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7. A real domain example
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.
7.1 /etc/named.conf (or /var/named/named.conf)
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";
};
controls {
inet 127.0.0.1 allow { localhost; } keys { rndc_key; };
};
key "rndc_key" {
algorithm hmac-md5;
secret "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
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.
7.2 /var/named/root.hints
Keep in mind that this file is dynamic, and the one listed here is old. You're better off using a new one 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
7.3 /var/named/zone/127.0.0
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.
$TTL 3D
@ 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.
If you look at a random BIND installation you will probably find
that the $TTL line is missing as it is here. It was not used
before, and only version 8.2 of BIND has started to warn about its
absence. BIND 9 requires the $TTL.
7.4 /var/named/zone/land-5.com
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.
$TTL 3D
@ IN SOA land-5.com. root.land-5.com. (
199609206 ; serial, todays date + todays serial #
8H ; refresh, seconds
2H ; retry, seconds
4W ; 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.
But, as mentioned earlier, BIND 9 no longer enforces this restriction.
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.
7.5 /var/named/zone/206.6.177
I'll comment on this file below
$TTL 3D
@ 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 FTP server and accept
connections from FTP clients. As you are a Norwegian FTP server you
want to accept more connections from clients in Norway and other
Scandinavian countries and less from the rest of the world. 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 FTP 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.
The FTP server prioritizes 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 put the connection in a connection class with less
bandwidth and fewer clients allowed. 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 at all, it may even deny the
connection for lack of classification.
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.
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