NG_PPTPGRE(4)						   BSD 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 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 with-
     out 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 con-
	     figured.  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 acknowledge-
	     ments 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.

BSD
								  March 29, 2008							       BSD