NF_RULE¶

A rule defines the filtering flag for network activity described by the other rule fields.

typedef struct _NF_RULE
{
        int             protocol;       // IPPROTO_TCP or IPPROTO_UDP
        unsigned long   processId;      // Process identifier
        unsigned char   direction;      // See NF_DIRECTION (NF_D_IN, NF_D_OUT or NF_D_BOTH)
        unsigned short  localPort;      // Local port
        unsigned short  remotePort;     // Remote port
        unsigned short  ip_family;      // AF_INET for IPv4 and AF_INET6 for IPv6

        // Local IP (or network if localIpAddressMask is not zero)
        unsigned char   localIpAddress[NF_MAX_IP_ADDRESS_LENGTH];

        // Local IP mask
        unsigned char   localIpAddressMask[NF_MAX_IP_ADDRESS_LENGTH];

        // Remote IP (or network if remoteIpAddressMask is not zero)
        unsigned char   remoteIpAddress[NF_MAX_IP_ADDRESS_LENGTH];

        // Remote IP mask
        unsigned char   remoteIpAddressMask[NF_MAX_IP_ADDRESS_LENGTH];

        unsigned long   filteringFlag;  // See NF_FILTERING_FLAG
} NF_RULE, *PNF_RULE;

protocol: Network protocol (IPPROTO_TCP or IPPROTO_UDP). Zero means any protocol.
processId: Process identifier. Zero means any process.
direction: The direction of network activity. Specify NF_D_IN for inbound TCP connections and UDP datagrams, NF_D_OUT for outbound TCP connections and UDP datagrams. Zero or NF_D_BOTH means any direction.
localPort: Local port.
remotePort: Remote port.
ip_family: Describes the family of IP addresses in the rule. Specify AF_INET for IPv4 and AF_INET6 for IPv6. If ip_family is zero, the driver doesn’t use the IP addresses specified in the rule.
localIpAddress: Local IPv4 or IPv6 address. Zero means any address.
localIpAddressMask: If localIpAddressMask is not zero, the rule will be applied to network activity with a local address within the network localIpAddress & localIpAddressMask.
remoteIpAddress: Remote IPv4 or IPv6 address. Zero means any address.
remoteIpAddressMask: If remoteIpAddressMask is not zero, the rule will be applied to network activity with a remote address within the network remoteIpAddress & remoteIpAddressMask.
filteringFlag: A value from NF_FILTERING_FLAG enumeration.

All ports and IP addresses in the rule must be in network byte order. Zero in a rule field means that its value is undefined, and the field will be ignored.

The following values are allowed for filteringFlag:

NF_ALLOW = 0: Allow the activity without filtering transmitted packets. This flag is applied to all network activity that is not described by any rule.
NF_BLOCK = 1: Block the activity.
NF_FILTER = 2: Filter the transmitted packets. That is, the packets will be indicated via NF_EventHandler methods.
NF_INDICATE_CONNECT_REQUESTS = 16: The tcpConnectRequest event is called before establishing an outgoing TCP connection. In this event it is possible to modify the filteringFlag and remoteAddress fields in the NF_TCP_CONN_INFO structure. The changes are applied to the connection.
NF_PEND_CONNECT_REQUEST = 64: Pends the connect request to complete it later using nf_completeTCPConnectRequest. This flag can be assigned only from (tcp|udp)ConnectRequest event handlers.
NF_CONTROL_FLOW = 512: This flag can be added instead of NF_FILTER to apply flow control contexts for limiting and counting TCP/UDP traffic. When NF_CONTROL_FLOW is specified instead of NF_FILTER, the driver indicates only tcpConnectRequest/tcpConnected/tcpClosed and udpCreated/udpClosed events, i.e. doesn’t indicate the data packets for filtering. In this case there are no delays because of filtering the packets in user mode, but it is possible to use the control contexts to count and limit the traffic.
NF_REDIRECT = 1024: Redirects outgoing TCP connections inline in the driver to the address specified in redirectTo. The additional redirectTo field required for redirection is available in the NF_RULE_EX structure.