Following general network security recommendations is the first step in securing your networking environment. You can then move on to special areas, such as securing the network with firewalls or using IPsec.

  • Spanning Tree Protocol (STP) detects and prevents loops from forming in the network topology. VMware virtual switches prevent loops in other ways, but do not support STP directly. When network topology changes occur, some time is required (30–50 seconds) while the network relearns the topology. During that time, no traffic is allowed to pass. To avoid these problems, network vendors have created features to enable switch ports to continue forwarding traffic. For more information, see the VMware knowledge base article at Consult your network vendor documentation for the proper network and networking hardware configurations.
  • Ensure that Netflow traffic for a Distributed Virtual Switch is only sent to authorized collector IP addresses. Netflow exports are not encrypted and can contain information about the virtual network. This information increases the potential for sensitive information to be viewed and captured in transit by attackers. If Netflow export is required, verify that all Netflow target IP addresses are correct.
  • Ensure that only authorized administrators have access to virtual networking components by using the role-based access controls. For example, give virtual machine administrators only access to port groups in which their virtual machines reside. Give network administrators access to all virtual networking components but no access to virtual machines. Limiting access reduces the risk of misconfiguration, whether accidental or malicious, and enforces key security concepts of separation of duties and least privilege.
  • Ensure that port groups are not configured to the value of the native VLAN. Physical switches are often configured with a native VLAN, and that native VLAN is often VLAN 1 by default. ESXi does not have a native VLAN. Frames with VLAN specified in the port group have a tag, but frames with VLAN not specified in the port group are not tagged. This can cause a problem because virtual machines that are tagged with a 1 end up belonging to native VLAN of the physical switch.

    For example, frames on VLAN 1 from a Cisco physical switch are untagged because VLAN 1 is the native VLAN on that physical switch. However, frames from the ESXi host that are specified as VLAN 1 are tagged with a 1. As a result, traffic from the ESXi host that is destined for the native VLAN is not routed correctly because it is tagged with a 1 instead of being untagged. Traffic from the physical switch that is coming from the native VLAN is not visible because it is not tagged. If the ESXi virtual switch port group uses the native VLAN ID, traffic from virtual machines on that port is not visible to the native VLAN on the switch because the switch is expecting untagged traffic.

  • Ensure that port groups are not configured to VLAN values reserved by upstream physical switches. Physical switches reserve certain VLAN IDs for internal purposes and often disallow traffic configured to these values. For example, Cisco Catalyst switches typically reserve VLANs 1001–1024 and 4094. Using a reserved VLAN might result in a denial of service on the network.
  • Ensure that port groups are not configured to VLAN 4095 except for Virtual Guest Tagging (VGT). Setting a port group to VLAN 4095 activates VGT mode. In this mode, the virtual switch passes all network frames to the virtual machine without modifying the VLAN tags, leaving it to the virtual machine to deal with them.
  • Restrict port-level configuration overrides on a distributed virtual switch. Port-level configuration overrides are disabled by default. When overrides are enabled, you can use different security settings for a virtual machine than the port-group level settings. Certain virtual machines require unique configurations, but monitoring is essential. If overrides are not monitored, anyone who gains access to a virtual machine with a less secure distributed virtual switch configuration might attempt to exploit that access.
  • Ensure that distributed virtual switch port mirror traffic is sent only to authorized collector ports or VLANs. A vSphere Distributed Switch can mirror traffic from one port to another to allow packet capture devices to collect specific traffic flows. Port mirroring sends a copy of all specified traffic in unencrypted format. This mirrored traffic contains the full data in the packets captured and can result in total compromise of that data if misdirected. If port mirroring is required, verify that all port mirror destination VLAN, port, and uplink IDs are correct.