ESXi Host FQDN Validation Fails due to DHCP Option 15 Trailing Dot

Products

• VMware vSphere ESXi

Issue/Introduction

When an ESXi host is configured to use DHCP on its management interface (vmk0), the ESXi DHCP client (dhclient-vmk0) may fail to sanitize trailing dots from the domain name returned in DHCP Option 15 (Domain Name) and Option 119 (Domain Search List).

This behavior causes the host to apply the trailing dot to its runtime FQDN (e.g., hostname.testdomain.), which subsequently triggers validation failures in downstream services like vCenter Server host registration or VCF API validation.

• ESXi host FQDN appears with a trailing dot (e.g., esx-01.domain.name.) when queried via esxcli system hostname get.
• Downstream API validations (such as VCF SddcHostSpec regex) reject the host identity.
• Error message or validation failure indicating "invalid characters" in the hostname or domain.
• The /etc/dhclient-vmk0.leases file contains the trailing dot in the option domain-name or option domain-search fields.

Environment

VMware Cloud Foundation
VMware ESX

Cause

Client operating systems trust and apply DHCP payload strings as received without performing string sanitization. While RFC 1034 allows trailing dots within DNS server zone files to denote an absolute root domain, local operating system hostnames and domain strings are strictly governed by RFC 1123. Under RFC 1123, a trailing dot represents an illegal empty label at the end of the hostname string, causing character validation and regex parsing errors across downstream VMware API services and scripts.

Resolution

1. Remediate DHCP Server Configuration (Primary Solution): Update the DHCP server scope/options (Option 15 and Option 119) to strip the trailing dot from the domain string (e.g., update "trailingdot.domain." to "trailingdot.domain").

2. Refresh Client Lease: Renew the DHCP lease on the affected ESXi host (esxcli network ip interface ipv4 set -i vmk0 -t dhcp) or reboot the host to apply the corrected domain payload.

3. Static Configuration (Alternative Workaround): If the DHCP configuration cannot be immediately modified, temporarily assign a static IP address and FQDN without trailing dots on the ESXi host management interface (vmk0).