ESXi Hosts Disconnect from vCenter Due to Duplicate Loopback DNS Entries

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• vCenter Server and ESXi hosts. All hosts show as "Not responding" and VMs are in a disconnected state. Manually reconnecting hosts to vCenter is successful temporarily before they revert to "Not Responding".
  
  
• Reverse name resolution from vCenter to ESXi fails to get any authoritative answer:

  nslookup 198.51.100.1
  
  1.100.51.198.in-addr.arpa       name = ESXi.example.com
  
  Authoritative answers can be found from:

• Checking /var/log/vmware/vpxd/vpxd.log on the vCenter Server reveals heartbeat timeouts:

  info vpxd[06##9] [Originator@6876 sub=HostCnx opID=CheckforMissingHeartbeats-4f1###5f] [VpxdHostCnx] No heartbeats received from host; cnx: 5231cb53-1873-####-e##a-755#####ffd1, h: host-107###0, time since last heartbeat: 105697ms
  info vpxd[06##9] [Originator@6876 sub=InvtHostCnx opID=CheckforMissingHeartbeats-4f1###5f] Got lost connection callback for host-107###0
  warning vpxd[06##4] [Originator@6876 sub=InvtHostCnx opID=HostSync-host-107###0-50b6952a] Connection not alive due to missing heartbeats; [vim.HostSystem:host-107###0,ESXi.example.com], cnx: 5231cb53-1873-####-e##a-755#####ffd1
  info vpxd[06##4] [Originator@6876 sub=QuickStats opID=HostSync-host-107###0-50b6952a] Host [vim.HostSystem:host-107###0,ESXi.example.com] should not be polled
  warning vpxd[06##4] [Originator@6876 sub=MoHost opID=HostSync-host-107###0-50b6952a] host [vim.HostSystem:host-107###0,ESXi.example.com] connection state changed to NO_RESPONSE

• Checking /etc/resolv.conf on the vCenter Server shows a truncated configuration warning: # Too many DNS servers configured, the following entries may be ignored.

  nameserver 127.0.0.1
  nameserver 127.0.0.1
  nameserver 8.8.8.8
  # Too many DNS servers configured, the following entries may be ignored.
  nameserver 8.8.4.4

Environment

VMware vCenter Server 8.0.x

VMware vCenter Server 9.0.x

Cause

The administrator manually added the loopback IP (127.0.0.1) as a DNS server in the vCenter Server Appliance Management Interface (VAMI), this created duplicated nameserver 127.0.0.1 entries in /etc/resolv.conf, which exhausted the standard Linux limit of three nameservers.

Consequently, the operating system ignored valid external DNS entries, leading to reverse lookup and heartbeat validation failures.

Resolution

1. Log into the vCenter Server Virtual Appliance Management Interface (VAMI) at https://vCenter.example.com:5480.
   
   
2. Navigate to the Networking configuration and edit the DNS servers.
   
   
3. Remove the manual entry for the loopback address (127.0.0.1).
   
   
4. Ensure only valid external DNS servers (e.g., 8.8.8.8, 8.8.4.4) are configured.
   
   
5. Save the configuration.
   
   
6. Verify via SSH that /etc/resolv.conf on the vCenter Server no longer contains duplicate 127.0.0.1 entries and correctly lists the external DNS servers without the "Too many DNS servers configured" warning.