Category: VMware

ESXi is the hypervisor in a vSphere environment. The hypervisor provides physical hardware resources dynamically to virtual machines as needed to support the operation of the virtual machines. The hypervisor allows virtual machines to operate with a degree of independence from the underlying physical hardware. For example, a virtual machine can be moved from one physical host to another, or its virtual disks can be moved from one type of storage to another, without affecting the functioning of the virtual machine.
Because virtual machines are decoupled from specific underlying physical hardware, virtualization allows you to consolidate physical computing resources such as CPUs, memory, storage, and networking into pools of resources that can be dynamically and flexibly made available to virtual machines. With appropriate management software, such as vCenter Server, you can also use a number of features that increase the availability and security of your virtual infrastructure.

Clone Operation (New-VM) and Storage vMotion(Move-VM)

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In VMware PowerCLI, New-VM and Move-VM are two distinct cmdlets used for different purposes related to virtual machines. VAAI (vStorage APIs for Array Integration) is a VMware feature that offloads certain storage operations to the storage array to improve performance and efficiency. While VAAI is not directly related to the New-VM and Move-VM cmdlets, I will provide examples of how these cmdlets are used, and then explain the relationship between VAAI and storage operations.

  1. New-VM: The New-VM cmdlet is used to create a new virtual machine (VM) within a specified host or cluster. It allows you to define various configuration settings for the new VM, such as the VM name, guest operating system, CPU, memory, disk, network settings, and more.

Example of New-VM:

# Create a new virtual machine
New-VM -Name "NewVM" -VMHost "ESXiHost" -Datastore "Datastore1" -MemoryGB 4 -NumCPU 2 -NetworkName "VM Network" -DiskGB 50

In this example, the New-VM cmdlet is used to create a new VM named “NewVM” on the host “ESXiHost,” with 4GB of memory, 2 CPUs, connected to the “VM Network” for networking, and a 50GB virtual disk on “Datastore1.”

  1. Move-VM: The Move-VM cmdlet is used to migrate a VM from one host or datastore to another. It allows you to perform live migrations (vMotion) or cold migrations (Storage vMotion) of VMs across hosts or datastores in a vSphere environment.

Example of Move-VM:

# Migrate a virtual machine to a different datastore
Move-VM -VM "MyVM" -Datastore "NewDatastore"

In this example, the Move-VM cmdlet is used to migrate the VM named “MyVM” to a different datastore named “NewDatastore.”

Now, let’s briefly discuss VAAI:

VAAI (vStorage APIs for Array Integration): VAAI is a set of APIs provided by VMware that allows vSphere to offload certain storage operations from the ESXi hosts to the storage array. This offloading improves performance and efficiency by leveraging the capabilities of the underlying storage hardware.

Examples of storage operations offloaded to VAAI-enabled storage arrays include:

  • Hardware Accelerated Copy (HWCOPY): Improves VM cloning and snapshot operations by using the storage array to perform data copies.
  • Zero Block Detection (Zero): Allows the storage array to automatically handle zeroed-out blocks, reducing the burden on the ESXi host and improving storage efficiency.
  • Full Copy (HWFCOPY): Facilitates storage vMotion by performing fast and efficient data movement between datastores using the storage array’s capabilities.

In VMware PowerCLI, the Move-VM cmdlet automatically leverages VAAI (vStorage APIs for Array Integration) if the underlying storage array supports VAAI and the necessary VAAI primitives are enabled. VAAI allows the storage array to offload certain storage operations, making VM migrations faster and more efficient. Let’s take a look at an example of using Move-VM with VAAI:

# Connect to vCenter Server
Connect-VIServer -Server "vcenter.example.com" -User "username" -Password "password"

# Define the source VM and its current datastore
$sourceVM = Get-VM -Name "MyVM"
$sourceDatastore = Get-Datastore -VM $sourceVM

# Define the destination datastore
$destinationDatastore = Get-Datastore -Name "NewDatastore"

# Perform the VM migration using VAAI (Storage vMotion)
Move-VM -VM $sourceVM -Datastore $destinationDatastore -Force -DiskStorageFormat Thin

# Disconnect from vCenter Server
Disconnect-VIServer -Server "vcenter.example.com" -Confirm:$false

In this example, we perform a Storage vMotion using the Move-VM cmdlet with VAAI. Here’s what each step does:

  1. We start by connecting to the vCenter Server using Connect-VIServer.
  2. We define the source VM ($sourceVM) for the migration and get the current datastore ($sourceDatastore) where the VM is located.
  3. Next, we define the destination datastore ($destinationDatastore) where we want to move the VM.
  4. Finally, we use the Move-VM cmdlet to perform the VM migration. The -DiskStorageFormat Thin parameter specifies that the virtual disks should be moved with thin provisioning. The -Force parameter is used to suppress any confirmation prompts during the migration.

