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Transport Mode

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The Transport Mode IPsec policy scenario requires IPsec transport mode protection for all matching traffic. Any matching clear text traffic is dropped until the IKE or AuthIP negotiation has completed successfully. If the negotiation fails, connectivity with the corresponding IP address will remain broken.

An example of a possible Transport Mode scenario is "Secure all unicast data traffic, except ICMP, using IPsec transport mode."

To implement this example programmatically, use the following WFP configuration.

At FWPM_LAYER_IKEEXT_V{4|6} setup MM negotiation policy

  1. Add one or both of the following MM policy provider contexts.

    • For IKE, a policy provider context of type FWPM_IPSEC_IKE_MM_CONTEXT.
    • For AuthIP, a policy provider context of type FWPM_IPSEC_AUTHIP_MM_CONTEXT.

    Note

    A common keying module will be negotiated and the corresponding MM policy will be applied. AuthIP is the preferred keying module if both IKE and AuthIP are supported.

  2. For each of the contexts added in step 1, add a filter with the following properties.

    Filter property Value
    Filtering conditions Empty. All traffic will match the filter.
    providerContextKey GUID of the MM provider context added in step 1.

At FWPM_LAYER_IPSEC_V{4|6} setup QM and EM negotiation policy

  1. Add one or both of the following QM transport mode policy provider contexts.

    • For IKE, a policy provider context of type FWPM_IPSEC_IKE_QM_TRANSPORT_CONTEXT.
    • For AuthIP, a policy provider context of type FWPM_IPSEC_AUTHIP_QM_TRANSPORT_CONTEXT. This context can optionally contain the AuthIP Extended Mode (EM) negotiation policy.

    Note

    A common keying module will be negotiated and the corresponding QM policy will be applied. AuthIP is the preferred keying module if both IKE and AuthIP are supported.

  2. For each of the contexts added in step 1, add a filter with the following properties.

    Filter property Value
    Filtering conditions Empty. All traffic will match the filter.
    providerContextKey GUID of the QM provider context added in step 1.

At FWPM_LAYER_INBOUND_TRANSPORT_V{4|6} setup inbound per-packet filtering rules

  1. Add a filter with the following properties.

    Filter property Value
    FWPM_CONDITION_IP_LOCAL_ADDRESS_TYPE filtering condition NlatUnicast
    action.type FWP_ACTION_CALLOUT_TERMINATING
    action.calloutKey FWPM_CALLOUT_IPSEC_INBOUND_TRANSPORT_V{4|6}

  2. Exempt ICMP traffic from IPsec by adding a filter with the following properties.

    Filter property Value
    FWPM_CONDITION_IP_LOCAL_ADDRESS_TYPEfiltering condition NlatUnicast
    FWPM_CONDITION_IP_PROTOCOL filtering condition IPPROTO_ICMP{V6}These constants are defined in winsock2.h.
    action.type FWP_ACTION_PERMIT
    weight FWPM_WEIGHT_RANGE_IKE_EXEMPTIONS

At FWPM_LAYER_OUTBOUND_TRANSPORT_V{4|6} setup outbound per-packet filtering rules

  1. Add a filter with the following properties.

    Filter property Value
    FWPM_CONDITION_IP_LOCAL_ADDRESS_TYPE filtering condition NlatUnicast
    action.type FWP_ACTION_CALLOUT_TERMINATING
    action.calloutKey FWPM_CALLOUT_IPSEC_OUTBOUND_TRANSPORT_V{4|6}

  2. Exempt ICMP traffic from IPsec by adding a filter with the following properties.

    Filter property Value
    FWPM_CONDITION_IP_LOCAL_ADDRESS_TYPE filtering condition NlatUnicast
    FWPM_CONDITION_IP_PROTOCOL filtering condition IPPROTO_ICMP{V6}These constants are defined in winsock2.h.
    action.type FWP_ACTION_PERMIT
    weight FWPM_WEIGHT_RANGE_IKE_EXEMPTIONS

Sample code: Using Transport Mode

Filtering Layer Identifiers

Provider Context Types

Filtering Conditions

FWPM_ACTION0

Built-in Callout Identifiers