freebsd-dev/sys/modules/netgraph/ppp/ng_ppp.4

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.\" Author: Archie Cobbs <archie@whistle.com>
.\"
.\" $FreeBSD$
.\" $Whistle: ng_ppp.8,v 1.3 1999/01/25 23:46:27 archie Exp $
.\"
.Dd January 19, 1999
.Dt NG_PPP 8
.Os FreeBSD
.Sh NAME
.Nm ng_ppp
.Nd PPP protocol netgraph node type
.Sh SYNOPSIS
.Fd #include <netgraph/ng_ppp.h>
.Sh DESCRIPTION
The
.Nm ppp
node type performs multiplexing for the PPP protocol.  It handles
only packets that contain data, and forwards protocol negotiation
and control packets to a separate controlling entity (e.g., a
user-land daemon).  This approach combines the fast dispatch of
kernel implementations with the configuration flexibility of a
user-land implementations.  The PPP node type directly supports
multi-link PPP, Van Jacobsen compression, PPP compression, PPP
encryption, and the IP, IPX, and AppleTalk protocols.  A single
PPP node corresponds to one PPP multi-link bundle.
.Pp
There is a separate hook for each PPP link in the bundle, plus
several hooks corresponding to the directly supported protocols.
For compression and encryption, separate attached nodes are required
to do the actual work.  The node type used will of course depend
on the algorithm negotiated.  There is also a
.Dv bypass
hook which is used to handle any protocol not directly supported
by the node. This includes all of the control protocols: LCP, IPCP,
CCP, etc.  Typically this node is connected to a user-land daemon
via a
.Xr ng_socket 8
type node.
.Sh ENABLING FUNCTIONALITY
In general, the PPP node enables a specific link or functionality when
(a) a
.Dv NGM_PPP_SET_CONFIG
message has been received which enables it, and
(b) the corresponding hook(s) are connected.
This allows the controlling entity to use either method (a) or (b)
(or both) to control the node's behavior.
When a link is connected but disabled, traffic can still flow on
the link via the
.Dv bypass
hook (see below).
.Sh LINK HOOKS
During normal operation, the individual PPP links are connected to hooks
.Dv link0 ,
.Dv link1 ,
etc.  Up to
.Dv NG_PPP_MAX_LINKS
links are supported.
These device-independent hooks transmit and receive full PPP
frames, which include the PPP protocol, address, control, and
information fields, but no checksum or other link-specific fields.
.Pp
On outgoing frames, when protocol compression
has been enabled and the protocol number is suitable for compression,
the protocol field will be compressed (i.e., sent as one byte
instead of two).  Either compressed or uncompressed protocol fields
are accepted on incoming frames.  Similarly, if address and control
field compression has been enabled for the link, the address and
control fields will be omitted (except for LCP frames as required
by the standards).  Incoming frames have the address and control fields
stripped automatically if present.
.Pp
Since all negotiation is handled outside the PPP node, the links
should not be connected and enabled until the corresponding link
has reached the network phase (i.e., LCP negotiation and authentication
have completed successfully) and the PPP node has been informed of
the link parameters via the
.Dv NGM_PPP_LINK_CONFIG
message.
.Pp
When a link is connected but disabled, all received frames are forwarded
directly out the
.Dv bypass
hook, and conversely, frames may be transmitted via the
.Dv bypass
hook as well.  This mode is appropriate for the link authentication phase.
As soon as the link is enabled, the PPP node will
begin processing frames received on the link.
.Sh COMPRESSION AND ENCRYPTION
Compression is supported via two hooks,
.Dv compress
and
.Dv decompress .
When enabled and connected, the PPP node writes outgoing frames on the
.Dv comp
hook and expects to receive back the compressed frame on the same hook.
Similarly, the
.Dv decompress
hook is used to uncompress incoming frames when decompression is
negotiated (compression and decompression are independently negotiable).
The type of node attached to these hooks should correspond
to the type of compression negotiated, e.g., Deflate, Predictor-1, etc.
.Pp
Encryption works exactly analogously via the
.Dv encrypt
and
.Dv decrypt
nodes.  Data is always compressed before being encrypted,
and decrypted before being decompressed.
.Pp
Only bundle-level compression and encryption is directly supported;
link-level compression and encryption can be handled transparently
by downstream nodes.
