slaubstein
Contributor
Contributor

DNS usage by ESX hosts

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I am curious as to how important dns entries are on esx hosts(configuration DNS&Routing tabs) as we are changing all our dns servers. Will i need to reboot the ESX host if i change the ip's or is the service network restart or simliar command good enough? All the vm's have the dns entires so i am not sure what the hosts even need the entries for. This is on Vsphere 4.

thanks

stuart

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a_p_
Leadership
Leadership

If you are running stand alone hosts, the DNS is not important. However, if you are running the hosts in a vCenter environment you have to make sure the DNS resolution works. Otherwise you will experience issues with hosts disconnecting from vCenter and HA not working anymore.

The DNS entries can be modified on the fly, which means that you could enter the new DNS servers in addition to the current ones and once the new DNS servers are in place, remove the old entries.

André

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a_p_
Leadership
Leadership

If you are running stand alone hosts, the DNS is not important. However, if you are running the hosts in a vCenter environment you have to make sure the DNS resolution works. Otherwise you will experience issues with hosts disconnecting from vCenter and HA not working anymore.

The DNS entries can be modified on the fly, which means that you could enter the new DNS servers in addition to the current ones and once the new DNS servers are in place, remove the old entries.

André

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RParker
Immortal
Immortal

Will i need to reboot the ESX host if i change the ip's or is the service network restart or simliar command good enough?

Moving a DNS server is one thing, a DNS outage is another. CHANGING DNS entries is the one that should be of concern. ESX doesn't really care about DNS, but vCenter DOES, since that's how it talks to the ESX hosts.

If you use IP, DNS isn't important. If IP addresses change, DNS works better, provided DNS server gets updated properly. So it's no important from a host perspective, but it is from backpup, management, and update and other add-ons. The register with vCenter, and if this information isn't accurate, the ESX hosts are missing.

You never really HAVE to reboot a host. If you can get to the console of the machine you can reset the IP and DNS if needed.

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slaubstein
Contributor
Contributor

Ah ok so if i change one of the 2 possible dns entries on my esx host to the ip of the new dns server then it will have availability no matter what during the transition. As a follow on question then since all my DNS servers are on VM's is there anything i should be worried about for HA etc since i have no physical DNS at all. Perhaps i could at least use one of the dns entries to point to a vm running dns that is on s separate cluster?

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athlon_crazy
Virtuoso
Virtuoso

Well, it's resolve hostname lookup among your ESX hosts. If you configured VMware HA using fqdn, your hosts may not able to contact your primary HA hosts and this could initiate HA failover.

Please take a look this KB on how to change the DNS.

http://www.no-x.org
a_p_
Leadership
Leadership

... since all my DNS servers are on VM's is there anything i should be worried about for HA ...

In this case you should probably configure anti affinity rules to make sure your DNS servers always run on different ESX hosts.

André

slaubstein
Contributor
Contributor

i found this on the vmware so am not sure if i need a reboot or not-i wont change anything but the ip's of the DNS servers.

and andre thanks for the affinity idea

Changing settings in VMware vSphere or Infrastructure Client

To change the hostname, domain, DNS servers, and default gateway in VMware vSphere or Infrastructure (VI) Client:

Highlight the ESX host and click the Configuration tab.

Click DNS and Routing.

Click Properties.

To change the hostname, domain, and DNS servers, click the DNS Configuration tab and enter the appropriate values.

Note: Disable VMware High Availability if you do not want virtual machines to failover during the hostname IP change.

To change the default gateway, click the Routing tab and enter the appropriate value.

Reboot the ESX host for the changes to take effect.

Reconnect the ESX host to vCenter Server with the new IP address.

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