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NG_PPTPGRE(4)		 BSD 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:

	     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

	     /* 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 gen‐
	     erally be turned on.  enableAlwaysAck field enables sending
	     acknowledgements with every data packet, which is probably help‐
	     ful as well.

	     enableWindowing enables the PPTP packet windowing mechanism spec‐
	     ified 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.

	     Takes two byte argument as cid and returns the current configura‐
	     tion as a struct ng_pptpgre_conf.

	     This command returns a struct ng_pptpgre_stats containing various
	     node statistics.

	     This command resets the node statistics.

	     This command atomically gets and resets the node statistics,
	     returning a struct ng_pptpgre_stats.

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

     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.

     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.

BSD				March 29, 2008				   BSD

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