.Sh VAN JACOBSEN COMPRESSION
When all of the
.Dv vjc_ip ,
.Dv vjc_vjcomp ,
.Dv vjc_vjuncomp ,
and
.Dv vjc_vjip
hooks are connected, and the corresponding configuration flag is
enabled, Van Jacobsen compression and/or decompression will become active.
Normally these hooks connect to the corresponding hooks of a single
.Xr ng_vjc 8
node.  The PPP node is compatible with the
.Dq pass through
modes of the
.Xr ng_vjc 8
node type.
.Sh BYPASS HOOK
When a frame is received on a link with an unsupported protocol,
or a protocol which is disabled or for which the corresponding hook
is unconnected, the PPP node forwards the frame out the
.Dv bypass
hook, prepended with a four byte prefix.  This first two bytes of
the prefix indicate the link number on which the frame was received
(in network order).
For such frames received over the bundle (i.e., encapsulated in the
multi-link protocol), the special link number
.Dv NG_PPP_BUNDLE_LINKNUM
is used.  After the two byte link number is the two byte PPP protocol number
(also in network order).
The PPP protocol number is two bytes long even if the original frame
was protocol compressed.
.Pp
Conversely, any data written to the
.Dv bypass
hook is assumed to be in this same format.  The four byte header is
stripped off, the PPP protocol number is prepended (possibly compressed),
and the frame is delivered over the desired link.
If the link number is
.Dv NG_PPP_BUNDLE_LINKNUM
the frame will be delivered over the multi-link bundle; or, if multi-link
is disabled, over the (single) PPP link.
.Pp
Typically when the controlling entity receives a packet on the bypass
hook it responds either by dropping the frame (if it's not ready for
the protocol) or with an LCP protocol reject (if it doesn't recognize
or expect the protocol).
.Sh MULTILINK OPERATION
To enable multi-link PPP, the corresponding configuration flag must be set
and at least one link connected.  The PPP node will not allow more than
one link to be connected if multi-link is not enabled, nor will it allow
certain multi-link settings to be changed while multi-link operation is
active (e.g., short sequence number header format).
.Pp
Because packets are sent as fragments across multiple individual links,
it is important that when a link goes down the PPP node is notified
immediately, either by disconnecting the corresponding hook or disabling
the link via the
.Dv NGM_PPP_SET_CONFIG
control message.
.Pp
Each link has configuration parameters for latency (specified in
milliseconds) and bandwidth (specified in tens of bytes per second).
The PPP node can be configured for
.Em round-robin
or
.Em optimized
packet delivery.
.Pp
When configured for round-robin delivery, the latency and bandwidth
values are ignored and the PPP node simply sends each frame as a
single fragment, alternating frames across all the links in the
bundle.  This scheme has the advantage that even if one link fails
silently, some packets will still get through.  It has the disadvantage
of sub-optimal overall bundle latency, which is important for
interactive response time, and sub-optimal overall bundle bandwidth
when links with different bandwidths exist in the same bundle.
.Pp
When configured for optimal delivery, the PPP node distributes the
packet across the links in a way that minimizes the time it takes
for the completed packet to be received by the far end.  This
involves taking into account each link's latency, bandwidth, and
current queue length.  Therefore these numbers should be
configured as accurately as possible.  The algorithm does require
some computation, so may not be appropriate for very slow machines
and/or very fast links.
.Pp
As a special case, if all links have identical latency and bandwidth,
then the above algorithm is disabled (because it is unnecessary)
and the PPP node simply fragments frames into equal sized portions
across all of the links.
.Sh HOOKS
This node type supports the following hooks:
.Pp
.Bl -tag -compact -width vjc_vjuncomp
.It Dv link<N>
Individual PPP link number
.Dv <N>
.It Dv compress
Connection to compression engine
.It Dv decompress
Connection to decompression engine
.It Dv encrypt
Connection to encryption engine
.It Dv decrypt
Connection to decryption engine
.It Dv vjc_ip
Connection to
.Xr ng_vjc 8
.Dv ip
hook
.It Dv vjc_vjcomp
Connection to
.Xr ng_vjc 8
.Dv vjcomp
hook
.It Dv vjc_vjuncomp
Connection to
.Xr ng_vjc 8
.Dv vjuncomp
hook
.It Dv vjc_vjip
Connection to
.Xr ng_vjc 8
.Dv vjip
hook
.It Dv inet
IP packet data
.It Dv atalk
AppleTalk packet data
.It Dv ipx
IPX packet data
.It Dv bypass
Bypass hook; frames have a four byte header consisting of
a link number and a PPP protocol number.
