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Search Results for: kickstart

Does ESXi Support DDNS (Dynamic DNS)?

08.01.2013 by William Lam // 5 Comments

An interesting feature request that was raised internally was for ESXi to support DDNS (Dynamic DNS) which allows a host client to update it's DNS record when using a DHCP Server. In most environments, to assign a hostname from DHCP, a DHCP reservation is used and this is maintained by the DHCP Server versus DDNS, where it is maintained by the client. Thanks to my colleague Eric Wager who did some quick research and found that ESXi does in fact supports DDNS and has been since ESXi 5.0.

I have not worked with DDNS much in the past and I have only seen it used for free/paid online services targeted at consumers to provide a well known address when their public IP Address changes frequently as with most ISPs. If your DHCP Server supports DDNS, this can be a handy feature to have, especially as you add new hosts you no longer have to manually create individual DNS record before hand and great for a lab environment. I did a big more digging to have a better understanding of how DDNS works with ESXi.

To enable support for DDNS on your ESXi host, you just need to set the hostname for the following ESXi Advanced Setting:

/Misc/PreferredHostName

You can do this in a variety of ways using either the vSphere Web/C# Client or using the command-line with ESXCLI.

Here is the syntax for the command:

esxcli system settings advanced set -o /Misc/PreferredHostName -s vesxi04.primp-industries.com

Once you have configured the setting, for the changes to go into effect, you will need to restart the management network. The easiest way to do this is via DCUI which you can run remotely by just typing dcui if you have an SSH session to your ESXi host. If you are using scripted install such as Kickstart, this can easily be automated as part of the post-install and upon first boot, DDNS will be enabled and configured with the proper hostname.

To test this in my lab environment, before enabling DDNS, I performed a reverse lookup of the assigned IP Address of my ESXi host from my DHCP server. In this example, the host received the address 192.168.1.135.

As you can see from the screenshot, a hostname could not be resolved as I would expect. After our changes, if we perform the reverse lookup again, we should now see the hostname that we had configured.

Another useful tidbit is the DHCP Client on ESXi is an ISC BIND implementation and this means if you require advanced things such as authentication keys, you can configured these options in /etc/dhclient-vmkX.conf where X is the specific VMkernel interface. For most deployments, you should not have to edit this file. Also if you want to prevent your DHCP Server from overriding the hostname of your ESXi host, you can add the following entry to the dhclient-vmkX.conf configuration file:

interface vmk0 {
   supersede host-name "vesxi04.primp-industries.com";
}

Just when I thought I knew about all the awesome features ESXi offers, it is a nice surprise to learn about another one!

Categories // Uncategorized Tags // ddns, dynamic dns, ESXi, ip address, ISC bind, mac address

How To Backup & Restore Free ESXi Host Configuration

02.15.2013 by William Lam // 23 Comments

ESXi host configurations can easily be backed up and restored using either the vCLI's vicfg-cfgbackup or PowerCLI's Get-VMHostFirmware cmdlet. These commands along with others that perform "write" operations are only supported when you have a (paid) licensed version of ESXi. If you are using free ESXi, the remote commands are only available for "read-only" operations. For more details, please refer to this article here.

Note: In my personal opinion, it is much quicker and more efficient to re-install ESXi and apply your configurations using either a scripted deployment such as kickstart or a combination along with post configuration scripts. Re-installs become extremely trivial when you centralize your ESXi host configurations, even for small setups.

Having said that, if you are running free ESXi in a small shop or in a home lab and wish to backup your ESXi host configurations, you can still do so by leveraging a neat little tool called vim-cmd found within the ESXi Shell. There is a section under hostsvc/firmware which manages the ESXi host configuration which also uses the same vSphere APIs that both vicfg-cfgbackup & Get-VMHostFirmeware command uses.

Under this section of vim-cmd, there are four commands:

  • backup_config   
  • reset_config    
  • restore_config  
  • sync_config

Prior to actually backing up your ESXi host configuration, run the following command which will flush the ESXi configuration changes:

vim-cmd hostsvc/firmware/sync_config

To backup the ESXi host configurations, run the following command which will generate a file that will be automatically stored in /scratch/downloads and can also be downloaded from a web browser using the URL shown from the output:

vim-cmd hostsvc/firmware/backup_config

Before restoring your ESXi host configurations, you will need to ensure the file is renamed to configBundle.tgz and stored under /tmp directory. You will also need to ensure the ESXi host is placed in maintenance mode by running the following command:

vim-cmd hostsvc/maintenance_mode_enter

To restore the ESXi host configurations, run the following command and specify the backup configuration file which should reside in /tmp/configBundle.tgz:

vim-cmd hostsvc/firmware/restore_config /tmp/configBundle.tgz

Note: Upon completing the restore, it will automatically reboot your ESXi host.

Here is a screenshot using the above commands to backup and then restore ESXi host:

Note: You can not restore an ESXi host using a configuration file backed up from a different host.

Categories // Uncategorized Tags // backup, ESXi, free esxi, get-vmhostfirmware, vicfg-cfgbackup, vim-cmd

Nested ESXi 5.1 Supports VMXNET3 Network Adapter Type

09.11.2012 by William Lam // 15 Comments

I noticed something interesting while extracting the contents of ESXi 5.1 ISO for some kickstart configurations ....

Do you see it? It's a VMXNET3 driver for the VMkernel! I also confirmed by running the following ESXCLI command querying for the VMkernel module "vmxnet3":

# esxcli system module get -m vmxnet3
Module: vmxnet3
Module File: /usr/lib/vmware/vmkmod/vmxnet3
License: GPL
Version: Version 1.1.32.0, Build: 799733, Interface: 9.2 Built on: Aug  1 2012
Signed Status:
Signature Issuer:
Signature Digest:
Signature FingerPrint:
Provided Namespaces:
Required Namespaces: [email protected], com.vmware.vmkapi@v2_1_0_0

***Disclaimer***: This is for educational purposes only, this is not officially supported by VMware. Use at your own risk. There is also a mention of this in the vSphere 5.1 release notes that VMs running on nested ESXi hosts using VMXNET3 driver could potentially crash. Again, not supported user at your own risk.

Next I decided to create a Nested ESXi 5.1 VM, but instead of selecting the e1000 driver which was the only network adapter type that would function for running a nested ESXi host, I choose the VMXNET3 adapter and to my surprise ESXi's networking stack was fully functional.

You can see from the above screenshot, I have a two VMXNET3 network adapters for my nested ESXi 5.1 VM. Here are two additional screenshot of the physical adapters as seen by nested ESXi 5.1 host and you can see that it shows up as VMware Inc. VMXNET3

I have not tried any performance tests, so not sure if there are going to be any significant benefits but pretty cool nonetheless!

Categories // Uncategorized Tags // ESXi 5.1, nested, vesxi, vmxnet3, vSphere 5.1

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William is Distinguished Platform Engineering Architect in the VMware Cloud Foundation (VCF) Division at Broadcom. His primary focus is helping customers and partners build, run and operate a modern Private Cloud using the VMware Cloud Foundation (VCF) platform.

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