Wildcard Q/A
Chris Buxton
cbuxton at menandmice.com
Wed Mar 21 17:54:00 UTC 2007
A wildcard is a special node in the namespace tree that is used as a
template to answer queries about its nonexistent siblings. (It also
covers descendants of non-existent siblings.) Any query for such a
nonexistent node is answered based on the template provided by the
wildcard node.
You should not have a wildcard on the right side of a CNAME record.
Instead, point the CNAME record to a normal name; that name might be
a nonexistent name that is covered by the other wildcard. What you
have may work with some resolving name servers, but I don't think it
is correct according to the RFCs.
Example:
*.foo.example. CNAME www.bar.example.
*.bar.example. A 192.0.2.1
Otherwise, there's nothing wrong with using wildcards they way you
currently do. Just be aware that, for example, if you create an MX
record with a particular name, the wildcard won't be used to
synthesize an A record for that same name in response to a query,
because that node will then exist - even though it doesn't own an A
record.
Example:
*.bar.example. A 192.0.2.1
sub.bar.example. MX 10 mail.bar.example.
Query: sub.bar.example. IN A
Answer: "no data" negative response (the node exists but does not own
that record type)
Hope this helps.
Chris Buxton
Men & Mice
On Mar 21, 2007, at 6:33 AM, AF wrote:
> I have a wildcard A record setup and pointed to my web server.. for
> example:
>
> *.bar.com. IN A 1.1.1.1
>
> The web site on this server responds to any request and builds the
> pages based on their URL (foo.bar.com, me.bar.com, etc.)
>
> I can also setup CNAMEs to do the same.. for example:
> *.foo.com. IN CNAME *.bar.com.
>
> This gives different pages & URLs too (abc.foo.com, def.foo.com, etc.)
>
> Is there a preferred way to manage that first wildcard? Why should I
> *not* do this? I have read mixed reviews about its use. Really, could
> I just have a regular A record (www.bar.com. IN A 1.1.1.1) and then
> have the wildcard CNAME pointed to it? Same end result?
>
> Thanks All.
>
>
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