only
one digit for todays serial#, so after 9 edits he has to wait
until tomorrow before he can edit the file again. Consider using two
digits.
@ IN SOA land-5.com. root.land-5.com. (
199609206 ; serial, todays date + todays serial #
8H ; refresh, seconds
2H ; retry, seconds
1W ; expire, seconds
1D ) ; minimum, seconds
NS land-5.com.
NS ns2.psi.net.
MX 10 land-5.com. ; Primary Mail Exchanger
TXT "LAND-5 Corporation"
localhost A 127.0.0.1
router A 206.6.177.1
land-5.com. A 206.6.177.2
ns A 206.6.177.3
www A 207.159.141.192
ftp CNAME land-5.com.
mail CNAME land-5.com.
news CNAME land-5.com.
funn A 206.6.177.2
;
; Workstations
;
ws-177200 A 206.6.177.200
MX 10 land-5.com. ; Primary Mail Host
ws-177201 A 206.6.177.201
MX 10 land-5.com. ; Primary Mail Host
ws-177202 A 206.6.177.202
MX 10 land-5.com. ; Primary Mail Host
ws-177203 A 206.6.177.203
MX 10 land-5.com. ; Primary Mail Host
ws-177204 A 206.6.177.204
MX 10 land-5.com. ; Primary Mail Host
ws-177205 A 206.6.177.205
MX 10 land-5.com. ; Primary Mail Host
; {Many repetitive definitions deleted - SNIP}
ws-177250 A 206.6.177.250
MX 10 land-5.com. ; Primary Mail Host
ws-177251 A 206.6.177.251
MX 10 land-5.com. ; Primary Mail Host
ws-177252 A 206.6.177.252
MX 10 land-5.com. ; Primary Mail Host
ws-177253 A 206.6.177.253
MX 10 land-5.com. ; Primary Mail Host
ws-177254 A 206.6.177.254
MX 10 land-5.com. ; Primary Mail Host
If you examine land-5s nameserver you will find that the host names
are of the form ws_number. As of late bind 4 versions named
started enforcing the restrictions on what characters may be used in
host names. So that does not work with bind-8 at all, and I
substituted '-' (dash) for '_' (underline) for use in this HOWTO.
Another thing to note is that the workstations don't have individual names, but rather a prefix followed by the two last parts of the IP numbers. Using such a convention can simplify maintenance significantly, but can be a bit impersonal, and, in fact, be a source of irritation among your customers.
We also see that funn.land-5.com is an alias for
land-5.com, but using an A record, not a CNAME record. This is a
good policy as noted earlier.
I'll comment on this file below
@ IN SOA land-5.com. root.land-5.com. (
199609206 ; Serial
28800 ; Refresh
7200 ; Retry
604800 ; Expire
86400) ; Minimum TTL
NS land-5.com.
NS ns2.psi.net.
;
; Servers
;
1 PTR router.land-5.com.
2 PTR land-5.com.
2 PTR funn.land-5.com.
;
; Workstations
;
200 PTR ws-177200.land-5.com.
201 PTR ws-177201.land-5.com.
202 PTR ws-177202.land-5.com.
203 PTR ws-177203.land-5.com.
204 PTR ws-177204.land-5.com.
205 PTR ws-177205.land-5.com.
; {Many repetitive definitions deleted - SNIP}
250 PTR ws-177250.land-5.com.
251 PTR ws-177251.land-5.com.
252 PTR ws-177252.land-5.com.
253 PTR ws-177253.land-5.com.
254 PTR ws-177254.land-5.com.
The reverse zone is the bit of the setup that seems to cause the
most grief. It is used to find the host name if you have the IP
number of a machine. Example: you are an IRC server and accept
connections from IRC clients. However you are a Norwegian IRC server
and so you only want to accept connections from clients in Norway and
other Scandinavian countries. When you get a connection from a client
the C library is able to tell you the IP number of the connecting
machine because the IP number of the client is contained in all the
packets that are passed over the network. Now you can call a function
called gethostbyaddr that looks up the name of a host given the IP
number. Gethostbyaddr will ask a DNS server, which will then traverse
the DNS looking for the machine. Supposing the client connection is
from ws-177200.land-5.com. The IP number the C library provides to
the IRC server is 206.6.177.200. To find out the name of that machine
we need to find 200.177.6.206.in-addr.arpa. The DNS server will
first find the arpa. servers, then find in-addr.arpa.
servers, following the reverse trail through 206, then 6 and at last
finding the server for the 177.6.206.in-addr.arpa zone at LAND-5.
From which it will finally get the answer that for
200.177.6.206.in-addr.arpa we have a ``PTR
ws-177200.land-5.com'' record, meaning that the name that goes with
206.6.177.200 is ws-177200.land-5.com. As with the
explanation of how prep.ai.mit.edu is looked up, this is slightly
fictitious.
Getting back to the IRC server example. The IRC server only
accepts connections from the Scandinavian countries, i.e., *.no,
*.se, *.dk, the name ws-177200.land-5.com clearly does
not match any of those, and the server will deny the connection. If
there was no reverse mapping of 206.2.177.200 through the
in-addr.arpa zone the server would have been unable to find the
name at all and would have to settle to comparing 206.2.177.200
with *.no, *.se and *.dk, none of which will match.
