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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 slid-
     ing window	mechanism.  This node type does	not handle any of the TCP con-
     trol 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 layers

     upper	   Same	as session_hhhh, but for single	session	with config-
		   urable 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 corre-
	  sponding session_hhhh	hook is	not connected, upper hook will be con-
	  figured.  This command takes a struct	ng_pptpgre_conf	as an argu-

	  /* 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 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 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, return-
	  ing a	struct ng_pptpgre_stats.

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

     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 reorder-
	     ing.  Default value allows	the node to restore the	order for two
	     packets swapped in	transit.  Greater values allow the node	to de-
	     liver 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.

     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.

     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 sock-
     ets.  An intermediate node	that strips IP headers in one direction	should
     be	used instead.

FreeBSD	13.0		       November	4, 2018			  FreeBSD 13.0


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