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NG_PPTPGRE(4)		     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  en-
     capsulation,  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 config-
		   urable 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  corre-
	     sponding  session_hhhh  hook  is  not connected, upper hook will be
	     configured.  This command takes a struct ng_pptpgre_conf as an  ar-
	     gument:

	     /* 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 acknowledge-
	     ments with every data packet, which is probably helpful as well.

	     enableWindowing enables the PPTP packet windowing mechanism  speci-
	     fied  by  the protocol.  Disabling this will cause the node to vio-
	     late 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  configura-
	     tion 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,  re-
	     turning 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.

FreeBSD 8.0			 March 29, 2008 		   NG_PPTPGRE(4)
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