What the period does, at the end of a dns value

Often times, we see clients making dns changes incorrectly, generating values like one of these:

domain.com.domain.com.  A    1.2.3.4
domain.com.             NS    ns1.domain.com.domain.com.

Obviously, that doesn't look right; we don't need the domain to be repeated.

The cause of this relates to the all-important usage of the period, or "dot" at the very end of the value.

What a period does at the end of a value, is it tells named that we do not want the domain added to the end of that value.
If we leave the dot out, then name will add the domain to the end of the value.


For example, if you see the above NS record, it means you might have entered something like this:

domain.com.     NS   ns1.domain.com

where there is no trailing period at the end of the NS value.
Note how there is a period at the end of the NS name (left side).
For this case, what you actually want to see would be one of these entries:

domain.com.    NS    ns1.domain.com.
domain.com.    NS    ns1

where they're both equivalent values.
The shorter "ns1" entry is the exact same as "ns1.domain.com.", assuming the ns1 A record is in the same zone (eg: you've created your own name servers for this domain).  Because there is no period at the end of the "ns1" value, bind adds domain.com. to the end of it.

If in doubt, use the full ns1.domain.com. with the period at the end.