--On 2000-01-06 08.59 -0600, Brian E Carpenter <brian@hursley.ibm.com>
wrote:
> It was pointed out by Erik Nordmark that SRV doesn't allow arbitrary
> wild cards:
>
>> I think there is one "bug": In section 3.6 you are saying that
>> SRV records can achieve a diversion mechanism similar to MX records.
>> I don't think that is the case since it would require non-terminal
>> wildcards as in
>> _ftp._tcp.*.example.com
>> to do a diversion akin to MX records - such things are not allowed in
>> the DNS.
The MX wildcard doesn't work the way people think. It only matches if there
is no other record with the same name, for example an A record or CNAME. It
is also the case that the wildcard only works when the wildcard itself is
the first label in the name, and not third like the example above for what
one wants in SRVs.
For operations with DNS in Sweden, I have only seen one place where MX
wildcards really work, and that is when you have a domain which is not at
all connected to the Internet, and mail is going for that domain (and
sub-domains) via UUCP or such non-internet protocols. THEN one can create
the wildcard MX. In all other cases, you can get so confused by the
matching rules between wildcard in MX and other RR types that I always
recommend people to if nothing else generate the resource records they need.
I.e. what one wants (normally) is to have all mail to all subdomains to a
parent domain go to the same host. You don't want arbitrary tokens (also
non-existing subdomains) to go to the mail host, because the error to the
sender of the email might be confusing, and not reflect the existence of
the subdomain or not.
So, yes, wildcards are somewhat useful, but MX wildcards doesn't work well,
and no, we don't have wildcards for SRV records, BUT one can quite easilly
generate all RR one need in the scripts one have anyways(?) to keep the
zones together. I.e. this doesn't need to be a function of DNS, but the
tool one uses to keep the zone up to date.
paf
This archive was generated by hypermail 2b29 : Thu Nov 18 2004 - 11:21:27 MST