The Move-VM cmdlet will automatically utilize VAAI primitives if they are supported and enabled on the underlying storage array. VAAI accelerates the data movement between datastores, resulting in faster and more efficient VM migrations.

Re-IP’ing ESXi hosts in vCenter using a PowerShell script

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Re-IP’ing ESXi hosts in vCenter using a PowerShell script involves several steps and should be handled with caution, as it can disrupt the virtualized environment. The following script assumes you have VMware PowerCLI installed and connected to your vCenter server.

Before running the script, ensure you have a backup of your current configuration, and understand the implications of re-IP’ing your ESXi hosts.

# Connect to vCenter server
Connect-VIServer -Server YOUR_VCENTER_SERVER -User YOUR_USERNAME -Password YOUR_PASSWORD

# Define the old and new IP addresses
$oldIP = "OLD_IP_ADDRESS"
$newIP = "NEW_IP_ADDRESS"
$subnetMask = "NEW_SUBNET_MASK"
$gateway = "NEW_GATEWAY"

# Retrieve all ESXi hosts managed by vCenter
$esxiHosts = Get-VMHost

# Reconfigure network settings for each ESXi host
foreach ($esxiHost in $esxiHosts) {
    Write-Host "Reconfiguring network settings for $($esxiHost.Name)..."
    $esxiHostNic = Get-VMHostNetworkAdapter -VMHost $esxiHost | Where-Object { $_.Type -eq "Management" }

    # Set new IP address, subnet mask, and gateway
    $esxiHostNic | Set-VMHostNetworkAdapter -IP $newIP -SubnetMask $subnetMask -Gateway $gateway -Confirm:$false

    # Test the new connection and make sure it is responding
    if (Test-Connection -ComputerName $newIP -Count 1 -Quiet) {
        Write-Host "ESXi host $($esxiHost.Name) has been reconfigured successfully."
    } else {
        Write-Host "Failed to reconfigure ESXi host $($esxiHost.Name). Please verify the new network settings manually."
    }
}

# Disconnect from vCenter server
Disconnect-VIServer -Server $null

Replace the placeholders YOUR_VCENTER_SERVER, YOUR_USERNAME, YOUR_PASSWORD, OLD_IP_ADDRESS, NEW_IP_ADDRESS, NEW_SUBNET_MASK, and NEW_GATEWAY with appropriate values.

This script will loop through all ESXi hosts managed by vCenter, reconfigure the network settings for the management interface with the new IP address, subnet mask, and gateway, and then test the new connection to ensure it is responsive.

Again, exercise extreme caution when using this script, and always have a backup and a rollback plan ready before making any changes to your production environment.

To check and generate a report of backup, cloning, snapshot, or any other task of VM/ESXi/datastore in vSphere using PowerCLI

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  1. Install VMware PowerCLI: If you haven’t installed VMware PowerCLI yet, download and install it from the official VMware website: https://code.vmware.com/web/dp/tool/vmware-powercli/12.5.0
  2. Connect to vCenter Server: Open PowerShell or PowerShell ISE and connect to your vCenter Server using the Connect-VIServer cmdlet. Replace 'YOUR_VCENTER_SERVER' with the IP address or FQDN of your vCenter Server:
Connect-VIServer -Server 'YOUR_VCENTER_SERVER' -User 'YOUR_USERNAME' -Password 'YOUR_PASSWORD'

Generate the report for tasks: You can use the Get-VIEvent cmdlet in PowerCLI to retrieve events and filter them based on the task type (e.g., backup, clone, snapshot, etc.). Here’s a PowerShell script to generate the report:

# Define the output file path for the report
$outputFile = "C:\Path\To\Your\Report.txt"

# Get all VMs
$vms = Get-VM

# Initialize an empty array to store the events
$taskEvents = @()

# Get events for each VM and filter the ones related to tasks (backup, clone, snapshot, etc.)
foreach ($vm in $vms) {
    $events = Get-VIEvent -Entity $vm | Where-Object { $_.GetType().Name -match "TaskEvent" }
    $taskEvents += $events
}

# Generate a report and write it to the output file
$report = @()

foreach ($event in $taskEvents) {
    $vmName = $event.Vm.Name
    $eventType = $event.GetType().Name
    $eventFullType = $event.GetType().FullName
    $eventCreated = $event.CreatedTime
    $eventUserName = $event.UserName
    $eventFullData = $event | Format-List | Out-String

    $reportLine = @"
VM Name: $vmName
Event Type: $eventType
Event Full Type: $eventFullType
Event Created: $eventCreated
Event User Name: $eventUserName
Event Details:
$eventFullData
"@

    $report += $reportLine
}

# Save the report to the output file
$report | Out-File -FilePath $outputFile

# Display success message
Write-Host "Report generated successfully. Check $outputFile for the report."

Disconnect from vCenter Server: After generating the report, it’s a good practice to disconnect from the vCenter Server using the Disconnect-VIServer cmdlet:

Disconnect-VIServer -Server 'YOUR_VCENTER_SERVER' -Force -Confirm:$false

Please make sure to replace 'YOUR_VCENTER_SERVER', 'YOUR_USERNAME', and 'YOUR_PASSWORD' in the script with your vCenter server details. Additionally, modify the $outputFile variable to specify the path and filename for the generated report. The script will search for task-related events for each VM, extract relevant details, and save the report to the specified output file.

