Identifying issues with and setting up DNS name resolution on ESXi Server
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Identifying issues with and setting up DNS name resolution on ESXi Server
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Article ID: 310760
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Updated On: 06-30-2025
Products
VMware vSphere ESXi
Issue/Introduction
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 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.
Symptoms:
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 ESXi 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
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
From the vCenter webclient you might see this error: vSphere HA host status
Update Manager is unable to scan ESXi hosts.
Host disconnects from the vCenter Server.
ESXi host enters a not responding state in the vCenter Server.
Example of ESXi vpxa.log output:
####-##-##T##:##:##.###Z warning vpxa[123456] [Originator@1234 sub=IO.Connection] Failed to resolve localhost IP address; localhost(IPv6), e: 1(Host not found (authoritative))
Example of vCenter vpxd.log output:
####-##-##T##:##:##.###Z warning vpxd[456789] [Originator@1234 sub=IO.Connection opID=<opID>] Failed to resolve address; <resolver p:0x0000000000000000, '<host_FQDN>:443', next:(null)>, e: 1(Host not found (authoritative)), async: true, duration: 0msec
Note: A common cause for an ESXi host dropping out of vCenter Server is due to the DNS (both forward and reverse) not functioning or configured correctly.
Environment
VMware ESXi 7.x VMware ESXi 8.x
Resolution
Identifying issues
There is a problem with name resolution if any of these tests fail. 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.
Verify that all ESXi hosts can ping each other by short name. All ESXi hosts in the environment must be able to ping each other by using short name only.
Verify that all ESXi hosts can nslookupeach other.
Use nslookup(reverse IP address lookup) to verify that the appropriate name is associated to a particular IP address.
Verify that the DNS server has both an A Record (Address Record) and a C NAME record (Canonical name record) configured for each ESXi hosts.
5. Verify that the managing vCenter does not have any improper entries in its "/etc/hosts/" file for the targeted ESXi host.
Configuring hosts files on ESXi
The hosts file on the ESX host is located at /etc/hosts.
Open the file for editing using a text editor such as nanoor vi.
Example hosts file:
# Do not remove the following line, or various programs # that require network functionality will fail. 127.0.0.1 localhost.localdomain localhost
# Any line beginning with a pound sign is a comment and will not be read. 192.168.x.x esx-server-1.example.com esx-server-1 192.168.x.x esx-server-2.example.com esx-server-2
# The VMware Virtual Center Server must also have an entry here 192.168.x.xx virtualcenter.example.com virtualcenter
Notes:
localhostmust always be present in the hosts file. Do not modify or remove the entry for localhost.
The hosts file must be identical on all ESXi hosts in the cluster.
There must be an entry for every 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.