.\"
.\" Copyright (c) 1997, 2002 Hellmuth Michaelis. All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" $FreeBSD$
.\"
.\"	last edit-date: [Sun Jul 28 14:29:08 2002]
.\"
.Dd July 28, 2002
.Dt I4BIPR 4
.Os
.Sh NAME
.Nm i4bipr
.Nd isdn4bsd IP over ISDN B-channel network driver
.Sh SYNOPSIS
.Cd device \&"i4bipr\&" Op count
.Sh DESCRIPTION
The
.Nm
driver interfaces the IP subsystem of the operating system with the
isdn4bsd package so that transport of IP packets over an ISDN link
is possible.
.Pp
The driver just packs IP packets without anything appended or prepended
into raw HDLC packets on the B channel and transfers them to a remote site.
IP packets received from the remote site are queued into the local IP
protocol stack.
.Pp
The format of the resulting packet on the B channel is:
.Pp
.Dl (HDLC opening flag) (IP-packet) (CRC) (HDLC closing flag)
.Pp
In the case where an IP packet for a remote site arrives in the driver and no
connection has been established yet, the driver communicates with the
.Xr isdnd 8
daemon to establish a connection.
.Pp
The driver has support for interfacing to the
.Xr bpf 4
subsystem for using
.Xr tcpdump 1
with the
.Nm ipr
interfaces.
.Pp
The driver optionally (when compiled with the IPR_VJ option) provides Van
Jacobsen header compression, under control of the link0 and link1 options to
.Xr ifconfig 8 :
.Pp
.Bl -tag -width 15n -offset indent -compact
.It link0
Apply VJ compression to outgoing packets on this interface, and assume that
incoming packets require decompression.
.It link1
Check incoming packets for Van Jacobsen compression; if they appear to be
compressed, automatically set link0.
.El
.Pp
The default values are
.Em on
for
.Em link1
and
.Em off
for
.Em link0 .
.Sh SEE ALSO
.Xr tcpdump 1 ,
.Xr bpf 4 ,
.Xr isdnd.rc 5 ,
.Xr isdnd 8
.Sh AUTHORS
The
.Nm
device driver and this manpage were written by
.An Hellmuth Michaelis Aq hm@FreeBSD.org .