Diagnosing Problems With Custom Domains: Dig

Whenever I answer a problem report in an open forum, in my email, or just in general life, which involves a blog published to a Google Custom Domain, I always start my research with a Dig log.

Dig is a very commonly used tool for querying DNS configuration data. Since many custom domain problems involve DNS setup, Dig is my first diagnostic tool.

Dig can be run locally (from your computer), or online (from a Dig server). Since Dig accesses online data, I find it reasonable to run it from online servers. For detailed analysis, I use the Kloth.Net Dig utility, which lets you select specific record types to dig for, and lets you specify a DNS server to Dig into.

AN alternate Dig tool, which is useful for DNS address documentation and packaged advice, is DigWebInterface.

If the Kloth service doesn't fill your needs, you can try Dig Web Interface, which I show in my later post, Blogger Magic - Reading A Dig Log.

Let's Dig the DNS records for this domain, using Kloth. Let's first look at the primary domain "nitecruzr.net".

; <<>> DiG 9.3.2 <<>> @localhost nitecruzr.net A
; (2 servers found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55301
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;nitecruzr.net.   IN A

;; ANSWER SECTION:
 nitecruzr.net.  3600 IN A 64.233.179.121
nitecruzr.net.  3600 IN A 66.249.81.121
nitecruzr.net.  3600 IN A 72.14.207.121

;; Query time: 160 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Oct 24 23:43:30 2008
;; MSG SIZE  rcvd: 79

Next, the "www" alias "www.nitecruzr.net".

; <<>> DiG 9.3.2 <<>> @localhost www.nitecruzr.net A
; (2 servers found)
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12647
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.nitecruzr.net.  IN A

;; ANSWER SECTION:
www.nitecruzr.net. 3600 IN CNAME ghs.google.com.
ghs.google.com.  34422 IN CNAME ghs.l.google.com.
ghs.l.google.com. 300 IN A 72.14.207.121

;; Query time: 175 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Oct 24 23:43:42 2008
;; MSG SIZE  rcvd: 99

Now please note that the above logs are enormously wasteful in space. When I present Dig data in an online forum, I'll typically excerpt it to just the essential data.

 nitecruzr.net.  3600 IN A 64.233.179.121
nitecruzr.net.  3600 IN A 66.249.81.121
nitecruzr.net.  3600 IN A 72.14.207.121
www.nitecruzr.net. 3600 IN CNAME ghs.google.com.
---
ghs.google.com.  34422 IN CNAME ghs.l.google.com.
ghs.l.google.com. 300 IN A 72.14.207.121

In some of my articles, I'll abridge the log, showing the context of the query.

;; QUESTION SECTION:
;nitecruzr.net.   IN A
;; ANSWER SECTION:
 nitecruzr.net.  3600 IN A 64.233.179.121
nitecruzr.net.  3600 IN A 66.249.81.121
nitecruzr.net.  3600 IN A 72.14.207.121
;; QUESTION SECTION:
;www.nitecruzr.net.  IN A
;; ANSWER SECTION:
www.nitecruzr.net. 3600 IN CNAME ghs.google.com.
ghs.google.com.  34422 IN CNAME ghs.l.google.com.
ghs.l.google.com. 300 IN A 72.14.207.121

What do we see in the above examples (abridged or condensed)?

• The primary domain (ie, the "domain root") is redirected by Address ("A") to 3 servers, provided by Google Apps, "64.233.179.121", "66.249.81.121", and "72.14.207.121". Please note that, as of 2008/10/24, this configuration became out of date, and was replaced by 4 mutually redundant servers.
• The "www" alias is redirected by Alias ("CNAME") to the Google custom domain load balancing DNS proxy, "ghs.google.com".
• Each Address and Alias has a Time To Live ("TTL") of 3600 seconds, ie 1 hour. That one hour is the amount of time that a local DNS server can consider the DNS entry in its cache to be fresh.
  
  If a non authoritative server is asked for DNS information, it checks its cache, and it find data which is stale (has expired past TTL), it must refresh its cache by getting fresh information from an authoritative server.
  
  Note that TTL is a tuning factor, and it varies by DNS server. When you add a DNS address entry to your domain, unless you know what you're doing, accept the default TTL provided by the DNS Manager wizard.
• With "www.nitecruzr.net" referred by "CNAME" to "ghs.google.com", "ghs.google.com" is referred by "CNAME" to "ghs.l.google.com", and "ghs.l.google.com" referred by "A" to "72.14.207.121".
• To see this information in a real life GUI display, as setup with the GoDaddy DNS Hosting service (for instance), you may read Setting Up DNS Addresses For Custom Domains.

Note that, occasionally, you may see slightly different results than what you see above. There are a couple subtle syntactical conventions, involved in using the various DNS Manager wizards provided by the thousands of registrars all over the Internet, which periodically create challenges for us.

Also note that if you just updated DNS addresses, you may have to wait while your local DNS server is refreshed. If you run a Dig against the domain authority server, you can get up to date results instantly.

Regardless of its intricacies and weaknesses, Dig is one tool in my Custom Domain Diagnostic toolset - the one tool that I use most often, in my custom domain diagnostics.