How to Configure Jumbo Frames for an iSCSI Port Group – ESXi 4.1


If you want to enable jumbo frames on an iSCSI port group in ESXi 4.1, you’ll need to make configuration changes at the vSwitch and VMkernel NIC level.  Through trial and error, I found that I had to create the iSCSI port group from the command line instead of just enabling jumbo frames on an already existing port group.  At first, I already had an iSCSI port group created.  I did this via the vSphere Client.  But then enabling jumbo frames from the CLI didn’t work.  I had to delete the iSCSI port group first, then recreate from the CLI.  Note that these commands are case sensitive, including the names of vSwitches, port groups, and VMkernel NICs. These command were completed via an SSH session directly to an ESXi 4.1 host.

One other note is that I had to complete these commands one at a time.  I tried, for example, creating the vSwitch and adding the port group along with specifying a VLAN all at the same time.  Of course, it failed and a message told me I had to complete one at a time.

Enable jumbo frames on the vSwitch
esxcfg-vswitch –m 9000 vSwitch_Name

The -m sets the maximum transmission unit, MTU, size.

Example: esxcfg-vswitch -m 9000 vSwitch1

Create an iSCSI port group
esxcfg-vswitch –A iSCSI_Port_Group_Name vSwitch_Name

The -A is case sensitive and adds a port group to the designated vSwitch.

Example: esxcfg-vswitch -A iSCSI_1 vSwitch1

Add iSCSI VLAN to iSCSI port group
esxcfg-vswtich –p iSCSI_Portgroup_Name –v VLAN_Number vSwitch_Name

The -p specifies the port group on which you’re operating.  The -v adds a VLAN by VLAN number.

Example: esxcfg-vswitch -p iSCSI_1 -v 100 vSwitch1

Add VMkernel NIC to iSCSI portgroup
esxcfg-vmknic –a –i ip_address –n netmask –m 9000 iSCSI_Portgroup_Name

The -a is again case sensitive and means that you’re adding a VMkernel NIC.  The -i means you’re specifying an IP address, -n a subnet mask, and again the -m specifies MTU size.

Example: esxcfg-vmknic -a -i 192.168.1.100 -n 255.255.255.0 -m 9000 iSCSI_1

Verify vSwitch has jumbo frames enabled
esxcfg-vswitch –l

The -l is a lowercase L, for list, just like Linux.  Sample output from the list command is shown below.  Note the 9000 MTU size.

Switch Name Num Ports Used Ports Configured Ports MTU  Uplinks
vSwitch0              128              5               128            1500  vmnic1,vmnic2

PortGroup Name       VLAN ID Used Ports  Uplinks
vMotion                         12          1                  vmnic2,vmnic1
Management Network    13          1                 vmnic1,vmnic2

Switch Name Num Ports Used Ports Configured Ports MTU  Uplinks
vSwitch1            128            8                      128            9000     vmnic4,vmnic5

PortGroup Name  VLAN ID Used Ports Uplinks
VM Network               10              2           vmnic4,vmnic5
iSCSI_1                    100             1           vmnic4,vmnic5

Verify VMkernel NIC has jumbo frames enabled
esxcfg-vmknic –l

Again, the -l is a lowercase L.  Sample output is below.  Ensure you see 9000 for MTU size.

Interface Port Group/DVPort IP Family IP Address Netmask Broadcast MAC Address MTU TSO MSS Enabled Type
vmk0 Mgmt Network IPv4 xx.xx.xx.xx 255.255.255.0 xx.xx.xx.xx yy:yy:yy:yy:yy:yy 1500 65535 true STATIC
vmk1 vMotion IPv4 xx.xx.xx.xx 255.255.255.224 xx.xx.xx.xx yy:yy:yy:yy:yy:yy     1500 65535 true STATIC
vmk2 iSCSI_1 IPv4 xx.xx.xx.xx 255.255.255.224 xx.xx.xx.xxyy:yy:yy:yy:yy:yy 9000 65535 true STATIC

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