Get the maximum size of VMDKs (Virtual Machine Disk) in a vCenter environment

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To get the maximum size of VMDKs (Virtual Machine Disk) in a vCenter environment using PowerCLI and print the information to a file, you can use the following PowerShell script:

# Connect to the vCenter Server
Connect-VIServer -Server vcenter.example.com -User administrator -Password your_password

# Output file path to save the results
$outputFile = "C:\Path\To\Output\File.txt"

# Get all VMs in the vCenter
$allVMs = Get-VM

# Create an empty array to store the maximum VMDK sizes
$maxVmdkSizes = @()

# Loop through each VM and get the maximum size of its VMDKs
foreach ($vm in $allVMs) {
    $vmdks = Get-HardDisk -VM $vm
    $maxVmdkSizeGB = $vmdks | Measure-Object -Property CapacityGB -Maximum | Select-Object -ExpandProperty Maximum
    $maxVmdkSizes += [PSCustomObject]@{
        "VM Name" = $vm.Name
        "Maximum VMDK Size (GB)" = $maxVmdkSizeGB
    }
}

# Export the results to a CSV file
$maxVmdkSizes | Export-Csv -Path $outputFile -NoTypeInformation

# Disconnect from the vCenter Server
Disconnect-VIServer -Server vcenter.example.com -Confirm:$false

Write-Host "Maximum VMDK sizes have been saved to $outputFile."

In this script, replace "vcenter.example.com" with the hostname or IP address of your vCenter Server. Also, provide the correct path for $outputFile to save the results.

The script connects to the vCenter Server using Connect-VIServer, retrieves all VMs using Get-VM, and then loops through each VM to get the VMDKs using Get-HardDisk. It calculates the maximum VMDK size in gigabytes (GB) using Measure-Object, stores the results in the $maxVmdkSizes array as a custom PowerShell object, and finally exports the results to a CSV file using Export-Csv.

The script then disconnects from the vCenter Server using Disconnect-VIServer. The maximum VMDK sizes for each VM are saved in the specified output file, and a message is displayed on the PowerShell console to indicate the completion of the script.

To get the maximum size VMDKs in a vCenter environment and print them to a file using Python, you’ll need to use the VMware vSphere API. We can achieve this by using the pyVmomi library, which is a Python SDK for the VMware vSphere API. First, you’ll need to install the pyVmomi library:

pip install pyVmomi

Next, you can use the following Python script to connect to your vCenter server, retrieve the virtual machines, and find the largest VMDK size for each VM:

from pyVim.connect import SmartConnect, Disconnect
from pyVmomi import vim
import ssl

def get_max_vmdk_size(virtual_machine):
    max_vmdk_size = 0
    for device in virtual_machine.config.hardware.device:
        if isinstance(device, vim.vm.device.VirtualDisk):
            size_bytes = device.capacityInBytes
            if size_bytes > max_vmdk_size:
                max_vmdk_size = size_bytes
    return max_vmdk_size

def main():
    # Set your vCenter server details
    vcenter_server = 'YOUR_VCENTER_SERVER'
    username = 'YOUR_USERNAME'
    password = 'YOUR_PASSWORD'

    # Ignore SSL certificate verification
    context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
    context.verify_mode = ssl.CERT_NONE

    try:
        # Connect to vCenter
        service_instance = SmartConnect(host=vcenter_server, user=username, pwd=password, sslContext=context)
        if not service_instance:
            raise SystemExit("Unable to connect to vCenter server.")

        # Get all virtual machines in the vCenter environment
        content = service_instance.RetrieveContent()
        container = content.rootFolder
        viewType = [vim.VirtualMachine]
        recursive = True
        containerView = content.viewManager.CreateContainerView(container, viewType, recursive)
        virtual_machines = containerView.view

        # Find the maximum size VMDK for each virtual machine
        vm_max_vmdk_sizes = {}
        for virtual_machine in virtual_machines:
            vm_max_vmdk_sizes[virtual_machine.name] = get_max_vmdk_size(virtual_machine)

        # Print the results to a file
        with open('max_vmdk_sizes.txt', 'w') as f:
            for vm_name, max_vmdk_size in vm_max_vmdk_sizes.items():
                f.write(f"{vm_name}: {max_vmdk_size / (1024 ** 3)} GB\n")

        print("Maximum VMDK sizes saved to 'max_vmdk_sizes.txt'.")

    except Exception as e:
        print("Error:", e)

    finally:
        # Disconnect from vCenter
        if service_instance:
            Disconnect(service_instance)

if __name__ == "__main__":
    main()

Replace 'YOUR_VCENTER_SERVER', 'YOUR_USERNAME', and 'YOUR_PASSWORD' with your vCenter server details. The script will connect to your vCenter server, retrieve all virtual machines, find the largest VMDK size for each VM, and then print the results to a file named max_vmdk_sizes.txt in the same directory as the script. The VMDK sizes will be printed in gigabytes (GB).

