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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 (setconfig)
	  This command resets and configures hook for a session.  If correspond-
	  ing 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 pro-
     tocol can not deliver reordered data.  These variables are shown below  to-
     gether 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 pack-
	     ets  being late after more packets in sequence at cost of increased
	     kernel memory usage.

     net.graph.pptpgre.reorder_timeout: 1
	     Defines time value in milliseconds 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 ports 15.quarterly	November 4, 2018		   NG_PPTPGRE(4)

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