DNS Question

John Edwards isplist at adam.com.au
Wed May 7 10:19:08 CST 2003


Mike Gratton wrote:

> Hmm, that's interesting. I've always been under the impression that 
> CNAMEs usualy suck, if you try to use them for an NS or MX record, for 
> example. So I've always favoured mutltiple A records instead of CNAMEs.
>
> Apart for the high-maintenance factor when you need to change all of 
> the A recods pointing to an address, when else can doing this suck?

CNAME's also require 2 DNS lookups rather than one to resolve, which can 
be a noticeable difference on laggy links or busy DNS servers if you 
obsess over speed. Also, you technically shouldn't CNAME a CNAME, so 
using an alias may prevent someone else from aliasing your site (which 
might be a good thing in some scenarios, but possibly not if you're 
using dynamic DNS).

You also can't use a CNAME for the @ record in a domain which is 
annoying if you want all domains to point to a single web server for 
example, and I think that you can't use multiple CNAME's for round-robin 
DNS.

I too am curious about scenarios where multiple A records suck, I tend 
to limit my use of CNAME's to aliasing hostnames that might change IP 
without me knowing about it.

John Edwards


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