Why is the host command returning both an A and a CNAME record

cachedomain-name-system

We have a zone with a 2 hour TTL. Previous to making any changes it returned an A record when looking up the entry for www.

We changed the entry for www to point to a CNAME record. After the change, we noticed that the host command was returning both a CNAME and an A record as shown:

user@osx:~$ host www.example.com
www.example.com has address 192.168.1.2
www.example.com is an alias for vip.example.com.
www.example.com is an alias for vip.example.com.
user@osx:~$

Was this a problem with some DNS servers caching? If we had simply let the TTL fully expire, would we have gotten a CNAME as expected with no A record?

I didn't get any more detailed information with dig or other commands.

EDIT: The true address for vip.example.com. is completely different from the A record that was originally returned:

user@osx:~$ host vip.example.com
vip.example.com has address 172.16.4.5
user@osx:~$

Best Answer

Does a dig +trace show anything? It should show how it comes to the response you're getting.

Related Solutions

DNS – Multiple A Records vs Single A Record with CNAMEs

There are two alternate views of this question, and it's one that is ultimately going to be debated forever. I'm not going to give my opinion (because I'm torn myself), but the general arguments each way typically are:

You should define A records for your physical machines, and then CNAME services onto those machines. This does make it rather clear as to what is what, and in the event that you need to renumber there's not a lot of records to change -- just the machine records. On the other hand, it does increase your DNS lookup load somewhat, and "auxiliary" IPs (think SSL vhosts) don't fit neatly into this model.
The literal meaning of "canonical name" (CNAME) is to define strict aliases of the same name (think mail and smtp), and if you have multiple services running on the same machine they should all have A records, because it reduces load on DNS and some services (NS records and, to a lesser extent, MX records) really aren't impressed with dealing with CNAMEs, so if you have to handle those services differently anyway, we may as well do it for everything.

Wildcard ‘A’ record overriding CNAME record

The more specific DNS record overrides the wildcard. So your CNAME should override your wildcard A. What this might be is that you still have the domain name cached to the a record. Use the dig command:

dig @yourdnsserver mydomain.freshdesk.com

Normally it should return the CNAME.

Best Answer

Related Solutions

DNS – Multiple A Records vs Single A Record with CNAMEs

Wildcard ‘A’ record overriding CNAME record

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