Knowledge Base

KB Home / Web and Email Hosting

Externally Delegated DNS Configuration

Generally, GCom Internet does not support hosted sites with externally delegated DNS, unless those sites are controlled by authorised resellers. However, in all such cases, the following details set out the only acceptable methods of DNS zone record construction for domains with externally delegated DNS.

Under no circumstances should apex or other host records be hard coded by IP to point to one of our servers. We dynamically load balance down to the server level, and physically upgrade our hosting servers on a frequent basis. During such load balancing and upgrades, IP's assigned to individual sites and services will change. If a DNS zone outside of our control points to one of our servers directly by IP, the resolution for the client's site or service will fail whenever an IP is changed at the server level.

To work around this, we provide two dedicated host records on our cnames121.com domain for each externally delegated domain. We control these records internally to keep them in sync with the target server IP's at all times. As an example, for an externally delegated domain such as xyz.com.au, we would maintain records of the following form...

xyz-com-au-http.cnames121.com   A   123.123.123.123
xyz-com-au-smtp.cnames121.com   A   234.234.234.234

...where 123.123.123.123 is always set to the IP of the HTTP(S) services for the domain, and 234.234.234.234 is always set to the IP of the incoming SMTP services for the domain.

Important

Host records on our cnames121.com domain will not be created for any domain until/unless we receive email advice of an intention to delegate DNS externally. Such advice must be received directly from the recorded Administrative and Billing Contact of the hosting account.

Once the cnames121.com host records have been created at our end, all references of non apex host records in the client's externally delegated DNS zone should be made by CNAME to the appropriate record from above, and not by way of A records referencing the IP directly.

To remain RFC compliant, the apex record can only be handled with a CNAME approach if your DNS host is running advanced name servers which support ALIAS, ANAME or other CNAME flattening solutions. Unfortunately, many DNS hosts do not yet have this ability, so the apex often needs to be treated specially. There are 3 methods to handle the apex for externally delegated domains...

  1. For advanced DNS servers which internally provide CNAME flattening, the apex can be handled with an ALIAS/ANAME/CNAME record in the same way as the www host record.
  2. For systems where the hostmaster has full control of their DNS servers, a frequent cron should be run on the DNS servers to keep the apex synced with the www CNAME resolution within the zone record.
  3. For DNS systems with only basic functions, simply set the apex A record to 174.129.25.170 to use the free wwwizer service. Please note that this method is not compatible with websites redirecting the www to the apex. Such a configuration will cause an endless redirection loop. This method will also not allow https:// SSL/TLS on the apex directly.

The MX is easily handled by direct reference to the appropriate record from above.

Given the above, a typical snip of an externally delegated DNS zone record, using the wwwizer.com method of resolution for the apex, would look something like the following for the example xyz.com.au domain...

      A            174.129.25.170
      MX      10   xyz-com-au-smtp.cnames121.com.
ftp   CNAME        xyz-com-au-http.cnames121.com.
www   CNAME        xyz-com-au-http.cnames121.com.

 

KB Home / Web and Email Hosting

Scroll