How to set up your own domain.
Before we really start this section I'm going to serve you
some theory on how DNS works. And you're going to read it because
it's good for you. If you don't `wanna' you should at least skim it
very quickly. Stop skimming when you get to what should go in your
named.boot file.
DNS is a hierarchical 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.
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.cache 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 the server we're asking that edu is right under . (this narrows the search somewhat).
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 *.root-servers.net serves edu., so we
can go on 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 = STRAWB.mit.edu
mit.edu nameserver = W20NS.mit.edu
mit.edu nameserver = BITSY.mit.edu
Authoritative answers can be found from:
STRAWB.mit.edu internet address = 18.71.0.151
W20NS.mit.edu internet address = 18.70.0.160
BITSY.mit.edu internet address = 18.72.0.3
steawb, w20ns and bitsy serves mit, select one and
inquire about 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 = WHEATIES.AI.MIT.EDU
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
Authoritative answers can be found from:
AI.MIT.EDU nameserver = WHEATIES.AI.MIT.EDU
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
WHEATIES.AI.MIT.EDU internet address = 128.52.32.13
WHEATIES.AI.MIT.EDU internet address = 128.52.35.13
ALPHA-BITS.AI.MIT.EDU internet address = 128.52.32.5
ALPHA-BITS.AI.MIT.EDU internet address = 128.52.37.5
GRAPE-NUTS.AI.MIT.EDU internet address = 128.52.32.4
GRAPE-NUTS.AI.MIT.EDU internet address = 128.52.36.4
TRIX.AI.MIT.EDU internet address = 128.52.32.6
TRIX.AI.MIT.EDU internet address = 128.52.38.6
MUESLI.AI.MIT.EDU internet address = 128.52.32.7
MUESLI.AI.MIT.EDU internet address = 128.52.39.7
So weaties.ai.mit.edu is a nameserver for ai.mit.edu:
> server WHEATIES.AI.MIT.EDU.
Default Server: WHEATIES.AI.MIT.EDU
Addresses: 128.52.32.13, 128.52.35.13
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: WHEATIES.AI.MIT.EDU
Addresses: 128.52.32.13, 128.52.35.13
prep.ai.mit.edu CPU = dec/decstation-5000.25 OS = unix
prep.ai.mit.edu
inet address = 18.159.0.42, protocol = tcp
#21 #23 #25 #79
prep.ai.mit.edu preference = 1, mail exchanger = life.ai.mit.edu
prep.ai.mit.edu internet address = 18.159.0.42
ai.mit.edu nameserver = alpha-bits.ai.mit.edu
ai.mit.edu nameserver = wheaties.ai.mit.edu
ai.mit.edu nameserver = grape-nuts.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 = life.ai.mit.edu
ai.mit.edu nameserver = mintaka.lcs.mit.edu
life.ai.mit.edu internet address = 128.52.32.80
alpha-bits.ai.mit.edu internet address = 128.52.32.5
wheaties.ai.mit.edu internet address = 128.52.35.13
wheaties.ai.mit.edu internet address = 128.52.32.13
grape-nuts.ai.mit.edu internet address = 128.52.36.4
grape-nuts.ai.mit.edu internet address = 128.52.32.4
mini-wheats.ai.mit.edu internet address = 128.52.32.11
mini-wheats.ai.mit.edu internet address = 128.52.54.11
mintaka.lcs.mit.edu internet address = 18.26.0.36
So starting at . we found the successive name servers for the
next 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.
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 it's
address. A important thing here is to note that ip#s 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 the first 2 years.
I have just told a lie. DNS does not work literally 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.
We've already started this part with this line in named.boot:
primary 0.0.127.in-addr.arpa pz/127.0.0
Please note the lack of `.' at the end of the domain names in
this file. The first line names the file pz/127.0.0 as
defining 0.0.127.in-addr.arpa. We've already set up this file,
it reads:
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
1 ; Serial
28800 ; Refresh
7200 ; Retry
604800 ; Expire
86400) ; 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.boot 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 `domain' column of the named.boot
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, it tells DNS what machine is the name
server of the domain 0.0.127.in-addr.arpa, it is
ns.linux.bogus. And finally the PTR record says that 1 (equals
1.0.0.127.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, the very first record. It
describes the zone, where it comes from (a machine called
linux.bogus), who is responsible for its contents
(hostmaster@linux.bogus), 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 primary line in
named.boot:
primary linux.bogus pz/linux.bogus
Note the continued lack of ending `.' on the domain name in the
named.boot file.
