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DNS: CNAME to enable www on subdomains

I currently have a domain example.com and a subdomain sub.example.com. What I am trying to do is to make them accessible with www, that is, www.example.com and www.sub.example.com. The records look like this (using Namecheap here so not editing the raw zone-file)

Type   Host          Value
A      @             <ip-addr>
A      sub           <ip-addr>
CNAME  www           example.com.
CNAME  www           sub.example.com.

While example.com, sub.example.com and www.example.com is accessible, www.sub.example.com isn't, what am I doing wrong?

Solution

  • You need:

    CNAME  www.sub           example.com.

    Explanation:

    (since the domain is example.com, it will be appended to any Host not ending with .)

    A @ <ip-addr> means example.com=<ip-addr>

    A sub <ip-addr> means sub.example.com=<ip-addr>

    CNAME www example.com. means www.example.com=example.com
    (resulting in www.example.com=<ip-addr>)

    CNAME www sub.example.com. means www.example.com=sub.example.com
    (resulting again in www.example.com=<ip-addr>, so this last one is obviously rendundant and can be removed)

    So, you have no www.sub.example.com defined anywhere, and any one of these would work:

    CNAME  www.sub           example.com.
CNAME  www.sub           sub.example.com.
CNAME  www.sub           www.example.com.
A      www.sub           <ip-addr>