.El
.Pp
.Sh CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
.Bl -tag -width foo
.It Dv NGM_PPP_SET_CONFIG
This command configures all aspects of the node.  This includes enabling
multi-link PPP, encryption, compression, Van Jacobsen compression, and IP,
AppleTalk, and IPX packet delivery.  It includes per-link configuration,
including enabling the link, setting latency and bandwidth parameters,
and enabling protocol field compression.  Note that no link or functionality
is active until the corresponding hook is also connected.
This command takes a
.Dv "struct ng_ppp_node_config"
as an argument:
.Bd -literal -offset 0
/* Per-link config structure */
struct ng_ppp_link_config {
  u_char    enableLink;     /* enable this link */
  u_char    enableProtoComp;/* enable protocol field compression */
  u_char    enableACFComp;  /* enable addr/ctrl field compression */
  u_int16_t mru;            /* peer MRU */
  u_int32_t latency;        /* link latency (in milliseconds) */
  u_int32_t bandwidth;      /* link bandwidth (in bytes/second) */
};

/* Node config structure */
struct ng_ppp_node_config {
  u_int16_t mrru;                   /* multilink peer MRRU */
  u_char    enableMultilink;        /* enable multilink */
  u_char    recvShortSeq;           /* recv multilink short seq # */
  u_char    xmitShortSeq;           /* xmit multilink short seq # */
  u_char    enableRoundRobin;       /* xmit whole packets */
  u_char    enableIP;               /* enable IP data flow */
  u_char    enableAtalk;            /* enable AppleTalk data flow */
  u_char    enableIPX;              /* enable IPX data flow */
  u_char    enableCompression;      /* enable PPP compression */
  u_char    enableDecompression;    /* enable PPP decompression */
  u_char    enableEncryption;       /* enable PPP encryption */
  u_char    enableDecryption;       /* enable PPP decryption */
  u_char    enableVJCompression;    /* enable VJ compression */
  u_char    enableVJDecompression;  /* enable VJ decompression */
  struct ng_ppp_link_config          /* per link config params */
            links[NG_PPP_MAX_LINKS];
};
.Ed
.Pp
.It Dv NGM_PPP_GET_CONFIG
Returns the current configuration as a
.Dv "struct ng_ppp_node_config" .
.It Dv NGM_PPP_GET_LINK_STATS
This command takes a two byte link number as an argument and returns a
.Dv "struct ng_ppp_link_stat"
containing statistics for the corresponding link.  Here
.Dv NG_PPP_BUNDLE_LINKNUM
is a valid link number corresponding to the multi-link bundle.
.It Dv NGM_PPP_CLR_LINK_STATS
This command takes a two byte link number as an argument and
clears the statistics for that link.
.It Dv NGM_PPP_GETCLR_LINK_STATS
Same as
.Dv NGM_PPP_GET_LINK_STATS ,
but also atomically clears the statistics as well.
.El
.Pp
This node type also accepts the control messages accepted by the
.Xr ng_vjc 8
node type. When received, these messages are simply forwarded to
the adjacent
.Xr ng_vjc 8
node, if any.  This is particularly useful when the individual
PPP links are able to generate
.Dv NGM_VJC_RECV_ERROR
messages (see
.Xr ng_vjc 8
for a description).
.Sh SHUTDOWN
This node shuts down upon receipt of a
.Dv NGM_SHUTDOWN
control message, or when all hooks have been disconnected.
.Sh SEE ALSO
.Xr netgraph 4 ,
.Xr ng_async 8 ,
.Xr ng_iface 8 ,
.Xr ng_vjc 8 ,
.Xr ng_pppoe 8 ,
.Xr ngctl 8 .
.Rs
.%A W. Simpson
.%T "The Point-to-Point Protocol (PPP)"
.%O RFC 1661
.Re
.Rs
.%A K. Sklower
.%A B. Lloyd
.%A G. McGregor
.%A D. Carr
.%A T. Coradetti
.%T "The PPP Multilink Protocol (MP)"
.%O RFC 1990
.Re
.Sh HISTORY
The
.Nm
node type was implemented in
.Fx 4.0 .
.Sh AUTHORS
.An Archie Cobbs Aq archie@whistle.com