vCenter Upgrade Pre-Check Fails: Reverse DNS (PTR) Record Missing for vCenter

Products

• VMware vCenter Server

Issue/Introduction

When preparing a vCenter for an upgrade (e.g., from vCenter 7.0U3 to 8.0), running the VDT (vCenter Diagnostic Tool) pre-check script is a crucial step. However, a common issue encountered during this pre-check is a failure related to DNS resolution, specifically concerning the reverse lookup of the vCenter's IP address.

The script output will typically indicate a successful port check and forward DNS resolution, but a clear failure for reverse DNS:

[FAIL] Forward and reverse DNS lookup for vcenter.xyz.local Reverse Lookup: a.a.a.a failed to resolve.

This is further verified by attempting direct nslookup commands:

Command> nslookup vcenter.xyz.local (shows successful forward lookup)
Name: vcenter.xyz.local
Address: a.a.a.a

Command> nslookup a.a.a.a (shows failed reverse lookup)
** server can't find b.b.b.in-addr.arpa: NXDOMAIN

This prevents the vCenter upgrade pre-check from completing successfully.

Environment

• vCenter 7.x
• vCenter 8.x

 

Cause

The root cause of the VDT pre-check failure is the absence of a proper PTR (pointer) record in the DNS server for the vCenter's IP address. While the forward DNS record (mapping hostname to IP) is correctly configured, the reverse DNS record (mapping IP to hostname) is missing or incorrectly configured in the DNS infrastructure.

vCenter and its associated tools, like VDT, rely heavily on robust and consistent DNS resolution for all its components, including both forward and reverse lookups, to ensure proper functionality and inter-service communication.

Resolution

To resolve the vdt pre-check failure and ensure proper DNS resolution for the vCenter, a correct PTR (pointer) record must be created or updated in the DNS infrastructure.

Recommended Action:

• Engage the DNS Team:  Collaborate with your organization's DNS administration team.
• Request PTR Record Creation: Request the creation of a PTR record for the vCenter's IP address (e.g., a.a.a.a) that correctly resolves to its Fully Qualified Domain Name (FQDN) (e.g., vcenter.xyz.local).
• Verify DNS Propagation: Once the DNS team confirms the record has been added, allow for DNS propagation time.
• Validate Resolution: From a system that utilizes the updated DNS server, verify the reverse DNS lookup using a command like nslookup <vCenter_IP_Address> (e.g., nslookup a.a.a.a). It should now return the vCenter's FQDN.
• Re-run vdt:  Execute the vdt pre-check script again. It should now pass the DNS resolution checks, allowing you to proceed with the vCenter upgrade.

By establishing the necessary reverse lookup record, the vCenter's network identity is fully and correctly established, meeting the prerequisites for a successful upgrade and contributing to overall environment stability.