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.\" Author: Archie Cobbs <archie@FreeBSD.org>
.\"
.\" $FreeBSD$
.\" $Whistle: ng_pptpgre.8,v 1.2 1999/12/08 00:20:53 archie Exp $
.\"
.Dd November 4, 2018
.Dt NG_PPTPGRE 4
.Os
.Sh NAME
.Nm ng_pptpgre
.Nd PPTP GRE protocol netgraph node type
.Sh SYNOPSIS
.In sys/types.h
.In netgraph/ng_pptpgre.h
.Sh DESCRIPTION
The
.Nm 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.
.Pp
This node type expects to receive complete IP packets,
including the IP header, on the
.Dq Li lower
hook, but it transmits outgoing frames without any IP header.
The typical use for this node type would be to connect the
.Dq Li upper
hook to one of the link hooks of a
.Xr ng_ppp 4
node, and the
.Dq Li lower
hook to the
.Dq Li "inet/raw/gre"
hook of a
.Xr ng_ksocket 4
node.
.Sh HOOKS
This node type supports the following hooks:
.Bl -tag -width ".Va session_hhhh"
.It Va session_hhhh
Session 0xhhhh data packets to the upper protocol layers
.It Va upper
Same as session_hhhh, but for single session with configurable cid (legacy)
.It Va lower
Connection to the lower protocol layers
.El
.Sh CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
.Bl -tag -width foo
.It Dv NGM_PPTPGRE_SET_CONFIG Pq Ic setconfig
This command resets and configures hook for a session.
If corresponding
session_hhhh hook is not connected, upper hook will be configured.
This command takes a
.Vt "struct ng_pptpgre_conf"
as an argument:
.Bd -literal
/* 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) */
};
.Ed
.Pp
The
.Va enabled
field enables traffic flow through the node.
The
.Va enableDelayedAck
field enables delayed acknowledgement (maximum 250 milliseconds), which
is a useful optimization and should generally be turned on.
.Va enableAlwaysAck
field enables sending acknowledgements with every data packet, which
is probably helpful as well.
.Pp
.Va 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.
.Pp
The remaining fields are as supplied by the PPTP virtual call setup process.
.It Dv NGM_PPTPGRE_GET_CONFIG Pq Ic getconfig
Takes two byte argument as cid and returns the current configuration as a
.Vt "struct ng_pptpgre_conf" .
.It Dv NGM_PPTPGRE_GET_STATS Pq Ic getstats
This command returns a
.Vt "struct ng_pptpgre_stats"
containing various node statistics.
.It Dv NGM_PPTPGRE_CLR_STATS Pq Ic clrstats
This command resets the node statistics.
.It Dv NGM_PPTPGRE_GETCLR_STATS Pq Ic getclrstats
This command atomically gets and resets the node statistics, returning a
.Vt "struct ng_pptpgre_stats" .
.El
.Sh SHUTDOWN
This node shuts down upon receipt of a
.Dv NGM_SHUTDOWN
control message, or when both hooks have been disconnected.
.Sh SYSCTL VARIABLES
A set of
.Xr 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:
.Bl -tag -width indent
.It Va 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 packets being late after more
packets in sequence at cost of increased kernel memory usage.
.It Va net.graph.pptpgre.reorder_timeout: 1
Defines time value in miliseconds used to wait for late packets.
.El
.Sh SEE ALSO
.Xr netgraph 4 ,
.Xr ng_ksocket 4 ,
.Xr ng_ppp 4 ,
.Xr ngctl 8 ,
.Xr sysctl 8
.Rs
.%A K. Hamzeh
.%A G. Pall
.%A W. Verthein
.%A J. Taarud
.%A W. Little
.%A G. Zorn
.%T "Point-to-Point Tunneling Protocol (PPTP)"
.%O RFC 2637
.Re
.Rs
.%A S. Hanks
.%A T. \&Li
.%A D. Farinacci
.%A P. Traina
.%T "Generic Routing Encapsulation over IPv4 networks"
.%O RFC 1702
.Re
.Sh HISTORY
The
.Nm
node type was implemented in
.Fx 4.0 .
.Sh AUTHORS
.An Archie Cobbs Aq Mt archie@FreeBSD.org
.Sh 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.