Virtual Machine (VM) running on VMware ESXi is not getting an IP address

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When a virtual machine (VM) running on VMware ESXi is not getting an IP address, it indicates a network connectivity issue. Troubleshooting this problem involves checking various settings and configurations to identify the root cause. Here are some common steps to troubleshoot a VM not getting an IP address on ESXi:

1. Verify Network Adapter Configuration:

  • Ensure that the VM has a network adapter attached and that it is connected to the correct virtual switch in ESXi.
  • Check the network adapter settings within the VM’s operating system. Ensure that it is set to obtain an IP address automatically (DHCP) unless you have a specific reason to use a static IP address.

2. Check DHCP Server:

  • Ensure that the DHCP server is operational and running in the network.
  • Check if there are enough available IP addresses in the DHCP pool to assign to the VM.
  • If the DHCP server is a separate virtual machine, ensure it is running and reachable from the VM.

3. Check VLAN and Network Segmentation:

  • If VLANs are used in the network, verify that the VM is on the correct VLAN and that the virtual switch is properly configured to handle VLAN tagging.
  • If the network is segmented, ensure that the VM is placed in the correct network segment and has the appropriate network access.

4. Check ESXi Networking Settings:

  • Verify that the ESXi host has functional network connectivity. Check the physical NICs, virtual switches, and port group configurations.
  • Check the VMkernel adapters used for management and VMotion to ensure they are functioning correctly.

5. Check Security Settings:

  • If there are any firewall or security settings in place, ensure that they are not blocking DHCP traffic or VM network communication.

6. Verify MAC Address:

  • Make sure that there are no conflicts with the MAC address of the VM’s network adapter. Duplicate MAC addresses can cause IP assignment issues.

7. Restart VM and Network Services:

  • Try restarting the VM and see if it acquires an IP address upon boot.
  • If the issue persists, try restarting the network services on the ESXi host.

8. Check Logs:

  • Review the logs on both the VM and the ESXi host to look for any errors or warnings related to network connectivity.
  • Check the DHCP server logs for any relevant information on the VM’s attempts to obtain an IP address.

9. Test with a Different VM:

  • Create a new VM and connect it to the same virtual switch to see if it can get an IP address. This will help determine if the issue is specific to the problematic VM or a more general network problem.

10. Check Physical Network:

  • If the VM is not getting an IP address on multiple ESXi hosts, check the physical network infrastructure, such as switches and routers, for any issues or misconfigurations.

Example Troubleshooting Steps:

1. Verify Network Adapter Configuration:

Example:

  • Log in to the vSphere Web Client or vSphere Client.
  • Select the VM in question, go to “Edit Settings,” and check the network adapter settings.
  • Ensure that the network adapter is connected to the correct virtual switch, and the “Connect at power on” option is enabled.

2. Check DHCP Server:

Example:

  • Verify that the DHCP server is operational and serving IP addresses to other devices on the same network.
  • Log in to the DHCP server and check its logs for any errors or issues related to IP assignment for the VM’s MAC address.

3. Check VLAN and Network Segmentation:

Example:

  • If VLANs are in use, ensure that the VM’s virtual network adapter is assigned to the correct VLAN.
  • Verify that the physical network switch ports and ESXi host’s virtual switch are correctly configured for VLAN tagging.

4. Check ESXi Networking Settings:

Example:

  • Log in to the ESXi host using the vSphere Web Client or vSphere Client.
  • Go to “Networking” and verify the configuration of virtual switches, port groups, and VMkernel adapters.
  • Ensure that the VM’s port group has the correct VLAN settings and security policies.

5. Verify MAC Address:

Example:

  • Ensure that there are no MAC address conflicts in the network.
  • Check the DHCP server logs for any indications of a MAC address conflict with the VM.

6. Restart VM and Network Services:

Example:

  • Try restarting the VM to see if it can acquire an IP address upon boot.
  • Restart the network services on the ESXi host using the command-line interface (CLI):
/etc/init.d/networking restart

7. Check Security Settings:

Example:

  • Review any firewall rules or security settings that might be affecting network communication for the VM.
  • Temporarily disable any restrictive firewall rules and see if the VM gets an IP address.

8. Check Logs:

Example:

  • Check the VM’s operating system logs for any network-related errors or warnings.
  • Review ESXi host logs, such as /var/log/vmkernel.log and /var/log/vpxa.log, for any relevant information.

9. Test with a Different VM:

Example:

  • Create a new VM and attach it to the same virtual switch to see if it can get an IP address. This helps determine if the issue is specific to the problematic VM or a more general network problem.

