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NAME    [Toc]    [Back]

     sppp - point to point protocol network layer for synchronous

SYNOPSIS    [Toc]    [Back]

     pseudo-device sppp [count]

DESCRIPTION    [Toc]    [Back]

     The  sppp network layer implements the state machine and the
Link Control
     Protocol (LCP) of the point to point protocol (PPP)  as  described in RFC
     1661.   Note that this layer does not provide network interfaces 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 provided by these
     hardware drivers.

     The sppp layer provides three basic modes of operation.  The
     mode, with no special flags to be set, is to create the  PPP
     (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 dial-in connection where the physical layer
     isn't  available immediately at startup, but only after some
     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).  Upon configuring
     the respective interface, it will delay  the  administrative
Open event to
     the  LCP  layer  until either an outbound network packet arrives, or until
     the lower layer signals an Up event, indicating  an  inbound
     As  with passive mode, receipt of a Down event (loss of carrier) will not
     automatically take  the  interface  down,  thus  it  remains
available for further

     The sppp layer supports the debug interface flag that can be
set with
     ifconfig(8).  If this flag is set, the various control  protocol 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  This requires that  the  remote 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

     In  a  similar  spirit  the remote address can be set to the
magical value which means that we don't care what address the  remote side will
     use,  as  long as it is not  This is useful if your
ISP has several
 dial-in servers.  You can of course route  add  something
or other 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.

DIAGNOSTICS    [Toc]    [Back]

     <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

     <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    [Toc]    [Back]

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

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

     G. McGregor, The  PPP  Internet  Protocol  Control  Protocol
(IPCP), RFC 1332.

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

     W. Simpson, PPP Challenge Handshake Authentication  Protocol

AUTHORS    [Toc]    [Back]

     The  original  implementation of sppp was written in 1994 at
Cronyx Ltd.,
     Moscow by Serge Vakulenko <vak@cronyx.ru>.  Joerg 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  Joerg

BUGS    [Toc]    [Back]


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

     Negotiation loop avoidance is not fully implemented.  If the
     doesn't 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 accessible through

     Passive mode has not been tested extensively.

     More  NCPs  should  be implemented, as well as other control
protocols for
     authentication and link quality reporting.

     IPCP should support VJ header compression.

     Link-level compression protocols should be supported.

OpenBSD      3.6                           May      19,      1997
[ Back ]
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