Details
To account for overheads such as physical NIC ports (uplinks), CDP traffic, and network discovery, ESX 3.x, ESX/ESXi3.5.x, and ESX/ESXi 4.x allocate and reserve an additional eight ports per virtual switch beyond what is available for virtual machine use. This additional overhead is allocated regardless of the number of ports on the virtual switch, and accounts for the most common product deployment scenarios.
Solution
Configuring a virtual switch from vSphere Client
When configuring a virtual switch from vSphere Client, the ESX machine provides available virtual switch port count, which already reflects the fixed overhead (8, 24, 56, 120, 248, 504, 1016, 2040, and 4088 available ports respectively).
Note: Only ESX/ESXi 4.x have 2040 or 4088 ports.
Configuring a virtual switch using esxcfg-vswitch command
When configuring a virtual switch using esxcfg-vswitch command, this overhead must be explicitly taken into account when specifying the total number of ports to allocate. Available port counts as displayed in vSphere Client need to be incremented by eight when working with esxcfg-vswitch command.
| vSphere Client | esxcfg-vswitch | Total Ports |
| 8 | 16 | 8 virtual machine + 8 Reserved |
| 24 | 32 | 24 virtual machine + 8 Reserved |
| 56* | 64 | 56 virtual machine + 8 Reserved |
| 120** | 128 | 120 virtual machine + 8 Reserved |
| 248 | 256 | 248 virtual machine + 8 Reserved |
| 504 | 512 | 504 virtual machine + 8 Reserved |
| 1016 | 1024 | 1016 virtual machine + 8 Reserved |
| 2040*** | 2048 | 2040 virtual machine + 8 Reserved |
| 4088*** | 4096 | 4088 virtual machine + 8 Reserved |
* = System default for new virtual switches in ESX/ ESXi 3.x
** = System default for new virtual switches in ESX/ ESXi 4.x
*** = Only for ESX/ESXi 4.0
Note: Certain higher-complexity product deployment scenarios might require more eight virtual switch ports for overhead.
Typically, each additional uplink connected to the same virtual switch beyond the first six uplinks reduces the number of ports available on that virtual switch for virtual machine use by one.
Deployment scenarios where a very large number of uplinks are teamed together on a single virtual switch might significantly impact the number of ports on that virtual switch available for virtual machine use, and the overall size of the virtual switch might need to be adjusted accordingly.
The current port utilization data for virtual switches can be reviewed by using the esxcfg-vswitch --list command.
The current overhead utilization on a given virtual switch can be calculated by subtracting the Used Ports value for all PortGroups from the Used Ports value for that virtual switch.
Typically, each additional uplink connected to the same virtual switch beyond the first six uplinks reduces the number of ports available on that virtual switch for virtual machine use by one.
Deployment scenarios where a very large number of uplinks are teamed together on a single virtual switch might significantly impact the number of ports on that virtual switch available for virtual machine use, and the overall size of the virtual switch might need to be adjusted accordingly.
The current port utilization data for virtual switches can be reviewed by using the esxcfg-vswitch --list command.
The current overhead utilization on a given virtual switch can be calculated by subtracting the Used Ports value for all PortGroups from the Used Ports value for that virtual switch.
Source:-
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1008040
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