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) 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
configured. 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
- 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.