10. Check Physical Network:

Example:

  • If the issue persists across multiple ESXi hosts, check the physical network infrastructure, such as switches and routers, for any issues or misconfigurations.

Conclusion:

Troubleshooting a VM not getting an IP address on VMware ESXi involves checking various settings, configurations, and logs to identify the root cause of the problem. By following these example troubleshooting steps, you can isolate and resolve the issue, ensuring proper network connectivity for the affected VM.

Esxcli and vim-cmd commands for VM related queries

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esxcli is a powerful command-line tool in VMware ESXi that allows you to manage various aspects of your virtual machines (VMs). It provides a wide range of commands to query and configure VM-related settings. Below are some commonly used esxcli commands for VM-related queries, along with examples:

1. List Virtual Machines:

To view a list of all virtual machines registered on the ESXi host:

esxcli vm process list

2. Display VM Information:

To display detailed information about a specific virtual machine:

esxcli vm process list | grep -i "Display Name"

Replace "Display Name" with the name of the virtual machine you want to query.

3. Power Operations (Start, Stop, Restart):

To power on a virtual machine:

esxcli vm process start --vmid=<VMID>

Replace <VMID> with the VM’s unique identifier (you can get it from the output of the previous esxcli vm process list command).

To power off a virtual machine:

esxcli vm process kill --type=soft --world-id=<WORLD_ID>

Replace <WORLD_ID> with the VM’s World ID (you can find it in the output of the previous esxcli vm process list command).

4. Check VM Tools Status:

To check the VM Tools status for a virtual machine:

esxcli vm process list | grep -i "Tools"

This will show you whether VM Tools are running, not running, or not installed for each VM.

5. Check VM Resource Allocation:

To view the CPU and memory allocation for a specific virtual machine:

vim-cmd vmsvc/get.summary <VMID> | grep -E "vmx|memorySizeMb"

Replace <VMID> with the VM’s unique identifier.

6. Query VM vCPUs and Cores:

To check the number of virtual CPUs and cores per socket for a virtual machine:

vim-cmd vmsvc/get.config <VMID> | grep -E "numvcpus|coresPerSocket"

Replace <VMID> with the VM’s unique identifier.

7. Query VM Network Adapters:

To list the network adapters attached to a virtual machine:

vim-cmd vmsvc/get.networks <VMID>

Replace <VMID> with the VM’s unique identifier.

8. List VM Snapshots:

To view the snapshots for a specific virtual machine:

vim-cmd vmsvc/snapshot.get <VMID>

Replace <VMID> with the VM’s unique identifier.

9. Query VM Disk Information:

To check the virtual disks attached to a virtual machine:

vim-cmd vmsvc/device.disklist <VMID>

10. Get VM IP Address:

To get the IP address of a virtual machine (requires VMware Tools running in the VM):

vim-cmd vmsvc/get.guest <VMID> | grep -i "ipAddress"

Replace <VMID> with the VM’s unique identifier.

Conclusion:

Using esxcli commands, you can easily query and manage various aspects of virtual machines on your VMware ESXi host. These commands provide valuable information about VMs, their configurations, resource allocation, and power states, allowing you to efficiently manage your virtual environment.

Troubleshooting DNS related issues

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To validate DNS records in Active Directory (AD), you can use various tools and commands available in Windows Server. Below are some common methods to validate DNS records in an AD environment:

1. DNS Manager:

The DNS Manager console in Windows Server allows you to view and manage DNS records for your Active Directory domain. It provides a graphical interface to browse and validate DNS records.

  • Open “DNS Manager” from the “Administrative Tools” or “Server Manager” on your Windows Server.
  • Expand your AD domain in the console tree to view the DNS zones.
  • Navigate through the zones to validate specific DNS records, such as A records, CNAME records, and more.

2. nslookup Command:

The nslookup command is a powerful tool to query DNS records from the command prompt. You can use it to validate DNS records for specific hosts.

  • Open a Command Prompt on a Windows machine.
  • Type nslookup followed by the hostname you want to validate:
nslookup hostname.domain.co
  • Replace hostname.domain.com with the FQDN (Fully Qualified Domain Name) you want to check. The command will display the corresponding IP address and the DNS server used for the lookup.

3. PowerShell (Resolve-DnsName):

PowerShell provides the Resolve-DnsName cmdlet, which allows you to query DNS records programmatically.

  • Open PowerShell with administrative privileges.
  • Use the Resolve-DnsName cmdlet to validate DNS records:
Resolve-DnsName hostname.domain.com
  • Replace hostname.domain.com with the FQDN you want to validate. The cmdlet will display DNS record information, including the IP address.

4. Active Directory Users and Computers (ADUC):

The ADUC console also provides a way to view DNS records associated with AD objects, such as computers and servers.

