Overview of Hyper-V Extensible Switch Ports

Each network connection to the Hyper-V extensible switch is represented by a port. The extensible switch interface creates and configures a port before a network connection is made. After the network connection is torn down, the interface may delete the port or reuse it for another network connection.

Every Hyper-V child partition that is configured with a network interface is assigned a port on the extensible switch. When a Hyper-V child partition is started, the extensible switch interface creates a port before the virtual machine (VM) network adapter is exposed within the guest operating system. After the VM network adapter is exposed and initialized, the extensible switch interface creates a network connection between the VM network adapter and the extensible switch port. If the child partition is stopped, the extensible switch interface first deletes the network connection and then deletes the extensible switch port.

When an extensible switch port is created, it is configured with a unique identifier and name. After it is created, the extensible switch port can be provisioned with policies that define various attributes for the management of packet traffic over the port. For example, standard port policies can be defined for virtual LAN (VLAN) attributes and access restrictions for port traffic. In addition, independent software vendors (ISVs) can define custom policies that individual ports can be provisioned with. For more information, see Port Policies.

Extensible switch ports consist of the following types:

Validation ports
Validation ports are used to validate and verify port settings. These ports are temporary and are created under certain conditions.

For example, when a Hyper-V child partition is created or reconfigured for network access, the extensible switch interface creates a validation port. The interface uses this port to verify the settings for the network connection to the virtual machine (VM) network adapter of the partition. After the verification is completed, the validation port is deleted and an operational port is created.

For more information, see Validation Ports.

Operational ports
Operational ports are created to host an extensible switch network adapter connection. When an operational port is created, it is assigned a port type. This port type is in effect after the port is created and before it is torn down. For ports assigned to Hyper-V child partitions, the operational port type stays in effect while the partition is running and operational.

For more information, see Operational Ports.

Extensible switch extensions are notified of port creation, update and deletion through the following extensible switch object identifier (OID) requests:

OID_SWITCH_PORT_CREATE
The protocol edge of the extensible switch issues an OID set request of OID_SWITCH_PORT_CREATE to notify extensible switch extensions about the creation of an extensible switch port.

The extension can veto the creation notification by returning STATUS_DATA_NOT_ACCEPTED for the OID request. For example, if an extension cannot allocate resources to enforce its configured policies on the port, the extension vetoes the creation notification.

If the extension accepts the creation notification, it must forward the OID request down the extensible switch driver stack. The extension monitors the completion status of this OID request to determine whether underlying extensions have vetoed the port creation notification.

Extensions cannot forward packets to the newly created port until a network connection is created. For more information on this process, see Hyper-V Extensible Switch Network Adapters.

OID_SWITCH_PORT_UPDATED
The protocol edge of the extensible switch issues an OID set request of OID_SWITCH_PORT_UPDATED to notify extensible switch extensions that an extensible switch port’s parameters are being updated. The OID will only be issued for ports that have already been created, and have not yet begun the teardown/delete process. Currently only the PortFriendlyName field is subject to update after creation.

The protocol edge of the extensible switch issues this OID request when the previous network connection to the port has been torn down and all OID requests to the port have been completed.

Note This OID request could be issued if a network adapter connection was not previously made to the port.

The extension must always forward this OID set request down the extensible switch driver stack. The extension must not fail the request.

OID_SWITCH_PORT_TEARDOWN
The protocol edge of the extensible switch issues an OID set request of OID_SWITCH_PORT_TEARDOWN to notify extensible switch extensions that an extensible switch port is being deleted. The protocol edge of the extensible switch issues this OID request when the previous network connection to the port has been torn down and all OID requests to the port have been completed.

Note This OID request could be issued if a network adapter connection was not previously made to the port.

The extension must always forward this OID set request down the extensible switch driver stack. The extension must not fail the request.

After the extension forwards this OID request, it can no longer issue OID requests for the port being deleted.

OID_SWITCH_PORT_DELETE
The protocol edge of the extensible switch issues an OID set request of OID_SWITCH_PORT_DELETE to notify extensible switch extensions that an extensible switch port has been deleted. The protocol edge of the extensible switch issues this OID request after it issues the OID_SWITCH_PORT_TEARDOWN request and OID requests that target the port have been completed.

The extension must always forward this OID set request down the extensible switch driver stack. The extension must not fail the request.

