; Virtual Winery Ethernet
vlager-if2 IN A 172.16.2.1
vbardolino IN A 172.16.2.2
vchianti IN A 172.16.2.3
vbeaujolais IN A 172.16.2.4
;
; Virtual Spirits (subsidiary) Ethernet
vbourbon IN A 172.16.3.1
vbourbon-if1 IN CNAME vbourbon
Example 6.12: The named.local File
;
; /var/named/named.local Reverse mapping of 127.0.0
; Origin is 0.0.127.in-addr.arpa.
;
@ IN SOA vlager.vbrew.com. joe.vbrew.com. (
1; serial
360000; refresh: 100 hrs
3600; retry: one hour
3600000; expire: 42 days
360000; minimum: 100 hrs
)
IN NS vlager.vbrew.com.
1 IN PTR localhost.
Example 6.13: The named.rev File
;
; /var/named/named.rev Reverse mapping of our IP addresses
; Origin is 16.172.in-addr.arpa.
;
@ IN SOA vlager.vbrew.com. joe.vbrew.com. (
16; serial
86400; refresh: once per day
3600; retry: one hour
3600000; expire: 42 days
604800; minimum: 1 week
)
IN NS vlager.vbrew.com.
; brewery
1.1 IN PTR vlager.vbrew.com.
2.1 IN PTR vstout.vbrew.com.
3.1 IN PTR vale.vbrew.com.
; winery
1.2 IN PTR vlager-if2.vbrew.com.
2.2 IN PTR vbardolino.vbrew.com.
3.2 IN PTR vchianti.vbrew.com.
4.2 IN PTR vbeaujolais.vbrew.com.
Verifying the Name Server Setup
nslookup is a great tool for checking the operation of your name server setup. It can be used both interactively with prompts and as a single command with immediate output. In the latter case, you simply invoke it as:
$ nslookup
hostname
nslookup queries the name server specified in resolv.conf for hostname. (If this file names more than one server, nslookup chooses one at random.)
The interactive mode, however, is much more exciting. Besides looking up individual hosts, you may query for any type of DNS record and transfer the entire zone information for a domain.
When invoked without an argument, nslookup displays the name server it uses and enters interactive mode. At the › prompt, you may type any domain name you want to query. By default, it asks for class A records, those containing the IP address relating to the domain name.
You can look for record types by issuing:
› set type=type
in which type is one of the resource record names described earlier, or ANY.
You might have the following nslookup session:
$ nslookup
Default Server: tao.linux.org.au
Address: 203.41.101.121
› metalab.unc.edu
Server: tao.linux.org.au
Address: 203.41.101.121
Name: metalab.unc.edu Address: 152.2.254.81
›
The output first displays the DNS server being queried, and then the result of the query.
If you try to query for a name that has no IP address associated with it, but other records were found in the DNS database, nslookup returns with an error message saying " No type A records found." However, you can make it query for records other than type A by issuing the set type command. To get the SOA record of unc.edu, you would issue:
› unc.edu
Server: tao.linux.org.au
Address: 203.41.101.121
*** No address (A) records available for unc.edu
› set type=SOA
› unc.edu
Server: tao.linux.org.au
Address: 203.41.101.121
unc.edu
origin = ns.unc.edu
mail addr = host-reg.ns.unc.edu
serial = 1998111011
refresh = 14400 (4H)
retry = 3600 (1H)
expire = 1209600 (2W)
minimum ttl = 86400 (1D)
unc.edu name server = ns2.unc.edu
unc.edu name server = ncnoc.ncren.net
unc.edu name server = ns.unc.edu
ns2.unc.edu internet address = 152.2.253.100
ncnoc.ncren.net internet address = 192.101.21.1
ncnoc.ncren.net internet address = 128.109.193.1
ns.unc.edu internet address = 152.2.21.1
In a similar fashion, you can query for MX records:
› set type=MX
› unc.edu
Server: tao.linux.org.au
Address: 203.41.101.121
unc.edu preference = 0, mail exchanger = conga.oit.unc.edu
unc.edu preference = 10, mail exchanger = imsety.oit.unc.edu
unc.edu name server = ns.unc.edu
unc.edu name server = ns2.unc.edu
unc.edu name server = ncnoc.ncren.net
conga.oit.unc.edu internet address = 152.2.22.21
imsety.oit.unc.edu internet address = 152.2.21.99
ns.unc.edu internet address = 152.2.21.1
ns2.unc.edu internet address = 152.2.253.100
ncnoc.ncren.net internet address = 192.101.21.1
ncnoc.ncren.net internet address = 128.109.193.1
Using a type of ANY returns all resource records associated with a given name.
A practical application of nslookup, besides debugging, is to obtain the current list of root name servers. You can obtain this list by querying for all NS records associated with the root domain:
› set type=NS
› .
Server: tao.linux.org.au
Address: 203.41.101.121
Non-authoritative answer:
(root) name server = A.ROOT-SERVERS.NET
(root) name server = H.ROOT-SERVERS.NET
(root) name server = B.ROOT-SERVERS.NET
(root) name server = C.ROOT-SERVERS.NET
(root) name server = D.ROOT-SERVERS.NET
(root) name server = E.ROOT-SERVERS.NET
(root) name server = I.ROOT-SERVERS.NET
(root) name server = F.ROOT-SERVERS.NET
(root) name server = G.ROOT-SERVERS.NET
(root) name server = J.ROOT-SERVERS.NET
(root) name server = K.ROOT-SERVERS.NET