Deep Dive: Virtual Switch Security settings and Port Binding

Security Settings:

Three options are available on a virtual switch.  These settings can be set at the switch layer then overwritten on individual port groups.

  • Promiscuous Mode – This allows the guest adapter to detect all frames passed on the vSwitch that are in the same VLAN as the guest.  Allows for packet sniffing.  This is not port mirroring it only allows a host to see it’s own traffic and any broadcast traffic.
  • MAC Address Change – Allows the guest to change it’s mac address.  If set to reject all frames for the mac not in the .vmx file are dropped at the switch.
  • Forged Transmits – If set to reject all frames from the guest with a mac address that does not match the .vmx file are dropped.

Security settings advise:

Set all three to reject on the switch keeping your operating systems admins in a box while protecting shared resources.   Then add individual polices to each port group as needed.   If you are wondering where it’s needed one of the use cases is nested virtualization.. which requires all three to be set to accept.

Port Binding:

Port binding is a setting that allows you to determine how and when the ports on a virtual switch are allocated.  Currently there are three port binding options:

  • Static binding (default)
  • Dynamic binding
  • Ephemeral binding

Static Binding – means a port is allocated to a virtual machine when it is added to the port group.  Once allocated to the port group it continues to use the port until removed from the port group (via deletion or move to another port group).  Network stats with static binding is kept through power off and vMotion.

Dynamic Binding – will be removed in the near future. Ports are allocated only when a virtual machine is powered on and the virtual network card is connected.  They are dynamically allocated when needed.  Network stats are kept through vMotion but not power off.

Ephemeral Binding – Is a lot like a standard vSwitch it can be managed from the vCenter or ESXi host.  Ports are allocated when the host is powered on and nic is connected.  One major difference is that dvPorts are created on demand all other binding type creates them when the port group is created.  This process takes more RAM and processor power and so their are limits on the number of ephemeral ports available.  Ephemeral ports are used for recovery when vCenter is down and may help with vCenter availability.  All stats are lost when you vMotion or power off the virtual machine.

Port Group Type advice:

I would use static binding on almost everything.  Ephemeral has a high cost and does not scale.  I do personally use ephemeral for vCenter because I use 100% dVS switches.  If you are using standard switches just use static across the board.


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