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

NAME
     ng_pptpgre - PPTP GRE protocol netgraph node type

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

DESCRIPTION
     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.

HOOKS
     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

CONTROL MESSAGES
     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
          argument:

          /* 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
          process.

     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.

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

SYSCTL VARIABLES
     A set of sysctl(8) variables controls ability of this node to deal with
     some amount of packet reorder that sometimes happens in transit.  Packet
     reorder results in packet drops (unless the order is restored) as PPP
     protocol can not deliver reordered data.  These variables are shown below
     together with their default value and meaning:

     net.graph.pptpgre.reorder_max: 1
             Defines maximum length of node's private reorder queue used to
             keep data waiting for late packets.  Zero value disables
             reordering.  Default value allows the node to restore the order
             for two packets swapped in transit.  Greater values allow the
             node to deliver packets being late after more packets in sequence
             at cost of increased kernel memory usage.

     net.graph.pptpgre.reorder_timeout: 1
             Defines time value in miliseconds used to wait for late packets.

SEE ALSO
     netgraph(4), ng_ksocket(4), ng_ppp(4), ngctl(8), sysctl(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.

HISTORY
     The ng_pptpgre node type was implemented in FreeBSD 4.0.

AUTHORS
     Archie Cobbs <archie@FreeBSD.org>

BUGS
     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 13.1-RELEASE-p6        November 4, 2018        FreeBSD 13.1-RELEASE-p6