Some people will tell you that reverse lookup mappings are only important for servers, or not important at all. Not so: Many ftp, news, IRC and even some http (WWW) servers will not accept connections from machines of which they are not able to find the name. So reverse mappings for machines are in fact mandatory.
Keeping it working.
There is one maintenance task you have to do on nameds, other than
keeping them running. That's keeping the root.hints file
updated. The easiest way is using dig, first run dig with no
arguments, you will get the root.hints according to your own
server. Then ask one of the listed root servers with dig
@rootserver. You will note that the output looks terribly like a
root.hints file. Save it to a file (dig @e.root-servers.net . ns
>root.hints.new) and replace the old root.hints with it.
Remember to reload named after replacing the cache file.
Al Longyear sent me this script, that can be run automatically to
update root.hints, install a crontab entry to run it once a month
and forget it. The script assumes you have mail working and that the
mail-alias `hostmaster' is defined. You must hack it to suit your
setup.
#!/bin/sh
#
# Update the nameserver cache information file once per month.
# This is run automatically by a cron entry.
#
# Original by Al Longyear
# Updated for bind 8 by Nicolai Langfeldt
# Miscelanious error-conditions reported by David A. Ranch
# Ping test suggested by Martin Foster
#
(
echo "To: hostmaster <hostmaster>"
echo "From: system <root>"
echo "Subject: Automatic update of the root.hints file"
echo
PATH=/sbin:/usr/sbin:/bin:/usr/bin:
export PATH
cd /var/named
# Are we online? Ping a server at your ISP
case `ping -qnc some.machine.net` in
*'100% packet loss'*)
echo "The network is DOWN. root.hints NOT updated"
echo
exit 0
;;
esac
dig @rs.internic.net . ns >root.hints.new 2>&1
case `cat root.hints.new` in
*NOERROR*)
# It worked
:;;
*)
echo "The root.hints file update has FAILED."
echo "This is the dig output reported:"
echo
cat root.hints.new
exit 0
;;
esac
echo "The root.hints file has been updated to contain the following
information:"
echo
cat root.hints.new
chown root.root root.hints.new
chmod 444 root.hints.new
rm -f root.hints.old
mv root.hints root.hints.old
mv root.hints.new root.hints
ndc restart
echo
echo "The nameserver has been restarted to ensure that the update is complete."
echo "The previous root.hints file is now called
/var/named/root.hints.old."
) 2>&1 | /usr/lib/sendmail -t
exit 0
Some of you might have picked up that the root.hints file is
also available by ftp from Internic. Please don't use ftp to update
root.hints, the above method is much more friendly to the net,
and Internic.
This was originally a section on using bind 8 written by David E. Smith (dave@bureau42.ml.org). I have edited it some to fit the new section name.
There's not much to it. Except for using named.conf instead of named.boot, everything is identical. And bind8 comes with a perl script that converts old-style files to new. Example named.boot (old style) for a cache-only name server:
directory /var/named cache . root.hints primary 0.0.127.IN-ADDR.ARPA 127.0.0.zone primary localhost localhost.zone
On the command line, in the bind8/src/bin/named directory (this assumes you got a source distribution. If you got a binary package the script is probably around, I'm not sure where it would be though. -ed.), type:
./named-bootconf.pl < named.boot > named.conf
Which creates named.conf:
// generated by named-bootconf.pl
options {
directory "/var/named";
};
zone "." {
type hint;
file "root.hints";
};
zone "0.0.127.IN-ADDR.ARPA" {
type master;
file "127.0.0.zone";
};
zone "localhost" {
type master;
file "localhost.zone";
};
It works for everything that can go into a named.boot file,
although it doesn't add all of the new enhancements and configuration
options that bind8 allows. Here's a more complete named.conf
that does the same things, but a little more efficiently.
// This is a configuration file for named (from BIND 8.1 or later).
// It would normally be installed as /etc/named.conf.
// The only change made from the `stock' named.conf (aside from this
// comment :) is that the directory line was uncommented, since I
// already had the zone files in /var/named.
options {
directory "/var/named";
datasize 20M;
};
zone "localhost" IN {
type master;
file "localhost.zone";
};
zone "0.0.127.in-addr.arpa" IN {
type master;
file "127.0.0.zone";
};
zone "." IN {
type hint;
file "root.hints";
};
In the bind 8 distributions directory bind8/src/bin/named/test you find this, and copies of the zone files, that many people can just drop in and use instantly.
The formats for zone files and root.hints files are identical,
as are the commands for updating them.
Please read this section before mailing me.
You are reading the wrong HOWTO. Please see the old version of this HOWTO, which covers bind 4, at http://www.math.uio.no/~janl/DNS/
A hint: forward only;, You will probably also need
query-source port 53;
inside the ``options'' part of the named.conf file as suggested
in the example
caching section.
Make several A records for www.busy.site and use bind 4.9.3 or later. Then bind will round-robin the answers. It will not work with earlier versions of bind.
