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Enable Jumbo Frames in ESXi on a vmknic within a vNetwork Distributed Switch

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Justin C
AWS solutions and security architect with a strong background in VMware and security compliance.
To date, the MTU setting is not exposed via the GUI when creating a vmknic, and you cannot directly add a vmknic to a dvSwitch via the command line, so a workaround is needed. Keep in mind that for jumbo frames to be effective it must be enabled end-to-end, meaning that your vmknic, vSwitch, physical switch, and SAN must all be configured the same.  Here’s how I do it on ESXi 4.1 using vMA.

What you will need:
-vMA (free download from VMware)

First, install vMA:
1. Using the vSphere Client, connect to the vCenter server.
2. Right-click any host and select File > Deploy OVF Template.
3. In the wizard, select Deploy from file.
4. Click Browse, select the OVF and click Next.
5. Click Next when the download details are displayed.
6. Accept the license agreement.
7. Specify the name of the virtual machine.
8. Select the location for the VM.
9. Select the resource pool, if applicable.
10. Select the datastore for the VM.
11. Select the network mapping. We will select the dvPort Group associated with your Management Network so the vMA VM will have network access to the Management connections of your ESXi hosts.
12. Review the information and click Finish.

Now, configure it:
1. In the vSphere Client, right-click the virtual machine, and click Power On.
2. Select the Console tab.
3. Answer the network configuration prompts. You will need to enter valid networking information for the network your ESXi host reside on.
4. When prompted, specify a password for the vi-admin user. This must be a secure pass-word or you will see “Bad Password” displayed.
5. Log in using the vi-admin user and the newly configured password.
6. Type “vifp addserver ” where is the FQDN of the first ESXi host. You will be prompted for the ESXi host’s root password.
7. Verify that the server has been added to the FastPass server list, “vifp listservers”.
8. Repeat for all ESXi hosts to be managed.

Create the vmknic with an MTU size of 9000:
1. Log in using the vi-admin account and password.
2. Select the first ESXi host as the target using “vifptarget –s ”.
3. Create a local standard vSwitch on the ESXi host with no uplinks attached using “esxcfg-vswitch –a temp”. This will create a vSwitch named “temp”.
4. Create a port group named Storage on the test vSwitch using “esxcfg-vswitch –A Storage temp”
5. Create a vmknic with an MTU size of 9000 on the test vSwitch in port group Storage, “esxcfg-vmknic –a –i x.x.x.x –n –m 9000 –p Storage”, replace the x.x.x.x IP address in the example with the correct IP for your environment’s storage subnet.
6. Verify that the vmknic just created has an MTU size of 9000, “esxcfg-vmknic –l”, the newly created vmknic should be listed as “vmk1”, assuming you only had a single vmknic to begin with. Otherwise, adjust accordingly.
7. Repeat steps 2 through 6 for all ESXi hosts in your environment.

Now, migrate the vmknic(s) to the dvSwitch:
1. Log in to the vSphere Client and browse to Home > Inventory > Networking.
2. Expand the vCenter server name, datacenter name, and select the dvSwitch created pre-viously.
3. Right-click the dvSwitch and select Manage Hosts.
4. Select all ESXi hosts and click Next.
5. Expand each ESXi host and ensure the correct vmnics are assigned.
6. Click Next.
7. For each ESXi host you will see vmk0 and vmk1, assuming you have an existing Management Network connection (you wouldn’t be at this point if you didn’t). Under the Switch column, you will see that vmk1 is on the ‘test’ vSwitch that was created above.
8. Highlight vmk1 for the first ESXi host and click the Assign port group… button.
9. Highlight the dvPortGroup_your_storage_network dvPort Group and click OK.
10. Repeat steps 7 through 9 for each ESXi host.
11. Click Next.
12. Click Next at the Virtual machine networking page.
13. Click Finish.

The last step... change the MTU size for the dvSwitch:

1. Log in to the vSphere Client and browse to Home > Inventory > Networking.
2. Right-click the appropriate Distributed vSwitch and select Edit Settings.
3. On the Properties tab, click Advanced.
4. Set the Maximum MTU: to 9000.
5. Click OK.

Again, ensure that your physical switch and SAN are also configured to accept jumbo frames.  

Hope that helps!
Author:Justin C

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