Re: [dnsext] we need help to make names the same, was draft-yao-dnsext-identical-resolution-02 comment

[Tony Finch <[e-mail]>]

On Wed, 16 Feb 2011, John Levine wrote:
>
> It would not be absurd to argue that the most reasonable way to solve
> the provisioning issues is for the SMTP and HTTP servers to ask the
> DNS what the canonical name for an otherwise unknown name is, so those
> servers are just provisioned with the canonical name and an "allow
> variants" flag.

It used to be the case that SMTP servers would rewrite domains in
addresses by replacing a CNAME owner with its target. See RFC 1123 section
5.2.2. This requirement no longer exists but there is still code out there
that supports it. I think it would be quite reasonable to add a feature
for optional cname-based canonicalization to an MTA. (You can probably do
it now using Exim's configuration language, though it'll probably be a bit
ugly.)

There is also some HTTP server code out there that hooks into the DNS for
server name canonicalization - see Apache's UseCanonicalName DNS option,
which is my fault. It uses reverse DNS lookups (it was designed for
IP-based virtual hosting) but I don't think it would be hard to do
something similar based on CNAME records.

Note that server features like this are nice to have but not absolutely
necessary.

Tony.
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