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     ng_pptpgre — PPTP GRE protocol netgraph node type


     #include <sys/types.h>
     #include <netgraph/ng_pptpgre.h>


     The pptpgre node type performs Generic Routing Encapsulation (GRE) over
     IP for the PPTP protocol as specified by RFC 2637.  This involves packet
     encapsulation, sequencing, acknowledgement, and an adaptive timeout
     sliding window mechanism.  This node type does not handle any of the TCP
     control protocol or call negotiation defined by PPTP.

     This node type expects to receive complete IP packets, including the IP
     header, on the “lower” hook, but it transmits outgoing frames without any
     IP header.  The typical use for this node type would be to connect the
     “upper” hook to one of the link hooks of a ng_ppp(4) node, and the
     “lower” hook to the “inet/raw/gre” hook of a ng_ksocket(4) node.


     This node type supports the following hooks:

     session_hhhh  Session 0xhhhh data packets to the upper protocol layers
     upper         Same as session_hhhh, but for single session with
                   configurable cid (legacy)
     lower         Connection to the lower protocol layers


     This node type supports the generic control messages, plus the following:

             This command resets and configures hook for a session. If
             corresponding session_hhhh hook is not connected, upper hook will
             be configured.  This command takes a struct ng_pptpgre_conf as an

             /* Configuration for a session */
             struct ng_pptpgre_conf {
                 u_char      enabled;          /* enables traffic flow */
                 u_char      enableDelayedAck; /* enables delayed acks */
                 u_char      enableAlwaysAck;  /* always send ack with data */
                 u_char      enableWindowing;  /* enable windowing algorithm */
                 u_int16_t   cid;              /* my call id */
                 u_int16_t   peerCid;          /* peer call id */
                 u_int16_t   recvWin;          /* peer recv window size */
                 u_int16_t   peerPpd;          /* peer packet processing delay
                                                  (in 1/10 of a second) */

             The enabled field enables traffic flow through the node.  The
             enableDelayedAck field enables delayed acknowledgement (maximum
             250 milliseconds), which is a useful optimization and should
             generally be turned on.  enableAlwaysAck field enables sending
             acknowledgements with every data packet, which is probably
             helpful as well.

             enableWindowing enables the PPTP packet windowing mechanism
             specified by the protocol.  Disabling this will cause the node to
             violate the protocol, possibly confusing other PPTP peers, but
             often results in better performance.  The windowing mechanism is
             a design error in the PPTP protocol; L2TP, the successor to PPTP,
             removes it.

             The remaining fields are as supplied by the PPTP virtual call
             setup process.

             Takes two byte argument as cid and returns the current
             configuration as a struct ng_pptpgre_conf.

             This command returns a struct ng_pptpgre_stats containing various
             node statistics.

             This command resets the node statistics.

             This command atomically gets and resets the node statistics,
             returning a struct ng_pptpgre_stats.


     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when both hooks have been disconnected.


     netgraph(4), ng_ksocket(4), ng_ppp(4), ngctl(8)

     K. Hamzeh, G. Pall, W. Verthein, J. Taarud, W. Little, and G. Zorn,
     Point-to-Point Tunneling Protocol (PPTP), RFC 2637.

     S. Hanks, T. Li, D. Farinacci, and P. Traina, Generic Routing
     Encapsulation over IPv4 networks, RFC 1702.


     The ng_pptpgre node type was implemented in FreeBSD 4.0.


     Archie Cobbs ⟨


     The node should not expect incoming GRE packets to have an IP header.
     This behavior is inherited from the (converse) behavior of raw IP
     sockets.  An intermediate node that strips IP headers in one direction
     should be used instead.