You drop the root.hints file and just do zone files. That also means you don't have to get new hint files all the time.
If the primary/master server has address 127.0.0.1 you put a line like this in the named.conf file of your secondary:
zone "linux.bogus" {
type slave;
file "sz/linux.bogus";
masters { 127.0.0.1; };
};
You may list several alternate master servers the zone can be copied
from inside the masters list, separated by ';' (semicolon).
There are three items regarding this:
I run named on my 'Masquerading' machine here. I have
two root.hints files, one called root.hints.real which contains
the real root server names and the other called root.hints.fake
which contains...
----
; root.hints.fake
; this file contains no information
----
When I go off line I copy the root.hints.fake file to root.hints and
restart named.
When I go online I copy root.hints.real to root.hints and restart
named.
This is done from ip-down & ip-up respectively.
The first time I do a query off line on a domain name named doesn't
have details for it puts an entry like this in messages..
Jan 28 20:10:11 hazchem named[10147]: No root nameserver for class IN
which I can live with.
It certainly seems to work for me. I can use the nameserver for
local machines while off the 'net without the timeout delay for
external domain names and I while on the 'net queries for external
domains work normally
I use to run my own named on all my machines which are only
occasionally connected to the Internet by modem. The nameserver only
acts as a cache, it has no area of authority and asks back for
everything at the name servers in the root.cache file. As is usual with
Slackware, it is started before nfsd and mountd.
With one of my machines (a Libretto 30 notebook) I had the problem
that sometimes I could mount it from another system connected to my
local LAN, but most of the time it didn't work. I had the same effect
regardless of using PLIP, a PCMCIA ethernet card or PPP over a serial
interface.
After some time of guessing and experimenting I found out that
apparently named messed with the process of registration nfsd and
mountd have to carry out with the portmapper upon startup (I start
these daemons at boot time as usual). Starting named after nfsd and
mountd eliminated this problem completely.
As there are no disadvantages to expect from such a modified boot
sequence I'd advise everybody to do it that way to prevent potential
trouble.
The cache is completely stored in memory, it is not written to disk at any time. Every time you kill named the cache is lost. The cache is not controllable in any way. named manages it according to some simple rules and that is it. You cannot control the cache or the cache size in any way for any reason. If you want to you can ``fix'' this by hacking named. This is however not recommended.
No, named does not save the cache when it dies. That means that the cache must be built anew each time you kill and restart named. There is no way to make named save the cache in a file. If you want you can ``fix'' this by hacking named. This is however not recommended.
linux-rules.net. How can I get the domain I want
assigned to me?
Please contact your network service provider. They will be able to help you with this. Please note that in most parts of the world you need to pay money to get a domain.
Documentation and tools.
Real Documentation exists. Online and in print. The reading of several of these is required to make the step from small time DNS admin to a big time one. In print the standard book is DNS and BIND by C. Liu and P. Albitz from O'Reilly & Associates, Sebastopol, CA, ISBN 0-937175-82-X. I read this, it's excellent, though based on bind 4, this is not a real problem though. There is also a section in on DNS in TCP/IP Network Administration, by Craig Hunt from O'Reilly..., ISBN 0-937175-82-X. Another must for Good DNS administration (or good anything for that matter) is Zen and the Art of Motorcycle Maintenance by Robert M. Pirsig :-) Available as ISBN 0688052304 and others.
Online you will find stuff on http://www.dns.net/dnsrd/ (DNS Resources Directory), http://www.isc.org/bind.html; A FAQ, a reference manual (BOG; Bind Operations Guide) as well as papers and protocol definitions and DNS hacks (these, and most, if not all, of the RFCs mentioned below, are also contained in the bind distribution). I have not read most of these, but then I'm not a big-time DNS admin either. Arnt Gulbrandsen on the other hand has read BOG and he's ecstatic about it :-). The newsgroup comp.protocols.tcp-ip.domains is about DNS. In addition there are a number of RFCs about DNS, the most important are probably these:
A. Gulbrandsen, P. Vixie, A DNS RR for specifying the location of services (DNS SRV), October 1996
Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de Groot, E. Lear, Address Allocation for Private Internets, 02/29/1996.
D. Barr, Common DNS Operational and Configuration Errors, 02/28/1996.
B. Barr Errors in RFC 1912, this is available at http://www.cis.ohio-state.edu/~barr/rfc1912-errors.html
A. Romao, Tools for DNS debugging, 11/03/1994.
C. Farrell, M. Schulze, S. Pleitner, D. Baldoni, DNS Encoding of Geographical Location, 11/01/1994.
R. Ullmann, P. Mockapetris, L. Mamakos, C. Everhart, New DNS RR Definitions, 10/08/1990.
P. Mockapetris, Domain names - implementation and specification, 11/01/1987.
P. Mockapetris, Domain names - concepts and facilities, 11/01/1987.
M. Lottor, Domain administrators operations guide, 11/01/1987.
M. Stahl, Domain administrators guide, 11/01/1987.
C. Partridge, Mail routing and the domain system, 01/01/1986.