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NG_PPTPGRE(4)          FreeBSD Kernel Interfaces Manual          NG_PPTPGRE(4)

     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

     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:

     NGM_PPTPGRE_SET_CONFIG (setconfig)
          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 include ack with data */
              u_char      enableWindowing;  /* enable windowing algorithm */
              uint16_t    cid;              /* my call id */
              uint16_t    peerCid;          /* peer call id */
              uint16_t    recvWin;          /* peer recv window size */
              uint16_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

     NGM_PPTPGRE_GET_CONFIG (getconfig)
          Takes two byte argument as cid and returns the current configuration
          as a struct ng_pptpgre_conf.

     NGM_PPTPGRE_GET_STATS (getstats)
          This command returns a struct ng_pptpgre_stats containing various
          node statistics.

     NGM_PPTPGRE_CLR_STATS (clrstats)
          This command resets the node statistics.

     NGM_PPTPGRE_GETCLR_STATS (getclrstats)
          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.

FreeBSD 11.0-PRERELEASE        November 13, 2012       FreeBSD 11.0-PRERELEASE


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