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
               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 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.

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

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

       NGM_PPTPGRE_CLR_STATS
               This command resets the node statistics.

       NGM_PPTPGRE_GETCLR_STATS
               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.

SEE ALSO

       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.

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.

Debian                                           March 29, 2008                                    NG_PPTPGRE(4)