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Thursday, August 14, 2008

Custom Domain DNS Addresses And Destination Addressing Conventions

When you setup a Google Custom Domain for your blog, the essential first step is to setup one or more Address referrals. An Address referral will be entered as either an "A" ("Host") or "CNAME" ("Alias") record, and will consist of 2 essential components.
  1. A "from" address.
  2. A "to" address.
How you enter the "from" and "to" records is an essential issue - and is not universal in nature. Please note that the terms "from" and "to" are not well defined. If you find this confusing, my apologies.

Note that in this article, as throughout my blog, I'll show extracted Dig logs to describe any Address referral.

When I setup my custom domain, "nitecruzr.net", on GoDaddy, I'll use the the GoDaddy Domain Manager. Your DNS host may, or may not, be GoDaddy, and your setup may, or may not, be the same as I describe.

When I setup a "CNAME" referral, I might define a local host "blogging" ("from"), as referred to a distant host "ghs.google.com" ("to"). I'll define host "blogging.nitecruzr.net" by entering "blogging", and the DNS Manager will add the ".nitecruzr.net" for me. We then say that the "from" address is relative to the domain, or is a "relative" address.
blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com.


When I setup an "A" referral, I might define a local host "@" (aka the domain root) ("from"), as referred to a distant host ("to"), using an IP address. If I define the "to" address as "64.233.179.121", this is an "absolute" address - an IP address cannot be relative to a host name. An IP address has to be absolute.
nitecruzr.net. 3600 IN A 64.233.179.121


When I setup a "CNAME" referral, I refer the "to" addresses by host name. I'll enter the "to" address as "ghs.google.com", and the Domain Manager will add a trailing ".", giving my "CNAME" referral an absolute address.
blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com.

Do you see the trailing "."?


GoDaddy adds the trailing ".", in most cases!



That's better!!


Not all DNS Hosts work this way!

With some DNS Hosts, if I enter a "to" address as "ghs.google.com", this will be taken as a relative address. The Domain Manager may then add the domain name on the end.
blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com.nitecruzr.net.


Obviously, I do not mean to define a "to" address as "ghs.google.com.nitecruzr.net". When I setup a "CNAME" referral for these DNS hosts, I then enter the "to" address name as "ghs.google.com.", signifying an absolute address. The DNS Manager then does not add a trailing ".nitecruzr.net", and all's well.

However, I do have to know whether the Domain Manager configures "CNAME" referrals, by default, with absolute, or relative, addresses for the "to" addresses. Knowing this, I can correctly enter a "to" address with, or without, a trailing ".".

Some registrars have large server farms - and lack consistency.

Occasionally, we may encounter registrars where most servers may expect "absolute" addresses - and a few may expect "relative" addresses. Alternately, most servers may expect "relative" addresses - and a few may expect "absolute" addresses.

Such a tiny detail - and so essential. You may need to consult with Customer Support, from time to time.

Dude, hit me with a comment!