  • Open “Active Directory Users and Computers” from the “Administrative Tools” or “Server Manager” on your Windows Server.
  • Ensure that the “Advanced Features” option is enabled (under “View” in the menu).
  • Right-click on an AD object (e.g., a computer) and select “Properties.”
  • Go to the “Attribute Editor” tab and look for attributes such as dnsHostName, servicePrincipalName, and dNSHostName. These attributes contain DNS-related information.

5. Active Directory Sites and Services:

The “Active Directory Sites and Services” console allows you to manage site and subnet information in AD. It also displays related DNS records.

  • Open “Active Directory Sites and Services” from the “Administrative Tools” or “Server Manager” on your Windows Server.
  • Expand the “Sites” node and browse through the site and subnet objects.
  • Right-click on a site or subnet object and select “Properties” to view DNS-related information.

Validation of forward and reverse DNS lookup is essential to ensure the accuracy and consistency of DNS records. Forward lookup (also known as DNS resolution) involves resolving a hostname to its corresponding IP address, while reverse lookup involves resolving an IP address to its associated hostname. Here are examples of how to perform forward and reverse DNS lookup and validate their results:

1. Forward DNS Lookup (Hostname to IP Address):

Example: Using nslookup Command

To perform a forward DNS lookup using the nslookup command in a command prompt or terminal:

nslookup www.example.com

Replace www.example.com with the hostname you want to resolve. The command will return the corresponding IP address for the hostname.

Example: Using PowerShell (Resolve-DnsName)

In PowerShell, you can use the Resolve-DnsName cmdlet for forward DNS lookup:

Resolve-DnsName www.example.com

Replace www.example.com with the hostname you want to resolve. The cmdlet will provide the corresponding IP address.

2. Reverse DNS Lookup (IP Address to Hostname):

Example: Using nslookup Command

To perform a reverse DNS lookup using the nslookup command, provide the IP address as an argument:

nslookup 192.168.1.1

Replace 192.168.1.1 with the IP address you want to reverse lookup. The command will return the associated hostname.

Example: Using PowerShell (Resolve-DnsName)

In PowerShell, you can use the Resolve-DnsName cmdlet for reverse DNS lookup by specifying the -Type PTR parameter:

Resolve-DnsName 192.168.1.1 -Type PTR

Replace 192.168.1.1 with the IP address you want to reverse lookup. The cmdlet will provide the associated hostname.

Validation of Forward and Reverse Lookup:

To validate the forward and reverse lookup results, ensure that the IP address obtained from forward lookup matches the original IP address used for reverse lookup, and vice versa. If there is a mismatch or if the lookup fails, it could indicate DNS configuration issues, such as missing or incorrect DNS records.

Example: Validation of Forward and Reverse Lookup

Suppose we have a forward lookup that returns the following:

Forward Lookup:
Hostname: www.example.com
IP Address: 203.0.113.10

Next, perform a reverse lookup on the IP address:

Reverse Lookup:
IP Address: 203.0.113.10
Hostname: server.example.com

To validate:

  1. The IP address obtained from the forward lookup (203.0.113.10) matches the IP address used for the reverse lookup (203.0.113.10).
  2. The hostname obtained from the reverse lookup (server.example.com) matches the hostname used for the forward lookup (www.example.com).

In Linux, validating DNS (Domain Name System) entries involves checking the correctness and consistency of DNS configurations on the local machine. The primary focus is on the /etc/hosts file for static DNS entries and the /etc/resolv.conf file for DNS resolver configuration. Additionally, you can use commands like nslookup and dig to test DNS resolution and verify DNS records. Here’s a step-by-step guide on how to validate DNS entries in Linux:

1. Check /etc/hosts file:

The /etc/hosts file is used for static DNS entries on the local machine. It maps hostnames to IP addresses. Ensure that the entries are correct and there are no duplicate or conflicting entries.

Example:

Open the /etc/hosts file using a text editor like nano or vi:

sudo nano /etc/hosts

Verify that the entries are in the following format:

IP_Address  Hostname  Alias1 Alias2 ...

Ensure that each entry has a unique IP address and hostname.

2. Verify /etc/resolv.conf file:

The /etc/resolv.conf file contains the DNS resolver configuration. It specifies the DNS servers that the system should use for DNS resolution.

Example:

Open the /etc/resolv.conf file using a text editor:

sudo nano /etc/resolv.conf

Ensure that it contains at least one valid nameserver entry pointing to a functional DNS server. For example:

nameserver 8.8.8.8

3. Test DNS Resolution using nslookup:

The nslookup command can be used to perform DNS queries and test DNS resolution for specific hostnames or IP addresses.

Example:

nslookup www.example.com

Replace www.example.com with the hostname you want to look up. The command should return the corresponding IP address and additional information, including the DNS server used for the resolution.

4. Test DNS Resolution using dig:

The dig (Domain Information Groper) command is another tool for DNS query and lookup. It provides detailed information about DNS records.

