DNS resolution

When you have a partial zone, Cloudflare handles DNS records a bit differently from full zones in order to internally resolve the origin server where proxied HTTP requests are sent to.

Records within the same zone

When you create a new DNS record in a partial zone, Cloudflare automatically checks whether any of your CNAME records point to existing A, AAAA, or CNAME records within the same zone.

For example, Cloudflare would show a warning if you had the following records in your partial zone:

sub1.partialzone.com   CNAME   sub2.partialzone.com
sub2.partialzone.com   A       192.0.2.1

Since Cloudflare contains both the CNAME and its target, our DNS resolution will send incoming HTTP requests to sub1.partialzone.com to the origin 192.0.2.1.

This can cause issues if you already have DNS records for sub2.partialzone.com at your authoritative DNS provider. These records may point to 192.0.2.4, another IP address, or another domain but - because Cloudflare contains the initial record and the target - it never queries your authoritative DNS provider for the record for sub2.partialzone.com.

    flowchart TD
      accTitle: DNS resolution flow with CNAME target in same partial zone
      A[Request to <code>sub1.partialzone.com</code>] --> B[<code>CNAME</code> record for <code>sub1.partialzone.com</code> to <code>sub2.partialzone.com</code>]
      subgraph Cloudflare
        B --> C[<code>A</code> record for <code>sub2.partialzone.com</code> to <code>192.0.2.1</code>]
      end
      C --> D[<code>192.0.2.1</code>]
      subgraph Authoritative DNS
      E[<code>A</code> record for <code>sub2.partialzone.com</code> to <code>192.0.2.4</code>]
      end

When you avoid this situation - meaning you do not have the target of the CNAME record within your partial zone - this DNS resolution would happen differently.

    flowchart TD
      accTitle: DNS resolution flow with CNAME target not in partial zone
      A[Request to <code>sub1.partialzone.com</code>] --> B[<code>CNAME</code> record for <code>sub1.partialzone.com</code> to <code>sub2.partialzone.com</code>]
      B --> C[<code>A</code> record for <code>sub2.partialzone.com</code> to <code>192.0.2.4</code>]
      C --> D[<code>192.0.2.4</code>]
      subgraph Cloudflare
        B
      end
      subgraph Authoritative DNS
        C
      end

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Records pointing to a partial zone within the same account

You could also create a CNAME record in a zone (partial or full setup) that points to a record in another partial zone within your account.

In this case, Cloudflare will always resolve the CNAME target based on the value at your authoritative DNS provider of the partial target zone.

    flowchart TD
      accTitle: DNS resolution flow with CNAME target in a zone within the same account
      A[Request to <code>www.alice.com</code>] --> B[<code>CNAME</code> record for <code>www.alice.com</code> to <code>www.partialzone.com</code>]
      B --> C[<code>A</code> record for <code>www.partialzone.com</code> to <code>192.0.2.4</code>]
      C --> D[<code>192.0.2.4</code>]
      subgraph Cloudflare account
        subgraph Cloudflare zone 1
          B
        end
        subgraph Cloudflare zone 2
        E[<code>A</code> record for <code>www.partialzone.com</code> to <code>203.0.113.1</code>]
        end
      end
      subgraph Authoritative DNS
      C
      end