---
name: "ng_pptpgre"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/ng_pptpgre"
---

# ng\_pptpgre(4)

PPTP GRE protocol netgraph node type

## 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 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)](/ng_ppp/4.md) node, and the “lower” hook to the “inet/raw/gre” hook of a [ng\_ksocket(4)](/ng_ksocket/4.md) 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 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.

- 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* 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)](/netgraph/4.md), [ng\_ksocket(4)](/ng_ksocket/4.md), [ng\_ppp(4)](/ng_ppp/4.md), [ngctl(8)](/ngctl/8.md) 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.