All extensible switch ports that are created for network connections are assigned an identifier greater than NDIS_SWITCH_DEFAULT_PORT_ID. The NDIS_SWITCH_DEFAULT_PORT_ID identifier is reserved and used in the following ways:

  • The source port identifier for a packet is stored in the packet's out-of-band (OOB) forwarding context that is associated with its NET_BUFFER_LIST structure. A source port identifier of NDIS_SWITCH_DEFAULT_PORT_ID specifies that the packet originated from the extensible switch extension and not from an extensible switch port. A packet with a source port identifier of NDIS_SWITCH_DEFAULT_PORT_ID is trusted and bypasses the extensible switch port policies, such as access control lists (ACLs) and quality of service (QoS).

    The extension may want the packet to be treated as if it originated from a particular port. This allows the policies for that port to be applied to the packet. The extension calls SetNetBufferListSource to change the source port for the packet.

    However, there may be situations where the extension may want to assign the packet's source port identifier to NDIS_SWITCH_DEFAULT_PORT_ID. For example, the extension may want to set the source port identifier to NDIS_SWITCH_DEFAULT_PORT_ID for proprietary control packets that are sent to a device on the external network.

    For more information about the forwarding context, see Hyper-V Extensible Switch Forwarding Context.

  • Object identifier (OID) requests of OID_SWITCH_NIC_REQUEST are issued by the extensible switch interface to encapsulate OID requests that are issued to the extensible switch external network adapter. For example, hardware offload OID requests are encapsulated by the interface before they are issued down the extensible switch driver stack.

    An extension can also issue encapsulated OID requests in order to forward requests down the extensible switch control path. This allows extensions to query or configure the capabilities of an underlying physical network adapter.

    The InformationBuffer member of the NDIS_OID_REQUEST structure for this OID request contains a pointer to an NDIS_SWITCH_NIC_OID_REQUEST structure. If the SourcePortId member is set to NDIS_SWITCH_DEFAULT_PORT_ID, this specifies that the OID request was originated by the extensible switch interface. If the DestinationPortId is set to NDIS_SWITCH_DEFAULT_PORT_ID, this specifies that the OID request is targeted for processing by an extension in the extensible switch driver stack.

    For more information about the control path for OID requests, see Hyper-V Extensible Switch Control Path for OID Requests.

  • NDIS status indications of NDIS_STATUS_SWITCH_NIC_STATUS are issued by the miniport edge of the extensible switch to encapsulate a status indication from the extensible switch external network adapter.

    An extension can also issue encapsulated NDIS status indications in order to forward indications up the extensible switch control path. This allows extensions to change the reported capabilities of an underlying physical network adapter.

    The StatusBuffer member of the NDIS_STATUS_INDICATION structure for this indication contains a pointer to an NDIS_SWITCH_NIC_STATUS_INDICATION structure. If the SourcePortId member is set to NDIS_SWITCH_DEFAULT_PORT_ID, this specifies that the status indication was originated by the extensible switch interface. If the DestinationPortId is set to NDIS_SWITCH_DEFAULT_PORT_ID, this specifies that the OID request is targeted for processing by an extension in the extensible switch driver stack.

    For more information about the control path for NDIS status indications, see Hyper-V Extensible Switch Control Path for NDIS Status Indications.

The extensible switch interface maintains a reference counter for each port that has been created. A port will not be deleted if its reference counter has a nonzero value. The interface provides the following handler functions for incrementing or decrementing an extensible switch port's reference counters:

ReferenceSwitchPort
The extensible switch extension calls this function to increment a port's reference counter. While the reference counter has a nonzero value, the protocol edge of the extensible switch will not issue an object identifier (OID) set request of OID_SWITCH_PORT_DELETE to delete the extensible switch port.

The extension must call ReferenceSwitchPort before it performs any operation that requires the port to be in an active state. For example, the extension must call ReferenceSwitchPort before it issues an OID method request of OID_SWITCH_PORT_PROPERTY_ENUM.

Note The extension must not call ReferenceSwitchPort for a port after it receives an OID set request of OID_SWITCH_PORT_TEARDOWN for that port.

DereferenceSwitchPort
The extensible switch extension calls this function to decrement a port's reference counter.

The extension must call DereferenceSwitchPort after the operation being performed on the port has completed. For example, if the extension called ReferenceSwitchPort before if issued an OID_SWITCH_PORT_PROPERTY_ENUM request, the extension must call DereferenceSwitchPort after the OID request has completed.

Note NDIS ports and extensible switch ports are different objects. Packets that move through the extensible switch data path are always assigned to the NDIS port number of NDIS_DEFAULT_PORT_NUMBER. However, the packet's source and destination extensible switch port number can be a value of NDIS_SWITCH_DEFAULT_PORT_ID or greater. For more information, see Hyper-V Extensible Switch Data Path.