Labels

Wednesday, July 1, 2009

PowerShell - vSphere VMKernel NIC MTU

I came across a problem with VI4 (vSphere) on ESXi, where I was unable to create a vmkernel NIC for iSCSI with the vicfg-vmknic.pl script to set a custom MTU of 9000. This post provides a method using the GUI/perl script, and a PowerShell vSphere PowerCLI script to modify an existing VMKernel NIC.

It seems there is a bug in the perl script doesn't allow you to create a VMKernel NIC, however it does work if you create one through the GUI, and then use the script to delete and re-create the virtual NIC.

This was using a standalone ESXi server with a normal vSwitch - it wasn't managed by VC and it wasn't a DVS.

The GUI/PL script method:

  1. Create a VMKernel NIC in an existing vSwitch through the VI Client, with a port group called iSCSI1 in this example.
  2. Using the CLI, run the following commands, the first to delete the existing NIC, and then another to re-create the same NIC, but with an increased MTU:
    vicfg-vmknic.pl -d iSCSI1
    vicfg-vmknic.pl -a -i x.x.x.x -n x.x.x.x -m 9000 iSCSI1
  3. Run 'vicfg-vmknic.pl –l' to list the VMK NICs, which should show the adjusted MTU

I wasn't particularly happy with this method, so I looked at using the vSphere PowerCLI to set the MTU. For whatever reason, VMware chose not to expose the MTU property, which leaves only the SDK.

Luckily the PowerCLI makes it much easier to use the .Net SDK than previously possible with the Get-View cmdlet, so the script below is a combination of standard PowerCLI with a hook into the vNIC collection and the UpdateVirtualNic method to change a virtual NIC spec.


param (

    $MTU = 9000, 
    $nicName = vmk1, 
    $vcServer = "vcServer", 
    $vmServerName = "esx01"
)

#
#
# Description:
#  Update the MTU of a vmkernel NIC used for iSCSI
#
# Limitations:
#  DVS untested
#
# Assumptions, this script works on the assumption that:
#  The caller provides credentials with permissions to change the specified NIC
#
# Arguments:
#  MTU, The new MTU size, eg. 9000
#  nicName, The vmkernel NIC, eg. vmk1.  Note that this differs from the port group (eg. iSCSI1, with a NIC name of vmk1)
#  vcServer, the VC instance to connect to, eg. vcServer
#  vmServerName, The server name controlled by the VC instance (or direct), eg. esx01
#
# Usage:
#  PowerShell . .\UpdateVMKMTU.ps1 -MTU 9000 -nicName 'vmk1' -vcServer 'vcServer' -vmServerName 'esx01'
#
# References:
#  http://www.vmware.com/support/developer/vc-sdk/visdk400pubs/ReferenceGuide/vim.host.VirtualNic.Specification.html
#
# Changes:
#  26/06/2009, Wayne Martin, initial version

#$ErrorActionPreference = "Continue"


Connect-VIServer -server $vcServer        # connect to VC
$hostSystem = get-view -ViewType HostSystem -Filter @{"Name" = $vmServerName}   # Find the .Net view of the specified host
$hostConfigManager = $hostSystem.get_ConfigManager()      # Get the config manager
$hostNetworkSystem = $hostConfigManager.get_NetworkSystem()     # Find the MOR of the host network system
$netSystem = Get-View $hostNetworkSystem       # Get the object from the reference for the update method later

$hostconfig = $hostSystem.Config        # Get the current host config
$hostNetwork = $hostconfig.Network        # Get the current network host config
$hostvNIC = $hostNetwork.vNic         # Get the virtual NICs

$nicBeingUpdated = $null
foreach ($hostVirtualNIC in $hostvNIC) {       # For each virtual NIC
    if ($hostVirtualNIC.Device -eq $nicName) {        # Is this the device specified?
        $nicBeingUpdated = $hostVirtualNIC       # Yes, copy the object
    }
}

if ($nicBeingUpdated) {          # Was something found?
    $nicSpec = $nicBeingUpdated.Spec        # Yes, get the current spec
    $currentMTU = $nicSpec.MTU         # Get the current MTU from the spec

    if ($currentMTU -ne $MTU) {         # Is the MTU different?
        $nicSpec.set_Mtu($MTU)         # Yes, update the MTU on the copy of the spec of the existing NIC
        $netSystem.UpdateVirtualNic($nicName, $nicSpec)             # Call the update method from the netsystem, to update the NIC with the modified device spec

        write-output "MTU for $nicName updated from $currentMTU to $MTU"
        (get-vmhostnetwork).VirtualNic        # Output updated information
    } else {
        write-output "MTU for $nicName already set to $MTU, no changes made"
    }

} else {

    write-output "NIC $nicName not found, no changes made"

}


Wayne's World of IT (WWoIT), Copyright 2009 Wayne Martin. 

2 comments:

Unknown said...

Thanks for that scirpt. It saved me a bunch of time.

When I cut and pasted your script, I did run into one bug. Line 64:

(get-vmhostnetwork).VirtualNic # Output updated information

had to be changed to:

(get-vmhostnetwork -VMhost $vmServerName).VirtualNic # Output updated information

The error from a straight cut and past from your published scirpt is shown below.