In the linux.bogus zone file we'll put some totally bogus data:
;
; Zone file for linux.bogus
;
; Mandatory minimum for a working domain
;
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199511301 ; serial, todays date + todays serial #
28800 ; refresh, seconds
7200 ; retry, seconds
3600000 ; expire, seconds
86400 ) ; minimum, seconds
NS ns.linux.bogus.
NS ns.friend.bogus.
MX 10 mail.linux.bogus ; Primary Mail Exchanger
MX 20 mail.friend.bogus. ; Secondary Mail Exchanger
localhost A 127.0.0.1
ns A 127.0.0.2
mail A 127.0.0.4
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 any legal e-mail address, but the e-mail address `hostmaster' is 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 primarily. If that fails it 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 = linux.bogus
mail addr = hostmaster.linux.bogus
serial = 199511301
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 nameserver = ns.friend.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
linux.bogus nameserver = ns.friend.bogus
ns.linux.bogus internet address = 127.0.0.2
mail.linux.bogus internet address = 127.0.0.4
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 it's end. 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. 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. Others have strong opinions going in the other direction.
I must stress that in the named.boot 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
;
; Mandatory minimum for a working domain
;
@ IN SOA ns.linux.bogus. hostmaster.linux.bogus. (
199511301 ; serial, todays date + todays serial #
28800 ; refresh, seconds
7200 ; retry, seconds
604800 ; expire, seconds
86400 ) ; minimum, seconds
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
ns A 127.0.0.2
mail A 127.0.0.4
;
; Extras
;
@ TXT "Linux.Bogus, your DNS consultants"
ns MX 10 mail
MX 20 mail.friend.bogus.
HINFO "Pentium" "Linux 1.2"
TXT "RMS"
richard CNAME ns
www CNAME ns
donald A 127.0.0.3
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "i486" "Linux 1.2"
TXT "DEK"
mail MX 10 mail
MX 20 mail.friend.bogus.
HINFO "386sx" "Linux 1.0.9"
ftp A 127.0.0.5
MX 10 mail
MX 20 mail.friend.bogus.
HINFO "P6" "Linux 1.3.59"
You might want to move the first three A records so that they're placed next to their respective other records, instead on top like that.
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. ns has a Pentium CPU and runs Linux 1.2. The TXT record is a free text record that you can use for anything you like. CNAME (Canonical NAME) is a way to give each machine several names. So richard and www is a alias for ns. It's important to note that A MX, CNAME and SOA record should never refer to a CNAME record, they should only refer to something with a A record, so it would wrong to have
foobar CNAME richard ; NO!
but correct to have
foobar CNAME ns ; Yes!
It's also important to note 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 127.0.0.2
Paul Vixie, the primary named wizard, recommends not using CNAME. So consider not using it very seriously.
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.
[localhost]
linux.bogus. SOA ns.linux.bogus hostmaster.linux.bogus. (199511301 28800 7200 604800 86400)
linux.bogus. NS ns.linux.bogus
linux.bogus. NS ns.friend.bogus
linux.bogus. MX 10 mail.linux.bogus
linux.bogus. MX 20 mail.friend.bogus
linux.bogus. TXT "Linux.Bogus, your DNS consultants"
localhost A 127.0.0.1
mail A 127.0.0.4
mail MX 10 mail.linux.bogus
mail MX 20 mail.friend.bogus
mail HINFO 386sx Linux 1.0.9
donald A 127.0.0.3
donald MX 10 mail.linux.bogus
donald MX 20 mail.friend.bogus
donald HINFO i486 Linux 1.2
donald TXT "DEK"
www CNAME ns.linux.bogus
richard CNAME ns.linux.bogus
ftp A 127.0.0.5
ftp MX 10 mail.linux.bogus
ftp MX 20 mail.friend.bogus
ftp HINFO P6 Linux 1.3.59
ns A 127.0.0.2
ns MX 10 mail.linux.bogus
ns MX 20 mail.friend.bogus
ns HINFO Pentium Linux 1.2
ns TXT "RMS"
linux.bogus. SOA ns.linux.bogus hostmaster.linux.bogus. (199511301 28800 7200 604800 86400)
That's good. 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
...In other words, the real name of www.linux.bogus is
ns.linux.bogus
linux.bogus nameserver = ns.linux.bogus
linux.bogus nameserver = ns.friend.bogus
ns.linux.bogus internet address = 127.0.0.2
and ns.linux.bogus has the address 127.0.0.2. Looks good too.
Of course, this domain is highly bogus, and so are all the addresses in it, and it is perhaps, unfortunately a bit confusing. For a real example of a real domain see the next section.