I am unsure what the following sentence in bold means. --
I know that FQDN means the following in
I know that DNS stands for Domain Name server. It seems that DNS is the collection of FQDN.
What does the sentence in bold mean exactly?
You're not quite right about FQDN.
com
mySite
www
mySite.com
What the sentence means is that if the settings that allow a 'partial' domain to be completed (i.e. you enter www, it figures out you mean) are screwed up, you can work around this by entering the full domain.
DNS means Domain Name System, not Domain Name server. Chaos is correct with this answer, but didn't mention this one item.
Most computers have a "domain search suffix" given to them by their DHCP server or statically configured (or by other means). Let's say you're using a computer at a college that has the domain mycollege.edu and the computer you're using has a domain search suffix of the following:
labs.mycollege.edu
mycollege.edu
This means that if you try to access the computer by name "mylaptop" that DNS will look for the following names:
mylaptop.labs.mycollege.edu
mylaptop.mycollege.edu
If the computer, however, is actually in DNS as mylaptop.chemdept.labs.mycollege.edu, then the default search lists will not help you locate the computer by providing just the short name. In that case you need to supply the FQDN (Fully Qualified Domain Name) -- the FULL name of the computer -- for a DNS lookup to succeed.
To see your domain search suffix list, on UNIX do the following:
cat /etc/resolv.conf
and look at the line that starts with "search". On Windows, in a command window, enter the following command:
ipconfig/all
and look for the part of the output listing "DNS Suffix Search List"
A fully qualified DNS name is simply a name that must not have any further stuff added to it to aid in it's resolution, or as it says in the wikipedia article "A fully qualified domain name is distinguished by its unambiguity; it can only be interpreted one way."
For instance, pn. is a fully qualified domain name.
The trailing period is important.
The trailing period tells your computer's resolver "do not add my dns domain or any of the other domains in my resolver's search list to this name I'm looking up." I did a quick check and there are several TLDs that resolve to real IP addresses, tk. being one that also is running a web server on that IP address.
Your computer is configured with an IP address it sends all DNS requests to. It is also (optionally) configured with a "domain" and a "search list", for the purposes of DNS resolution, they both behave the same way; when your computer looks up an "unqualified" name it automatically appends these (in order) to the search.
let's say your computer has a dns server of 1.2.3.4 and a domain of example.com and in the search list you also have snoopy.org. If you attempt to look up the name "woodstock" your computer will assume you really mean to look up "woodstock.example.com" and append that in the request it sends to the DNS server (1.2.3.4). If 1.2.3.4 responds with a "no such name" sort of error, your computer will then ask it to resolve "woodstock.snoopy.org" and maybe it will get an answer. If you ask your computer to look up "woodstock." then your are telling your computer "please do not append anything onto my DNS request."
A couple things that you could use some pointers on:
TCP/IP controllers can be setup to 'search' domains. You will most likley find this in organizations who have elimited their NetBios traffic and Wins servers all together and search a domain name suffixs to find hosts.
So if I automatically had my DNS settings in my TCP/IP controllers set correctly, with mysite.com as the primary suffix and configured to search that... than attepted to perform the resolution of www,
I would get two answers if the DNS server had this (A) record in its tables.
I would get the FQDN
and the IP address!
A FQDn refers to a DNS name with everything required to unambiguously resolve it. There are alot of answers about resolv.conf (I'm suprised that host files haven't gotten a mention yet) which have nothing to do with an FQDN. An FQDN does not require anything but a dns lookup to resolve the proper IP address. Any other shortcuts, suffix lists, or a hostname look staff that types the Ip in for you have no bearing on what an FQDN is.
so:
myserver - not an FQDN even if you can ping it and it resolves to myserver.mydomain.com- is an FQDN because it can be resolved all the way from the top level domain (com) down to the host name (www). Even if the server's hostname is myserver, could be set to resolve to myserver -is also an FQDN. an FQDN can (AND MUST) contain all the subdomains required to resolve from the top of the namespace to the individual host
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