Example:

dig www.example.com

Replace www.example.com with the hostname you want to look up. The command will display various DNS records, including the IP address, TTL (Time to Live), authoritative name servers, and more.

5. Verify Reverse DNS (PTR) Records:

To validate reverse DNS (PTR) records, perform a reverse lookup of an IP address to check if it matches the expected hostname.

Example:

nslookup 203.0.113.10

Replace 203.0.113.10 with the IP address you want to reverse lookup. The command should return the associated hostname if the PTR record is correctly configured.

In Windows, there are several methods and tools available to validate DNS (Domain Name System) records and ensure proper name resolution. Below are some common ways to perform DNS validation from a Windows machine:

1. nslookup Command:

The nslookup command is a built-in Windows utility that allows you to query DNS records from the command prompt.

2. PowerShell (Resolve-DnsName):

PowerShell provides the Resolve-DnsName cmdlet, which allows you to query DNS records programmatically.

3. Network and Sharing Center:

The Network and Sharing Center in Windows allows you to view network connections and their associated DNS settings.

  • Right-click on the network icon in the system tray and select “Open Network & Internet settings.”
  • Click on “Change adapter options.”
  • Right-click on the network adapter and select “Status.”
  • Click on the “Details” button to view the DNS servers used by the network adapter.

4. Windows Event Viewer:

The Windows Event Viewer contains logs related to DNS events and errors. You can use it to monitor DNS-related activities and troubleshoot DNS issues.

  • Open Event Viewer on your Windows machine.
  • Navigate to “Windows Logs” > “System.”
  • Look for DNS-related events, such as DNS Client events and DNS Server events, which might provide information about DNS resolution and communication.

5. Windows Settings:

Windows Settings provide access to DNS-related configuration for the network adapter.

  • Open “Settings” on your Windows machine.
  • Go to “Network & Internet” > “Ethernet” (or “Wi-Fi,” depending on the connection type).
  • Click on the connected network adapter.
  • Scroll down and click on “Properties” to view and configure the DNS server addresses manually if necessary.

Network-related issues on an ESXi host

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When there are network-related issues on an ESXi host, it can impact the communication between the host, virtual machines, and other network resources. To troubleshoot network issues on ESXi, there are several logs to check. Additionally, if the ESXi host is connected to a physical switch, it’s essential to examine the switch logs as well. Below are the logs to check for ESXi network issues, along with examples:

Logs to Check on ESXi Host:

  1. vmkernel.log: This log records ESXi kernel messages, including networking-related events and errors.
  2. messages.log: This log contains system messages, including network-related information.
  3. vmkwarning.log: This log records various warnings, including networking warnings.
  4. net-dvs.log: This log pertains to the Distributed Virtual Switch (DVS) and contains events related to virtual networking.
  5. hostd.log: While primarily used for host management events, this log may contain information related to network configuration changes or errors.

Examples of Network Issues in ESXi Logs:

Example 1: Network Connectivity Issue in vmkernel.log:

2023-07-01T12:34:56.789Z cpu1:12345)vmnicX: Link Up event. MAC Address: xx:xx:xx:xx:xx:xx
2023-07-01T12:34:57.123Z cpu2:12346)vmnicX: Link Down event.

In this example, the log shows a network interface (vmnicX) experiencing a link-up event followed by a link-down event, indicating a potential connectivity problem.

Example 2: Duplicate IP Address Detected in vmkwarning.log:

2023-07-01T12:34:56.789Z cpu1:12345)WARNING: VmknicIpRouteAddVmknicVmk0:Netstack Register Route(Vmknic) failed, Error 17099 (No IP Address: xx.xx.xx.xx) on dvPort 12345:Uplink(vmnicX)/0. Action Required: Verify IP Address on Vmknic vmk0.

This log entry indicates that a duplicate IP address has been detected on the vmk0 interface, which may lead to connectivity issues.

Logs to Check on the Physical Switch:

The logs on the physical switch connected to the ESXi host can provide valuable information about network events and errors.

Examples of Switch Logs:

Example 3: Port Flapping in Switch Logs:

2023-07-01T12:34:56.789Z: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/1, changed state to down
2023-07-01T12:34:57.123Z: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/1, changed state to up

These log entries indicate that the physical switch port GigabitEthernet1/0/1 experienced a link down event followed by a link up event, which may cause network interruptions.

Example 4: Switch Port Errors:

2023-07-01T12:34:56.789Z: %ERR-3-IF_DOWN_LINK_FAILURE: Interface GigabitEthernet1/0/1 is down (Link failure)

This log entry suggests that the switch port GigabitEthernet1/0/1 is down due to a link failure.

Conclusion:

When troubleshooting network-related issues on an ESXi host, it’s crucial to check the ESXi logs, such as vmkernel.log, messages.log, and others. These logs can provide insights into network events, warnings, and errors. Additionally, if the ESXi host is connected to a physical switch, examining the switch logs can be equally important in identifying potential switch-related problems. Analyzing the logs and resolving network issues promptly will help ensure the stability and performance of the ESXi host and its virtual machines.

