NAME¶
ng_mppc —
Microsoft MPPC/MPPE
compression and encryption netgraph node type
SYNOPSIS¶
#include <sys/types.h>
#include <netgraph/ng_mppc.h>
DESCRIPTION¶
The
mppc node type implements the Microsoft Point-to-Point
Compression (MPPC) and Microsoft Point-to-Point Encryption (MPPE)
sub-protocols of the PPP protocol. These protocols are often used in
conjunction with the Point-to-Point Tunneling Protocol (PPTP).
The node has two hooks,
comp
for compression and
decomp
for decompression. Typically one or both of
these hooks would be connected to the
ng_ppp(4) node type
hook of the same name. Each direction of traffic flow is independent of the
other.
HOOKS¶
This node type supports the following hooks:
comp
- Connection to ng_ppp(4)
comp
hook. Incoming frames are compressed and/or
encrypted, and sent back out the same hook.
decomp
- Connection to ng_ppp(4)
decomp
hook. Incoming frames are decompressed
and/or decrypted, and sent back out the same hook.
CONTROL MESSAGES¶
This node type supports the generic control messages, plus the following:
NGM_MPPC_CONFIG_COMP
- This command resets and configures the node for a session
in the outgoing traffic direction (i.e., for compression and/or
encryption). This command takes a
struct
ng_mppc_config
as an argument:
/* Length of MPPE key */
#define MPPE_KEY_LEN 16
/* MPPC/MPPE PPP negotiation bits */
#define MPPC_BIT 0x00000001 /* mppc compression bits */
#define MPPE_40 0x00000020 /* use 40 bit key */
#define MPPE_56 0x00000080 /* use 56 bit key */
#define MPPE_128 0x00000040 /* use 128 bit key */
#define MPPE_BITS 0x000000e0 /* mppe encryption bits */
#define MPPE_STATELESS 0x01000000 /* use stateless mode */
#define MPPC_VALID_BITS 0x010000e1 /* possibly valid bits */
/* Configuration for a session */
struct ng_mppc_config {
u_char enable; /* enable */
u_int32_t bits; /* config bits */
u_char startkey[MPPE_KEY_LEN]; /* start key */
};
The enabled
field enables traffic flow through the
node. The bits
field contains the bits as
negotiated by the Compression Control Protocol (CCP) in PPP. The
startkey
is only necessary if MPPE was negotiated,
and must be equal to the session start key as defined for MPPE. This key
is based on the MS-CHAP credentials used at link authentication time.
NGM_MPPC_CONFIG_DECOMP
- This command resets and configures the node for a session
in the incoming traffic direction (i.e., for decompression and/or
decryption). This command takes a
struct
ng_mppc_config
as an argument.
NGM_MPPC_RESETREQ
- This message contains no arguments, and is bi-directional.
If an error is detected during decompression, this message is sent by the
node to the originator of the
NGM_MPPC_CONFIG_DECOMP
message that initiated the
session. The receiver should respond by sending a PPP CCP Reset-Request to
the peer.
This message may also be received by this node type when a CCP Reset-Request
is received by the local PPP entity. The node will respond by flushing its
outgoing compression and encryption state so the remote side can
resynchronize.
SHUTDOWN¶
This node shuts down upon receipt of a
NGM_SHUTDOWN
control message, or when both hooks have been disconnected.
COMPILATION¶
The kernel options
NETGRAPH_MPPC_COMPRESSION
and
NETGRAPH_MPPC_ENCRYPTION
are supplied to selectively
compile in either or both capabilities. At least one of these must be defined,
or else this node type is useless.
The MPPC protocol requires proprietary compression code available from Hi/Fn
(formerly STAC). These files must be obtained elsewhere and added to the
kernel sources before this node type will compile with the
NETGRAPH_MPPC_COMPRESSION
option.
SEE ALSO¶
netgraph(4),
ng_ppp(4),
ngctl(8)
G. Pall, Microsoft
Point-To-Point Compression (MPPC) Protocol, RFC
2118.
G. S. Pall and G.
Zorn, Microsoft Point-To-Point Encryption (MPPE)
Protocol,
draft-ietf-pppext-mppe-04.txt.
K. Hamzeh, G.
Pall, W. Verthein, J.
Taarud, W. Little, and G.
Zorn, Point-to-Point Tunneling Protocol
(PPTP), RFC 2637.
AUTHORS¶
Archie Cobbs ⟨archie@FreeBSD.org⟩
BUGS¶
In PPP, encryption should be handled by the Encryption Control Protocol (ECP)
rather than CCP. However, Microsoft combined both compression and encryption
into their ``compression'' algorithm, which is confusing.