Simple DNS Plus News
09 Jul 2010 - Simple DNS Plus v. 5.2 build 117 released / Problem resolving WebMD.com
Simple DNS Plus v. 5.2 build 117 is now available at http://www.simpledns.com/download.aspx
For more details on the updates and changes in this build, please see release notes.
Over the last few days, several users have reported not being able to resolve www.webmd.com.
The problem is an erroneous response (details below) from the DNS servers hosting the domain name.
We have contacted WebMD.com and their DNS provider (UltraDNS) about this and anticipate that they will fix the problem shortly.
However since WebMD.com is a very popular web-site (and UltraDNS is one of the larger DNS providers), we felt it was best to provide a quick workaround with above update to Simple DNS Plus.
When we do a lookup for www.webmd.com against one of the authoritative DNS servers (for example "pdns1.ultradns.net"), we get a response with a CNAME-record (alias) pointing to www.phx1.webmd.com and a SOA-record in the authority section:
The standard (RFC) interpretation of this SOA-record is that no records exist for the current name (www.phx1.webmd.com) and the requested record type (A) - a so called "NO DATA" response.
Therefore previous builds of Simple DNS Plus naturally stopped the resolving process here - no need to do anything more since we know the final answer (no data).
However if we do another DNS lookup for www.phx1.webmd.com against the same DNS server, we get a surprising response - now all of a sudden there IS an A-record for this name:
This is an error in the configuration or operation of the DNS servers hosting www.webmd.com, and we obviously recommend that they get this fixed as quickly as possible.
In this new build of Simple DNS Plus, we have made an exception for this very specific situation:
For responses received containing a CNAME-record in the Answer section, a "NODATA" SOA-record in Authority section is now ignored, and the CNAME alias is attempted resolved in a new outbound request.
This immediately makes it possible for Simple DNS Plus to resolve www.webmd.com and any other domain with the same problem.
The trade off is that this will also cause a few more outbound requests in certain situations. These extra requests would normally not be necessary, but it does make Simple DNS Plus more resilient against this type of problem.
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