Murat
Yildirimoglu
MCSE,MCT
murat@muratyildirimoglu
When we look at
the DNS tab of the TCP/IP properties on an NT machine, we see a strange section
titled, Domain Suffix Search Order.
What is it?
What is it used for?
In the TCP/IP
configuration of an NT computer, we see a fully qualified domain name (FQDN),
for example, st9.acme.com. Let the DNS server IP address be 131.107.2.10, as
indicated in the DNS Service Search Order section. That means, when it tries to
resolve the FQDNs to their corresponding IP addresses, it goes to that DNS
Server.
DNS queries
requires FQDNs. When a command like
ping
www.winntmag.com
is
executed, the first thing to do is to
resolve the FQDN, www.winntmag.com in this case, to the corresponding IP
address.
Now, lets
assume that the DNS server has two zones, acme.com and teledyne.com. Remember
that the domain of the client is also acme.com.
Let Acme.com
has two host entries for mailserver.acme.com and ftpserver.acme.com and the
other domain has only one host entry, mainserver.
Now, lets have
some examples. First, the client will
ping mailserver.acme.com.
The user
executes a regular command. That is, it gives the FQDN of the target computer.
And the computer goes to the DNS server and can obtain an IP address against a
FQDN.
What if the
client tries to ping the ftpserver but forgets to add the domain info?
It can still
resolve the name to the IP address. How is it possible?
Because, when the
client passes not the FQDN but only the host name, TCP/IP stack on NT adds the
client's domain info to the DNS request. In our case, domain of the client,
acme.com, is added to the request and DNS query was successfully completed.
Now, if the client tries to ping the
mainserver.teledyne.com but again it forgets to add domain info to the name
what will happen?
The result of
the command will be negative.
If the client
gives the FQDN, that is mainserver.teledyne.com, the query will be succesfull.
How can I get a
positive response in this case also?
Domain suffix search order comes to the stage at this point. If we add the teledyne.com to the Domain Suffix Search Order box, TCP/IP stack tries first mainserver.acme.com. There is no computer like that. When it receives negative response it tries mainserver.teledyne.com
The domain
names in the Domain Suffix Search Order box are added to the queried computer
names, if those names do not conform to the FQDN format.