NG_PPTPGRE(4) MidnightBSD 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 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 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:


Connection to the upper protocol layers


Connection to the lower protocol layers


This node type supports the generic control messages, plus the following:


This command resets and configures the node for a session. 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 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 successor to PPTP, removes it.

The remaining fields are as supplied by the PPTP virtual call setup process.


Returns the current configuration 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 sockets. An intermediate node that strips IP headers in one direction should be used instead.

MidnightBSD 0.3 December 7, 2001 MidnightBSD 0.3