sppp(4)

NAME

sppp - point to point protocol network layer for synchronous

lines

SYNOPSIS

device sppp

DESCRIPTION

The sppp network layer implements the state machine and the

Link Control
Protocol (LCP) of the point to point protocol (PPP) as de

scribed in RFC
1661. Note that this layer does not provide network inter

faces of its
own, it is rather intended to be layered on top of drivers

providing a
synchronous point-to-point connection that wish to run a PPP

stack over
it. The corresponding network interfaces have to be provid

ed by these
hardware drivers.

The sppp layer provides three basic modes of operation. The

default
mode, with no special flags to be set, is to create the PPP

connection
(administrative Open event to the LCP layer) as soon as the

interface is
taken up with the ifconfig(8) command. Taking the interface

down again
will terminate the LCP layer and thus all other layers on

top. The link
will also terminate itself as soon as no Network Control

Protocol (NCP)
is open anymore, indicating that the lower layers are no

longer needed.

Setting the link-level flag link0 with ifconfig(8) will

cause the respective network interface to go into passive mode. This means,

the administrative Open event to the LCP layer will be delayed until

after the lower
layers signals an Up event (rise of ``carrier''). This can

be used by
lower layers to support a dialin connection where the physi

cal layer is
not available immediately at startup, but only after some

external event
arrives. Receipt of a Down event from the lower layer will

not take the
interface completely down in this case.

Finally, setting the flag link1 will cause the interface to

operate in
dial-on-demand mode. This is also only useful if the lower

layer supports the notion of a carrier (like with an ISDN line). Up

on configuring
the respective interface, it will delay the administrative

Open event to
the LCP layer until either an outbound network packet ar

rives, or until
the lower layer signals an Up event, indicating an inbound

connection.
As with passive mode, receipt of a Down event (loss of car

rier) will not
automatically take the interface down, thus it remains

available for further connections.

The sppp layer supports the debug interface flag that can be

set with
ifconfig(8). If this flag is set, the various control pro

tocol packets
being exchanged as well as the option negotiation between

both ends of
the link will be logged at level LOG_DEBUG. This can be

helpful to examine configuration problems during the first attempts to set

up a new configuration. Without this flag being set, only the major

phase transitions will be logged at level LOG_INFO.

It is possible to leave the local interface IP address open

for negotiation by setting it to 0.0.0.0. This requires that the re

mote peer can
correctly supply a value for it based on the identity of the

caller, or
on the remote address supplied by this side. Due to the way

the IPCP
option negotiation works, this address is being supplied

late during the
negotiation, which might cause the remote peer to make wrong

assumptions.

In a similar spirit the remote address can be set to the

magical value
0.0.0.* which means that we do not care what address the re

mote side will
use, as long as it is not 0.0.0.0. This is useful if your

ISP has several dial-in servers. You can of course route add

something_or_other
0.0.0.* and it will do exactly what you would want it to.

The PAP and CHAP authentication protocols as described in

RFC 1334, and
RFC 1994 resp., are also implemented. Their parameters are

being controlled by the spppcontrol(8) utility.

VJ header compression is implemented, and enabled by de

fault. It can be
disabled using spppcontrol(8).

DIAGNOSTICS

<ifname><ifnum>: <proto> illegal <event> in state

<statename> An event
happened that should not happen for the current state the

respective control protocol is in. See RFC 1661 for a description of the

state automaton.

<ifname><ifnum>: loopback The state automaton detected a

line loopback
(that is, it was talking with itself). The interface will

be temporarily
disabled.

<ifname><ifnum>: up The LCP layer is running again, after a

line loopback had previously been detected.

<ifname><ifnum>: down The keepalive facility detected the

line being
unresponsive. Keepalive must be explicitly requested by the

lower layers
in order to take place.

SEE ALSO

inet(4), intro(4), ppp(4), ifconfig(8), spppcontrol(8)

W. Simpson, Editor, The Point-to-Point Protocol (PPP), RFC

1661.

G. McGregor, The PPP Internet Protocol Control Protocol

(IPCP), RFC 1332.

B. Lloyd and W. Simpson, PPP Authentication Protocols, RFC

1334.

W. Simpson, PPP Challenge Handshake Authentication Protocol

(CHAP), RFC
1994.

AUTHORS

The original implementation of sppp was written in 1994 at

Cronyx Ltd.,
Moscow by Serge Vakulenko <vak@cronyx.ru>. Jorg Wunsch
<joerg_wunsch@uriah.heep.sax.de> rewrote a large part in

1997 in order to
fully implement the state machine as described in RFC 1661,

so it could
also be used for dialup lines. He also wrote this man page.

Serge later
on wrote a basic implementation for PAP and CHAP, which

served as the
base for the current implementation, done again by Jorg Wun

sch.

BUGS

Many.

Currently, only the IPCP control protocol and ip(4) network

protocol is
supported. More NCPs should be implemented, as well as oth

er control
protocols for authentication and link quality reporting.

Negotiation loop avoidance is not fully implemented. If the

negotiation
does not converge, this can cause an endless loop.

The various parameters that should be adjustable per RFC

1661 are currently hard-coded into the kernel, and should be made acces

sible through
spppcontrol(8).

Passive mode has not been tested extensively.

Link-level compression protocols should be supported.

BSD December 30, 2001

BSD