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 in

volves 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, in

cluding 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_ksock

et(4) node.

HOOKS

This node type supports the following hooks:

upper Connection to the upper protocol layers
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 the node for a

session. This
command takes a struct ng_pptpgre_conf as an argu

ment:

/* 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 window

ing algorithm */
u_int16_t cid; /* my call id */
u_int16_t peerCid; /* peer call id */
u_int16_t recvWin; /* peer recv win

dow 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 acknowledge

ment (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 suc

cessor to PPTP,
removes it.

The remaining fields are as supplied by the PPTP

virtual call
setup process.

NGM_PPTPGRE_GET_CONFIG

Returns the current configuration as a struct

ng_pptpgre_conf.

NGM_PPTPGRE_GET_STATS

This command returns a struct ng_pptpgre_stats con

taining 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 di

rection should
be used instead.

BSD December 7, 2001

BSD