[Gllug] DNS CNAME usage.

[Stephen Harker]

David Damerell wrote:
> On Friday, 17 Mar 2006, Steve Nelson wrote:
>> On 3/17/06, Stephen Harker <steve at pauken.co.uk> wrote:
>>> Does anyone have an opinion about CNAME usage and using a CNAME record
>>> to refer to a canonical name that is not part of the current domain and
>>> whether there should be problems associated with this?
>> In BIND, CNAME records can be nested up to 8 deep.  By this I mean
>> that you can have a CNAME pointing to another CNAME etc etc, but the
>> eighth must be the A record.
> 
> However CNAME chains are explicitly prohibited and not what Mr Harker
> is trying to do.

Correct. And all the documentation I've read has pretty much forbidden 
having CNAMEs pointing to CNAMEs at all, let alone 8 deep! I think BIND 
supports it but that's not a reason to do it. The rule is that you can't 
have point a record at a CNAME. So NS, MX, CNAME etc must point to 
Canonical Names and never aliases.

> Perhaps name resolution in the target domain is flaky and the CNAME is
> something of a red herring.

I think this more likely. I just rang one of the afflicted customers and 
faffed about giving him alternative A records to use and it all just 
started working "as if by magic". Certainly nothing we've changed in our 
DNS. I think "negative caching", as mentioned elsewhere, is probably to 
blame :/

Stephen
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