VMKPING and its uses in ESXI

I have recently been working with esxi hosts and to decommission them and recommission them into new projects and had to use the command vmkping to test the MTU of certain types of vmkernel ports like VMOTION, VSAN, VTEPs etc.

Here is a refresher for the vmkping commands which are very useful for a day to day Virtual Administrator

Command to check the MTU of 9000 with a certain amount of packets and with a certain interval and using a certain vmkernel port

vmkping -I vmk3 -d -s 8972 -c 1000 -i 0.005

vmkping -d -s 1472 <IP_Address>

In one of the above command vmkernel port is vmk3, for MTU 9000, we will be using 8972 as the packet size , -c is the count of packets and -i is the interval for which the ping will work (In the above example it is 0.005 seconds)

The second command is to test the MTU 1500 and the IP to test. You can also add -I (Interface) and vmkernel port through which you want to ping the IP

Command to check the communication of an IP address through an vmkernel port

vmkping -I vmk# IP address of the host

Command to get all the network adapters and the type of tcp/ip stack assigned to the nics

esxcfg-vmknic -l

Using the above command you can check the netstack which will be used in the below command to ping a vmotion vmkernel port

vmkping -S vmotion -I vmk1 <IP_Address_to_ping>

The -S is for netstack name like vmotion and this is the only command to be used if we use a NetStack

List of arguments:

vmkping [args] [host/IP_Address]


  -4                            use IPv4 (default)

  -6                            use IPv6

  -c <count>            set packet count

  -d                           set DF bit (IPv4) or disable fragmentation (IPv6)

  -D                           vmkernel TCP stack debug mode

  -i <interval>           set interval (secs)

  -I <interface>         outgoing interface – for IPv6 scope or IPv4 bypasses routing lookup

  -N <next_hop>       set IP*_NEXTHOP – bypasses routing lookup

                                  for IPv4, -I option is required

  -s <size>                 set the number of ICMP data bytes to be sent.

                                  The default is 56, which translates to a 64 byte

                                  ICMP frame when added to the 8 byte ICMP header.

                                 (Note: these sizes does not include the IP header).

  -t <ttl>                   set IPv4 Time To Live or IPv6 Hop Limit

  -v                            verbose

  -W <timeout>        set timeout to wait if no responses are received (secs)

  -X                            XML output format for esxcli framework.

  -S                           The network stack instance name. If unspecified the default netstack instance is used.

Disable vSphere Managed Object Browser (MOB)

To harden your ESXi 6.0 hosts, we disable the MOB service so that any attacker can’t get to the web browser and access the MOB of the ESXi host (ex: https://esxi01.lab.com/mob), this setting will disable one of the attack vectors of theESXi hosts in the environment.

to do this, you SSH into the ESXi host where you want to disable the mob service and perform the following commands

esxi01# vim-cmd proxysvc/remove_service "/mob" "httpsWithRedirect"

to verify if the mob service has been removed from the ESXi host, use the following command

esxi01# vim-cmd proxysvc/service_list

the above command will list all the services on the ESXi host, look for the service “/mob”, if you don’t see this service, then it has been removed. if it is still there, then you will have to perform the first command and reboot the ESXi host to disable the mob service from the host.



Can’t fork error on ESi 6 host on UCS Blade

Recently, I was working on an UCS blade firmware upgrade along with esxi upgrade from esxi 5.5 to 6.0 and came across this error where the esxi host became unresponsive with an error “can’t fork” on its DCUI.

here is a little background on this story, this particular blade was B240 blade which was being used as SAP HANA blade by the customer and the firmware upgrade and esxi upgrade went fine and two days later the host became unresponsive and we couldn’t connect to it using SSH, DCUI, etc, connecting to the kvm console revealed the below screen when we went to its Alt+F1 command interface


we had to bounce the box and we had to reduce the linux vm memory which was hosting SAP HANA on it to be 10% less than the memory of the esxi host.

Conclusion: The HANA VM (linux) on the esxi host should have 10% less memory than the overall memory of the esxi host to avoid this problem.

How to Install Cisco VEM vib on an ESXi 6 host

Recently, I had to install the Cisco vem module onto an esxi 6 host as it was not installed and i couldn’t join the esxi host to the cisco nexus 1000v distributed switch. here is the process on how to first check if the vem module is installed on the esxi host.

SSH into the esxi host and run the following commands to check if the VEM module is installed

host# esxcli software vib list | grep -i vem

the above command will display the cisco vem module installed on the esxi host, if nothing is displayed then you will have to install the vem module by downloading the vem vib from the nexus 1kv in the environment.

i did it by going to https://nexus1kv_hostname    in a web browser which will display you the vibs which you can download from nexus 1000v, download the vem vib associated with your environment and run the following command to install the vib onto the esxi host

upload the vem vib file onto a datastore on the host

SSH into the esxi host where you want to install the vem module

host# esxcli software vib install -v /vmfs/volumes/<directory_path>/cross_cisco-vem-version_x.x.x.x.x.vib

NOTE: directory_path in the above command is the place where the cisco vem vib is stored. (name of the datastore/volume)

Once the vib is installed you can check the status of the vem by using the command

host# vem status

The above command will display that the VEM agent (vemdpa) is running