---
name: cis-cname-dns-resolution
title: DNS resolution in partial (CNAME) configuration
description: When you create a new DNS record in a partial zone, CIS automatically checks whether any of your CNAME records point to existing A, AAAA, or CNAME records within the same zone.
last-updated: 2025-01-14
---

> ## Documentation Index
> The table of contents for this documentation set is at https://cloud.ibm.com/docs/cis?format=markdown
> The index for all IBM Cloud docs is at: https://cloud.ibm.com/docs/llms.txt
> Use these files to discover more information as needed.

# DNS resolution in partial (CNAME) configuration
{: #dns-resolution-in-cname-config}
 
In a partial (CNAME) configuration, CIS handles DNS records a bit differently from full zones to internally resolve the origin server where proxied HTTP requests are sent to.

## Records within the same zone
{: #records-in-same-zone}

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

For example, CIS shows a warning if you have the following records in your partial zone:

```text
sub1.partialzone.com   CNAME   sub2.partialzone.com
sub2.partialzone.com   A       192.0.2.1
```
{: screen}

Because CIS contains both the CNAME and its target, the DNS resolution sends 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 might point to `192.0.2.4`, another IP address, or another domain. However, because CIS contains the initial record and the target, it never queries your authoritative DNS provider for the record for `sub2.partialzone.com`.

![Path without authoritative DNS](images/dns-resolution1.svg "DNS request path no authoritative dns"){: caption="Path a request takes without passing through an authoritative DNS" caption-side="bottom"}

If you don't have the target of the CNAME record within your partial zone this DNS resolution happens differently.

![Path with authoritative DNS](images/dns-resolution2.svg "DNS request path with authoritative dns"){: caption="Path a request takes passing through an authoritative DNS" caption-side="bottom"}

## Records pointing to a partial zone within the same account
{: #records-partial-zone-same-account}

You can 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, CIS always resolves the CNAME target based on the value at your authoritative DNS provider of the partial target zone.

![Path within same account](images/dns-resolution3.svg "DNS request path within the same account"){: caption="Path a request takes within the same account" caption-side="bottom"}