Default Domain question.

Barry Margolin barmar at genuity.net
Wed Sep 26 14:39:57 UTC 2001


In article <9or3uv$h09 at pub3.rc.vix.com>, Sean Knox  <Sknox at CQOS.COM> wrote:
>
>I'm sorry if this is off-topic, as this is more a general DNS question than
>a specific one about BIND.
>
>If you define a default domain on a host, say a Windows 2000 box or a
>router, when exactly is that domain appended on? i.e. if we define devel.net
>as the default domain, and I ping a working host on devel.net by host name
>only:
>
>Router#ping server
>Sending 5, 100-byte ICMP Echos to 10.10.50.125, timeout is 2 seconds:
>!!!!!
>Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
>
>obviously devel.net is appended on. 
>
>How do the nameserver resolve (or should I say attempt to) when I ping
>"server.devel" (notice no .net)... is devel.net appended to this "unknown
>host" as well? Thanks for any information helping to clear this up.

The normal algorithm is:

If the name you type doesn't contain any "." characters, first try
appending the default domain, and if that fails try it without appending
anything.  So if you ping "server", it first looks for "server.devel.net",
which succeeds.

If the name does contain a ".", first try it as give, then try appending
the default domain.  So if you ping "server.devel", it will first try
"server.devel", which will fail because there's no devel top-level domain,
then it will try "server.devel.devel.net", which I suspect doesn't exist
either.

Some ancient resolvers tried to be more "clever" than this.  If appending
the entire default domain didn't work, it would try stripping off parts of
the default domain.  So when "server.devel.devel.net" failed, it would try
appending just "net", which would result in "server.devel.net", which would
succeed.  This is a bad practice, and RFC 1535 explains why.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.


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