NSX Manager UI intermittently displays cluster status as "Unavailable" or reports high management latency due to upstream DNS timeouts

Products

• VMware NSX

Issue/Introduction

In VMware NSX, the Manager user interface may intermittently report that one or more appliances are "Unavailable" or trigger false manager_cluster_latency_high alarms. While these alerts occur, the underlying appliance cluster status typically shows as healthy when verified directly.

• XXXX-XX-XXT16:53:03.467Z INFO RepoSyncStartUpThread-1780332767975 Utils 620999 - [nsx@6876 comp="nsx-manager" level="INFO" subcomp="manager"] getFqdnFromIp(): script returned FQDN: ;; communications error to <REDACTED_IP>#53: timed out
• 2026-06-01T16:53:03.468Z ERROR RepoSyncStartUpThread-1780332767975 IPv4Address 620999 - [nsx@6876 comp="nsx-manager" errorCode="MP260" level="ERROR" subcomp="manager"] Invalid ip string ';; communications error to <REDACTED_IP>#53: timed out'. Error parsing ';; communications error to <REDACTED_IP>'.
• 2026-06-01T16:53:04.611Z INFO RepoSyncStartUpThread-1780332767975 RepoSyncServiceImpl 620999 SYSTEM [nsx@6876 comp="nsx-manager" level="INFO" subcomp="manager"] Source Info : SourceInfo [protocol=https, managerIp=;; communications error to <REDACTED_IP>#53: timed out, nodeId=<REDACTED_UUID>, port=443, thumbprint=]

Environment

VMware NSX 4.x

Cause

The upstream DNS server fails to respond to reverse DNS lookup (PTR) queries for the NSX Manager appliance IP addresses. When the repository synchronization service (RepoSyncStartUpThread) attempts to resolve the IP addresses of cluster nodes, the queries time out. Instead of failing gracefully, the literal text of the network timeout error string is passed into downstream processing variables. This leads to parsing errors (such as errorCode="MP260") and stalls the internal API processing queues. When these synchronous API requests pile up, the user interface response is delayed past its default threshold, causing the UI to falsely mark the appliance cluster status as "Unavailable".

Resolution

To resolve this issue, ensure proper reverse DNS resolution is established for all appliances within the management cluster:

1. Configure PTR Records: Log into your authoritative DNS server and verify that valid Pointer (PTR) records exist in the appropriate Reverse Lookup Zones for all NSX Manager appliance IP addresses.

2. Verify Firewall Rules: Ensure that network security policies and firewalls permit bidirectional UDP and TCP traffic on port 53 between all NSX Manager management interfaces and the configured upstream DNS servers.

3. Validate Resolution from Appliance: SSH into each NSX Manager appliance as admin and test both forward and reverse lookups using the engineering or diagnostic shell tools (e.g., nslookup or dig) to ensure responses are instantaneous and free of communication timeouts.

4. Restart Management Services: To clear any hung repository synchronization threads or corrupted memory strings, log into each NSX Manager via SSH as admin and restart the management plane service:

   restart service manager