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Identifying issues with and setting up name resolution on ESX/ESXi Server (1003735)

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  • Unable to configure VMware High Availability (HA).
  • Configuring VMware HA fails at about 97% completion.
  • Configuring VMware HA fails between 85 to 91%.
  • Reconfiguring VMware HA fails.
  • Adding an ESX host to a cluster fails.
  • Enabling VMware HA in a cluster fails.
  • These errors are generated when attempting to configure VMware HA:

    • An error occurred during configuration of the HA agent on the host
    • HA agent on <ESX> in cluster <cluster> in <Datacenter> has an error
    • Error: Cannot complete the configuration of the HA agent on the host. Other HA configuration error
    • cmd addnode failed for primary node:/opt/vmware/aam/bin/ft_startup failed

  • Host fails to remediate or exit Maintenance Mode.
  • You see these errors:
    • Operation timed out
    • Unable to connect to the MKS: Host address lookup for server failed: No such host is known

  • In the Tasks view of VirtualCenter/vCenter Server, you see the error:

    There are errors during the remediation operation
    Failed to find host

  • Update Manager is unable to scan ESX/ESXi hosts.
  • Host disconnects from the vCenter Server.
  • ESX/ESXi host enters a not responding state in the vCenter Server.

    Note: A common cause for an ESX/ESXi host dropping out of vCenter Server is due to the DNS (both forward and reverse) not functioning or configured correctly.


The errors listed in the Symptoms section are generated as a result of name resolution issues.
This article guides you through identifying issues with name resolution which can seriously impact the normal operation of ESX/ESXi, particularly in HA clustered environments. The article also details correctly configuring host files when there is no DNS server in the environment, or if the DNS server is incorrectly configured.


Identifying issues

There is a problem with name resolution if any of these tests fail. ESX/ESXi hosts must be able to find each other by:
  • IP address
  • Short Name
  • Fully Qualified Domain Name (FQDN)

If an issue with name resolution has been identified it must be resolved either on the DNS server or by using hosts files.

Note: After making any changes to DNS or hosts files, ensure that you delete the file /etc/FT_HOSTS (or /etc/opt/vmware/aam/FT_HOSTS and /var/run/vmware/aam/FT_HOSTS ) on all affected ESX/ESXi hosts.

  1. Verify that all ESX/ESXi hosts can ping each other by short name. All ESX/ESXi hosts in the environment must be able to ping each other by using short name only. For more information, see Testing network connectivity with the ping command (1003486).

  2. Verify that all ESX/ESXi hosts can nslookup each other.

    Use nslookup (reverse IP address lookup) to verify that the appropriate name is associated to a particular IP address.

    For example:

    [root@esx-server-1 /]# nslookup
    Address: name =

  3. Verify that all ESX/ESXi hosts can reverse nslookup each other.

    Use nslookup (forward IP address lookup) to verify that the appropriate IP address is associated to a particular name.

    For example:

    [root@esx-server-1 /]# nslookup esx-server-2


  4. Verify that the DNS server has both an A Record (Address Record) and a C NAME record (Canonical name record) configured for each ESX/ESXi hosts. 

Additional checks for VMware High Availability (HA) environments - ESX/ESXi 3.x and 4.x Only

Perform these additional checks for VMware High Availability environments with ESX/ESXi versions 3.x and 4.x (this does not apply to ESXi 5.0):

  1. Verify that the reported host name is in lowercase when you run:

    [root@esx-server-1 /]# hostname
    [root@esx-server-1 /]# hostname -s

  2. Verify that all host names in /etc/hosts are in lowercase.
  3. Verify that the search domain in /etc/resolv.conf is in lowercase.
  4. Verify that the host name in /etc/sysconfig/network is a fully qualified domain name, and is lowercase.
  5. Verify that the host name in /etc/vmware/esx.conf is a fully qualified domain name, and is lowercase.
  6. If your ESX/ESXi hosts are registered in DNS, verify that your system host name is lowercase and the record is a A name. Run this command to ensure the FQDN is resolvable and all lowercase:

    nslookup short_hostname

  7. Verify that all primary Service Consoles in the VMware HA cluster have the same name.
  8. Verify that all primary Service Consoles are in the same IP subnet.

Note: If a VMotion VMkernel port is on the same vSwitch as the primary Service Console, or if a host has multiple Service Consoles, see Incompatible HA Networks appearing when attempting to configure HA (High Availability) (1006541).

Configuring hosts files on ESX/ESXi

The hosts file on the ESX host is located at /etc/hosts .

Open the file for editing using a text editor such as nano or vi .

Example hosts file:

# Do not remove the following line, or various programs
# that require network functionality will fail. localhost.localdomain localhost

# Any line beginning with a pound sign is a comment and will not be read. esx-server-1 esx-server-2

# The VMware Virtual Center Server must also have an entry here virtualcenter

  • localhost must always be present in the hosts file. Do not modify or remove the entry for localhost .
  • The hosts file must be identical on all ESX/ESXi hosts in the cluster.
  • There must be an entry for every ESX/ESXi host in the cluster.
  • Every host must have an IP address, Fully Qualified Domain Name (FQDN), and short name.
  • The hosts file is case sensitive. Be sure to use lowercase throughout the environment.

    Note: This issue has been resolved in vCenter 2.5 U3 and above. For more information, see VMware HA Can Be Configured on a Cluster Regardless of the Letter Case of the ESX Server Host Names in the Resolved Issues section of the VirtualCenter 2.5 Update 3 Release Notes.


cannot-exit-maintenance-mode ha-fails host-fails-to-remediate name-resolution-esx name-resolution-issues

See Also

Update History

02/24/2011 - Updated to apply to 4.x and ESXi. 12/08/2011 - Added Forward IP and Reverse IP address lookup in steps 2 and 3. 06/05/2013 - Added additional error message

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  • 76 Ratings