239 lines
7.3 KiB
Groff
239 lines
7.3 KiB
Groff
.\"
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.\" Copyright (c) 1997, 2001 Joerg Wunsch
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.\"
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 25, 2008
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.Dt SPPP 4
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.Os
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.Sh NAME
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.Nm sppp
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.Nd point to point protocol network layer for synchronous lines
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.Sh SYNOPSIS
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.Cd "device sppp"
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.Sh DESCRIPTION
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The
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.Nm
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network layer implements the state machine and the Link Control
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Protocol (LCP) of the
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.Em point to point protocol (PPP)
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as described in RFC 1661.
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Note that this layer does not provide
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network interfaces of its own, it is rather intended to be layered on
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top of drivers providing a synchronous point-to-point connection that
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wish to run a PPP stack over it.
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The corresponding network interfaces
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have to be provided by these hardware drivers.
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.Pp
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The
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.Nm
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layer provides three basic modes of operation.
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The default mode,
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with no special flags to be set, is to create the PPP connection
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(administrative
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.Em Open
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event to the LCP layer) as soon as the interface is taken up with the
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.Xr ifconfig 8
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command.
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Taking the interface down again will terminate the LCP layer
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and thus all other layers on top.
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The link will also terminate itself as
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soon as no Network Control Protocol (NCP) is open anymore, indicating
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that the lower layers are no longer needed.
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.Pp
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Setting the link-level flag
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.Em link0
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with
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.Xr ifconfig 8
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will cause the respective network interface to go into
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.Em passive
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mode.
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This means, the administrative
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.Em Open
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event to the LCP layer will be delayed until after the lower layers
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signals an
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.Em Up
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event (rise of
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.Dq carrier ) .
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This can be used by lower layers to support
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a dialin connection where the physical layer is not available
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immediately at startup, but only after some external event arrives.
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Receipt of a
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.Em Down
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event from the lower layer will not take the interface completely down
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in this case.
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.Pp
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Finally, setting the flag
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.Em link1
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will cause the interface to operate in
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.Em dial-on-demand
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mode.
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This is also only useful if the lower layer supports the notion
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of a carrier.
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Upon configuring the
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respective interface, it will delay the administrative
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.Em Open
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event to the LCP layer until either an outbound network packet
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arrives, or until the lower layer signals an
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.Em Up
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event, indicating an inbound connection.
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As with passive mode, receipt
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of a
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.Em Down
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event (loss of carrier) will not automatically take the interface down,
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thus it remains available for further connections.
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.Pp
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The
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.Nm
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layer supports the
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.Em debug
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interface flag that can be set with
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.Xr ifconfig 8 .
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If this flag is set, the various control protocol packets being
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exchanged as well as the option negotiation between both ends of the
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link will be logged at level
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.Dv LOG_DEBUG .
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This can be helpful to examine configuration problems during the first
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attempts to set up a new configuration.
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Without this flag being set,
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only the major phase transitions will be logged at level
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.Dv LOG_INFO .
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.Pp
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It is possible to leave the local interface IP address open for
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negotiation by setting it to 0.0.0.0.
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This requires that the remote
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peer can correctly supply a value for it based on the identity of the
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caller, or on the remote address supplied by this side.
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Due to the
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way the IPCP option negotiation works, this address is being supplied
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late during the negotiation, which might cause the remote peer to make
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wrong assumptions.
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.Pp
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In a similar spirit the remote address can be set to the magical
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value
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.Li 0.0.0. Ns Em *
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which means that we do not care what address the remote
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side will use, as long as it is not 0.0.0.0.
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This is useful if your ISP has several dial-in
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servers.
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You can of course
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.Nm route Cm add Ar something_or_other 0.0.0. Ns Em *
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and it will do exactly what you would want it to.
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.Pp
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The PAP and CHAP authentication protocols as described in RFC 1334,
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and RFC 1994 resp., are also implemented.
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Their parameters are being
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controlled by the
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.Xr spppcontrol 8
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utility.
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.Pp
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VJ header compression is implemented, and enabled by default.
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It can be
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disabled using
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.Xr spppcontrol 8 .
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.Sh DIAGNOSTICS
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.Bl -diag
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.It <ifname><ifnum>: <proto> illegal <event> in state <statename>
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An event happened that should not happen for the current state
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the respective control protocol is in.
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See RFC 1661 for a description
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of the state automaton.
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.It <ifname><ifnum>: loopback
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The state automaton detected a line loopback (that is, it was talking
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with itself).
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The interface will be temporarily disabled.
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.It <ifname><ifnum>: up
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The LCP layer is running again, after a line loopback had previously
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been detected.
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.It <ifname><ifnum>: down
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The keepalive facility detected the line being unresponsive.
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Keepalive must be explicitly requested by the lower layers in order to
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take place.
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.El
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.Sh SEE ALSO
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.Xr inet 4 ,
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.Xr intro 4 ,
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.Xr ifconfig 8 ,
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.Xr spppcontrol 8
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.Rs
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.%A W. Simpson, Editor
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.%T "The Point-to-Point Protocol (PPP)"
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.%O RFC 1661
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.Re
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.Rs
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.%A G. McGregor
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.%T "The PPP Internet Protocol Control Protocol (IPCP)"
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.%O RFC 1332
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.Re
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.Rs
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.%A B. Lloyd
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.%A W. Simpson
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.%T "PPP Authentication Protocols"
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.%O RFC 1334
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.Re
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.Rs
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.%A W. Simpson
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.%T "PPP Challenge Handshake Authentication Protocol (CHAP)"
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.%O RFC 1994
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.Re
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.Sh AUTHORS
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.An -nosplit
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The original implementation of
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.Nm
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was written in 1994 at Cronyx Ltd., Moscow by
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.An Serge Vakulenko Aq Mt vak@cronyx.ru .
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.An J\(:org Wunsch Aq Mt joerg_wunsch@uriah.heep.sax.de
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rewrote a large part in 1997 in order
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to fully implement the state machine as described in RFC 1661, so it
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could also be used for dialup lines.
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He also wrote this man page.
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Serge later on wrote a basic implementation for PAP and CHAP, which
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served as the base for the current implementation, done again by
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.An J\(:org Wunsch .
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.Sh BUGS
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Many.
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.Pp
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Currently, only the
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.Em IPCP
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control protocol and
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.Xr ip 4
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network protocol is supported.
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More NCPs should be implemented, as well as other control protocols
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for authentication and link quality reporting.
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.Pp
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Negotiation loop avoidance is not fully implemented.
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If the negotiation
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does not converge, this can cause an endless loop.
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.Pp
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The various parameters that should be adjustable per RFC 1661 are
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currently hard-coded into the kernel, and should be made accessible
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through
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.Xr spppcontrol 8 .
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.Pp
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.Em Passive
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mode has not been tested extensively.
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.Pp
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Link-level compression protocols should be supported.
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