NF_RULE¶

A rule defines the filtering flag for network activity, described by 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 a 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 from 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 from the network remoteIpAddress & remoteIpAddressMask.
filteringFlag: A value from NF_FILTERING_FLAG enumeration.

All ports and IP addresses in the rule must have network byte order. Zero in a rule field means that its value is undefined, and the field should 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, i.e., the packets will be indicated via NF_EventHandler methods.
NF_SUSPENDED = 4: Suspend indicating new data packets via NF_EventHandler. It is possible to change this flag for a connection or UDP socket using nf_tcpSetConnectionState or nf_udpSetConnectionState.
NF_INDICATE_CONNECT_REQUESTS = 16: Call the tcpConnectRequest event before establishing an outgoing TCP connection. In this event it is possible to modify the fields filteringFlag and remoteAddress in the NF_TCP_CONN_INFO structure. The changes are applied to the connection.
NF_DISABLE_REDIRECT_PROTECTION = 32: Disable blocking indicating connect requests for outgoing connections of local proxies. When this flag is used with NF_INDICATE_CONNECT_REQUESTS, tcpConnectRequest is called for all outgoing connections. If your filter redirects TCP connections, it is necessary to manually prevent possible filtering loops. I.e., detect the local proxies of antiviruses and other filters and don’t redirect their connections. To detect the proxies it is possible to use the function nf_tcpIsProxy.
NF_PEND_CONNECT_REQUEST = 64: Pend the connect request to complete it later using nf_complete(TCP|UDP)ConnectRequest. This flag can be assigned only in (tcp|udp)ConnectRequest events.
NF_FILTER_AS_IP_PACKETS = 128: This flag instructs the driver to apply the rule to IP traffic and indicate IP packets via NF_IPEventHandler functions. The flags NF_ALLOW, NF_BLOCK will be applied to IP packets that meet the rule conditions. When the NF_BLOCK flag is specified in a rule, the packets are silently blocked without indication to the user-mode API. The flags NF_FILTER and NF_FILTER_AS_IP_PACKETS are mutually exclusive. When they are specified together, the driver takes into account only NF_FILTER_AS_IP_PACKETS. IP filtering is supported only with the WFP driver.
NF_READONLY = 256: This flag can be added with NF_FILTER_AS_IP_PACKETS to filter the packets in read-only mode. In this case the packets are not blocked, and are indicated to NF_IPEventHandler functions only for monitoring.
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., it 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: This flag can be used with the WFP driver on Windows 8/10. Redirect the outgoing TCP connections inline in the driver to the address specified in redirectTo. The additional fields redirectTo and localProxyProcessId required for redirection are available in the NF_RULE_EX structure.
NF_BYPASS_IP_PACKETS = 2048: When the NF_FILTER_AS_IP_PACKETS flag is enabled, NF_BYPASS_IP_PACKETS can be added to bypass the traffic as IP packets. I.e., it works as NF_ALLOW for IP packets.