CNAME pointing to external subdomain not resolving

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I'm attempting to get domain-b to direct to domain-a and feel like I've done it via a CNAME to a pretty standard method. Yet I'm still getting ERR_NAME_NOT_RESOLVED / server DNS address could not be found when trying www.domain-b.com.

Various DNS diagnostic sites suggest, after 24 hours, that DNS caches throughtout the world are up-to-date with my latest DNS records, which are as follows (and with the same registrar, though this shouldn't be necessary and may likely not be in the future):

Domain-B

    A       1.2.3.4 # re-direct root domain to www via registrar's own suggested method (IP just an example)    
www CNAME   domains.domain-a.com    
    MX      email.com   10
    MX      relay.email.com     20      
    TXT     v=spf1 include:email.com -all

Domain-A

    A       IP Address of server    
*   A       IP Address of server    
    MX      email.com   10
    MX      relay.email.com     20      
    TXT     v=spf1 include:email.com -all

While I need the catchall wildcard A Record for Domain-A for other reasons, I did try an explicit A Record of the domains subdomain and it didn't improve the situation.

  • domain-a.com resolves fine

  • All subdomains to domain-a.com resolve fine

  • domain-b.com redirects to www.domain-b.com com fine

  • www.domain-b.com (whether direct or via domain-b.com redirect) always
    returns a DNS address not found error in all browsers.

Have I overlooked something in my DNS records or should I be searching elsewhere for the culprit? I can visit domains.domain-a.com directly no problem so this leads me to believe it's not an error with any DNS records between my server host and domain-a DNS records.

Best Answer

The DNS records were fine and it turns out my ISP is just badly delayed in updating its DNS caches, despite low TTL numbers in my records. It was my lack of experience with the nslookup tool that made me miss this. I saw nothing unusual with the results, returning Got SERVFAIL reply as expected.

I didn't know you could use nslookup to run the same test from a different DNS server, and they all returned the result without a fail. I'd assumed that if other DNS global server checks were showing the records correctly in 95% of servers, my own ISP surely wouldn't be the culprit. Lesson learned. Thanks to @HBruijn for prompting me to revisit nslookup.

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