sppp - point to point protocol network layer for synchronous
pseudo-device sppp [count]
The sppp network layer implements the state machine and the
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
synchronous point-to-point connection that wish to run a PPP
it. The corresponding network interfaces have to be provided by these
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
taken up with the ifconfig(8) command. Taking the interface
will terminate the LCP layer and thus all other layers on
top. The link
will also terminate itself as soon as no Network Control
is open anymore, indicating that the lower layers are no
Setting the link-level flag link0 with ifconfig(8) will
cause the respective
network interface to go into passive mode. This means
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
take the interface completely down in this case.
Finally, setting the flag link1 will cause the interface to
dial-on-demand mode. This is also only useful if the lower
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
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
will be logged at level LOG_INFO.
It is possible to leave the local interface IP address open
by setting it to 0.0.0.0. This requires that the remote peer can
correctly supply a value for it based on the identity of the
on the remote address supplied by this side. Due to the way
the IPCP option
negotiation works, this address is being supplied late
negotiation, which might cause the remote peer to make wrong
In a similar spirit the remote address can be set to the
0.0.0.1 which means that we don't care what address the remote 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
0.0.0.1 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
by the spppcontrol(8) utility.
<ifname><ifnum>: <proto> illegal <event> in state
<statename> An event
happened that should not happen for the current state the
protocol is in. See RFC 1661 for a description of the
<ifname><ifnum>: loopback The state automaton detected a
(that is, it was talking with itself). The interface will
<ifname><ifnum>: up The LCP layer is running again, after a
had previously been detected.
<ifname><ifnum>: down The keepalive facility detected the
line being unresponsive.
Keepalive must be explicitly requested by the
in order to take place.
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
The original implementation of sppp was written in 1994 at
Moscow by Serge Vakulenko <email@example.com>. Joerg Wunsch
<firstname.lastname@example.org> 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.
on wrote a basic implementation for PAP and CHAP, which
served as the
base for the current implementation, done again by Joerg
Currently, only the IPCP control protocol and ip(4) network
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
authentication and link quality reporting.
IPCP should support VJ header compression.
Link-level compression protocols should be supported.
OpenBSD 3.6 May 19, 1997
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