LUN (Logical Unit Number) is disconnected from ESXi host what do we check ?

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When a LUN (Logical Unit Number) is disconnected from an ESXi host, it can result in data access issues and VM disruptions. To troubleshoot and resolve the LUN disconnection, you need to check both the ESXi host and the storage side to identify the cause of the disconnection. Below are the steps to check from both ESXi and storage perspectives:

Checking from ESXi Host:

1:Review Storage Adapters: Check if the storage adapter(s) on the ESXi host are detecting the LUN properly. Use the following command to list the storage adapters:

esxcli storage core adapter list

Verify that the adapter that connects to the storage where the LUN is located is active and working without any errors.

2:Check Storage Devices: Ensure that the storage devices are visible and accessible. Use the following command to list the storage devices:

esxcli storage core device list

Verify that the device corresponding to the LUN is present and not showing any errors.

3:Check LUN Configuration: Verify the LUN configuration on the ESXi host. Use the following command to list the mounted VMFS datastores:

esxcli storage filesystem list

Ensure that the LUN’s VMFS datastore is listed and mounted correctly.

4:Check Path Status: Verify the path status to the LUN. Use the following command to list the storage paths:

esxcli storage core path list

Ensure that all paths to the LUN are active and showing the “Normal” state.

5:Rescan Storage: If the LUN was recently connected or disconnected, perform a storage rescan on the ESXi host to refresh the storage information:

esxcli storage core adapter rescan --all
  1. Check Logs: Review the ESXi logs (e.g., vmkernel.log, messages.log) for any storage-related errors or warnings around the time of the LUN disconnection. Use commands like tail or cat to view the logs.

Checking from Storage:

  1. Storage Array Management: Log in to the storage array management interface or storage management software to check the status of the LUN. Look for any errors, warnings, or status indicators related to the LUN.
  2. LUN Visibility: Ensure that the storage array is detecting the LUN and making it available to the ESXi host. Verify that the LUN is properly presented to the correct ESXi host(s).
  3. Check for Errors: Look for any specific errors or alerts related to the LUN or the storage array that may indicate a problem.
  4. Check Connectivity: Verify the connectivity between the storage array and the ESXi host(s) by checking the network connectivity, Fibre Channel (FC) or iSCSI connections, and any relevant zoning or masking configurations.
  5. Check Disk Health: Review the disk health status of the physical disks associated with the LUN. Ensure there are no reported issues with the disks.

To troubleshoot a LUN disconnection, it is essential to check the logs on the ESXi host. The primary logs to review for LUN disconnection issues are the vmkernel.log and messages.log files. Below are the steps to check these logs along with examples:

Step 1: SSH to ESXi Host:

Enable SSH on the ESXi host and use an SSH client (e.g., PuTTY) to connect to the host.

Step 2: View vmkernel.log:

Use the following command to view the last 100 lines of the vmkernel.log file:

tail -n 100 /var/log/vmkernel.log

Example 1: SCSI Errors in vmkernel.log:

If there is a LUN disconnection, you might see SCSI errors in the vmkernel.log. These errors could indicate issues with the storage device or communication problems.

2023-07-01T12:34:56.789Z cpu1:12345)ScsiDeviceIO: XXXX: Device  naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx performance has deteriorated. I/O latency increased from average value of X microseconds to Y microseconds.

Example 2: LUN Disconnection in vmkernel.log:

A LUN disconnection event can be logged in the vmkernel.log as well.

2023-07-01T12:34:56.789Z cpu1:12345)NMP: nmp_DeviceConnect:3779: Successfully opened device naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.
2023-07-01T12:34:56.790Z cpu2:12346)NMP: nmp_DeviceDisconnect:3740: Disconnect device "naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" due to LUN Reset event. I/O error status: [Aborted].

Step 3: View messages.log:

Use the following command to view the last 100 lines of the messages.log file:

tail -n 100 /var/log/messages.log

Example 3: Multipath Errors in messages.log:

If there are multipath-related issues, you might see errors in the messages.log.

2023-07-01T12:34:56.789Z cpu1:12345)WARNING: NMP: nmpDeviceAttemptFailover:512: Retry world failover device "naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" - issuing command X.

Example 4: LUN Disconnection in messages.log:

A LUN disconnection event might be logged in the messages.log as well.

2023-07-01T12:34:56.789Z cpu2:12346)WARNING: NMP: nmpDeviceBadLink:7152: NMP: nmp_DeviceStartLoop:984: NMP Device "naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" loop reset with I/O error.

By checking the vmkernel.log and messages.log files on the ESXi host, you can gather valuable information about LUN disconnection events and any related errors or warnings. This information is essential for diagnosing the cause of the LUN disconnection and taking appropriate corrective actions to restore normal operations. If needed, involve storage and VMware support teams to assist with the troubleshooting process.