CNAME to external Host record

  • Thread starter Thread starter Robert Cervantez
  • Start date Start date
R

Robert Cervantez

I'm having a problem resolving the IP address of a remote node using a CNAME
entry.

We have an FTP site that is being hosted by an 3rd party and they have named
the FTP site:
yourftp.somedomain.com
I think the IP address (hosted by the 3rd party) occassionally changes, but
I have no control over that matter.

I would like to be able to resolve the node's IP address using a name that
my users are famililar with... like:
ourftp.ourdomain.com

I have tried to create a CNAME entry on our AD-Integrated DNS servers using
the following configuration:
ourftp.ourdomain.com -> yourftp.somedomain.com

When I try to ping ourftp.ourdomain.com from the command prompt, I get the
following results:
C:\>ping ourftp.ourdomain.com
Ping request could not find host ourftp.ourdomain.com. Please check the name
and try again.

Here is the results of the nslookup resolution:
C:\>nslookup
Default Server: ourdns.ourdomain.com
Address: 10.10.1.40
set type=any
ourftp
Click to expand...
Server: ourdns.ourdomain.com
Address: 10.10.1.40

ourftp.ourdomain.com canonical name = yourftp.somedomain.com
ourftp.ourdomain.com
Click to expand...
Server: ourdns.ourdomain.com
Address: 10.10.1.40

ourftp.ourdomain.com canonical name = yourftp.somedomain.com
As you can see, the server doesn't resolve the yourftp.somedomain.com
address. Our DNS server can resolve external addresses just fine, so it's
not a connectivity issue.

What am I missing? By the way, I know it can be done because our external
DNS hosting company has successfully done it - I just need to have our
internal win2k DNS servers do it.

Thanks,
Rob.
 
Robert Cervantez said:
We have an FTP site that is being hosted by an 3rd party and they have named
the FTP site:
yourftp.somedomain.com
I think the IP address (hosted by the 3rd party) occassionally changes, but
I have no control over that matter.
Click to expand...

In your internal somedomain.com zone create a delegation named "yourftp" (if
that is the actual name if not you must use the actual name) then make that
delegation point to the Public Authoritative DNS servers. This delegation
must point to the authoritative DNS servers to work. Using a delegation
means that it won't matter if the IP changes.
 
What should happen is that the DNS server will resolve the CNAME on behalf of the client. So the client sends a request for ourftp.ourdomain.com. DNS sees
that the answer is a CNAME, so the DNS server will then go query for yourftp.somedomain.com. If this fails to resolve, then DNS only returns the CNAME. It
would appear by the results that your DNS server is unable to resolve yourftp.somedomain.com. From NSLOOKUP can you resolve
yourftp.somedomain.com?

You may also want to make sure that recursion is not turned off on your DNS server.

Thank you,
Mike Johnston
Microsoft Network Support

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