MTU for vmk2 updated from 1500 to 9000
Get-VMHostNetwork : Value cannot be found for the mandatory parameter VMHost
At C:\Program Files\VMware\Infrastructure\vSphere PowerCLI\Scripts\UpdateVMKMTU.ps1:64 char:27

Anders Olsson said...

Hi. Thanks for the tip. This is a very handy script, since the built-in Perl scripts don't allow changing the MTU without deleting and re-creating the entire vmknic. This is particularly difficult when changing MTU for the VMkernel Management port, since it's the one you are actually connecting to when executing the script.

However, the script on the page doesn't seem to work. The output says "MTU for vmk0 updated from 1500 to 9000", but the setting never actually sticks. Rebooting the ESX server didn't help.

Any ideas?


All Posts

printQueue AD objects for 2003 ClusterVirtualCenter Physical to VirtualVirtual 2003 MSCS Cluster in ESX VI3
Finding duplicate DNS recordsCommand-line automation – Echo and macrosCommand-line automation – set
Command-line automation - errorlevels and ifCommand-line automation - find and findstrBuilding blocks of command-line automation - FOR
Useful PowerShell command-line operationsMSCS 2003 Cluster Virtual Server ComponentsServer-side process for simple file access
OpsMgr 2007 performance script - VMware datastores...Enumerating URLs in Internet ExplorerNTLM Trusts between 2003 and NT4
2003 Servers with Hibernation enabledReading Shortcuts with PowerShell and VBSModifying DLL Resources
Automatically mapping printersSimple string encryption with PowerShellUseful NTFS and security command-line operations
Useful Windows Printer command-line operationsUseful Windows MSCS Cluster command-line operation...Useful VMware ESX and VC command-line operations
Useful general command-line operationsUseful DNS, DHCP and WINS command-line operationsUseful Active Directory command-line operations
Useful command-linesCreating secedit templates with PowerShellFixing Permissions with NTFS intra-volume moves
Converting filetime with vbs and PowerShellDifference between bat and cmdReplica Domain for Authentication
Troubleshooting Windows PrintingRenaming a user account in ADOpsMgr 2007 Reports - Sorting, Filtering, Charting...
WMIC XSL CSV output formattingEnumerating File Server ResourcesWMIC Custom Alias and Format
AD site discoveryPassing Parameters between OpsMgr and SSRSAnalyzing Windows Kernel Dumps
Process list with command-line argumentsOpsMgr 2007 Customized Reporting - SQL QueriesPreventing accidental NTFS data moves
FSRM and NTFS Quotas in 2003 R2PowerShell Deleting NTFS Alternate Data StreamsNTFS links - reparse, symbolic, hard, junction
IE Warnings when files are executedPowerShell Low-level keyboard hookCross-forest authentication and GP processing
Deleting Invalid SMS 2003 Distribution PointsCross-forest authentication and site synchronizati...Determining AD attribute replication
AD Security vs Distribution GroupsTroubleshooting cross-forest trust secure channels...RIS cross-domain access
Large SMS Web Reports return Error 500Troubleshooting SMS 2003 MP and SLPRemotely determine physical memory
VMware SDK with PowershellSpinning Excel Pie ChartPoke-Info PowerShell script
Reading web content with PowerShellAutomated Cluster File Security and PurgingManaging printers at the command-line
File System Filters and minifiltersOpsMgr 2007 SSRS Reports using SQL 2005 XMLAccess Based Enumeration in 2003 and MSCS
Find VM snapshots in ESX/VCComparing MSCS/VMware/DFS File & PrintModifying Exchange mailbox permissions
Nested 'for /f' catch-allPowerShell FindFirstFileW bypassing MAX_PATHRunning PowerSell Scripts from ASP.Net
Binary <-> Hex String files with PowershellOpsMgr 2007 Current Performance InstancesImpersonating a user without passwords
Running a process in the secure winlogon desktopShadow an XP Terminal Services sessionFind where a user is logged on from
Active Directory _msdcs DNS zonesUnlocking XP/2003 without passwords2003 Cluster-enabled scheduled tasks
Purging aged files from the filesystemFinding customised ADM templates in ADDomain local security groups for cross-forest secu...
Account Management eventlog auditingVMware cluster/Virtual Center StatisticsRunning scheduled tasks as a non-administrator
Audit Windows 2003 print server usageActive Directory DiagnosticsViewing NTFS information with nfi and diskedit
Performance Tuning for 2003 File ServersChecking ESX/VC VMs for snapshotsShowing non-persistent devices in device manager
Implementing an MSCS 2003 server clusterFinding users on a subnetWMI filter for subnet filtered Group Policy
Testing DNS records for scavengingRefreshing Computer Account AD Group MembershipTesting Network Ports from Windows
Using Recovery Console with RISPAE Boot.ini Switch for DEP or 4GB+ memoryUsing 32-bit COM objects on x64 platforms
Active Directory Organizational Unit (OU) DesignTroubleshooting computer accounts in an Active Dir...260+ character MAX_PATH limitations in filenames
Create or modify a security template for NTFS perm...Find where a user is connecting from through WMISDDL syntax in secedit security templates

About Me

I’ve worked in IT for over 20 years, and I know just about enough to realise that I don’t know very much.