184 lines
5.9 KiB
Groff
184 lines
5.9 KiB
Groff
.\" $NetBSD: pppoe.4,v 1.5 2002/01/14 13:46:53 wiz Exp $
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.\"
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.\" Copyright (c) 2001 Martin Husemann. 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 AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd December 10, 2001
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.Dt PPPOE 4
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.Os
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.Sh NAME
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.Nm pppoe
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.Nd PPP over Ethernet protocol network interface
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.Sh SYNOPSIS
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.Nm pseudo-device pppoe
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.Sh DESCRIPTION
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The
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.Nm
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interface encapsulatates
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.Em Point-to-Point Protocol (PPP)
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packets inside Ethernet frames as defined by
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.Li RFC2516 .
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.Pp
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This is often used to connect a router via a DSL modem to
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an access concentrator. The
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.Nm
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interface does not by itself transmit or receive frames,
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but needs an Ethernet interface to do so. This Ethernet interface
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is connected to the
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.Nm
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interface via
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.Xr pppoectl 8 .
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The Ethernet interface needs to be marked UP, but does not need to have an
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IP address.
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.Pp
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There are two basic modes of operation, controlled via the
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.Em link1
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switch. The default mode,
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.Em link1
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not being set, tries to keep the configured session open all the
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time. If the session is disconnected, a new connection attempt is started
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immediately. The
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.Dq dial on demand
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mode, selected by setting
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.Em link1 ,
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only establishes a connection when data is being sent to the interface.
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.Pp
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Before a
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.Nm
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interface is usable, it needs to be configured. The following steps
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are necessary:
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.Bl -bullet
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.It
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create the interface
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.It
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connect an Ethernet interface
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This interface is used for the physical communication. As noted above it
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must be marked UP, but need not have an IP address.
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.It
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configure authentication
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The PPP session needs to identify the client to the peer. For more details
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on the available options see
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.Xr pppoectl 8 .
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.El
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.Pp
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This all is typically accomplished using an
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.Pa /etc/ifconfig.pppoe0
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file.
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.Sh IMPORTANT NOTE
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If you are using a
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.Nm
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interface, you will have an unusual low MTU for todays internet.
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Combined with a lot of misconfigured sites (host using path MTU discovery
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behind a router blocking all ICMP traffic) this will often cause problems.
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Connections to this servers will only work, if your system advertizes the
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right MSS in the tcp three way handshake. To get the right MSS, you need
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to set
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.Bd -literal
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# Obey interface MTUs when calculationg MSS
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net.inet.tcp.mss_ifmtu=1
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.Ed
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.Pp
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in your
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.Pa /etc/sysctl.conf
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file.
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This causes the calculated MSS to be based on the MTU of the interface
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via which the packet is send. This is always the right value if you are
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sure the answer to this packet will be received on the same interface
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(I.e. you only have one interface connected to the internet.)
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.Pp
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Unfortunately this sysctl does not fix the MSS advertized by hosts in
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the network behind a
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.Nm
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connected router.
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.Sh EXAMPLES
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A typical
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.Pa /etc/ifconfig.pppoe0
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file looks like this:
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.Bd -literal
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create
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! /sbin/ifconfig ne0 up
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! /sbin/pppoectl -e ne0 $int
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! /sbin/pppoectl $int myauthproto=pap myauthname=testcaller myauthsecret=donttell
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inet 0.0.0.0 0.0.0.1
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#! /sbin/route add default -iface 0.0.0.1
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up
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.Ed
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The commented out call to
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.Xr route 8
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may be omitted and the route added in the ip-up script called by
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.Xr ifwatchd 8
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when the real IP address is known. This is easy in the
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.Dq connect always
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mode (link1 not set), but hard to acomplish in the
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.Dq dial on demand
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mode (link1 set). In the latter case adding an iface route is an easy
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workaround.
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.Pp
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The
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.Nm
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interfaces operate completely inside the kernel, without any userland
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support. Because of this, a special daemon is used to fire ip-up or
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down scripts to execute arbitrary code when the PPP session is established
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and addresses of the interface become available. To enable the usage of
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.Pa /etc/ppp/ip-up
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and
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.Pa /etc/ppp/ip-down
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for this purpose, simply add
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.Bd -literal
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ifwatchd=YES
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.Ed
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to
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.Pa /etc/rc.conf .
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See
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.Xr ifwatchd 8
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for details and parameters passed to these scripts.
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.Pp
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Since this is a PPP interface, the addresses assigned to the interface
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may change during PPP negotiation. There is no fine grained control available
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for deciding which addresses are acceptable and which are not. For the local
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side and the
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remote address there is exactly one choice: hard coded address or wildcard.
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If a real address is assigned to one side of the connection, PPP negotiation
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will only agree to exactly this address. If one side is wildcarded, every
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address suggested by the peer will be accepted.
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.Pp
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To wildcard the local address set it to 0.0.0.0, to wildcard the remote
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address set it to 0.0.0.1. Wildcarding is not available (nor necessary)
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for IPv6 operation.
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.Sh SEE ALSO
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.Xr ifwatchd 8 ,
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.Xr pppoectl 8
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.Rs
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.%R RFC
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.%N 2516
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.%D February 1999
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.%T "A Method for Transmitting PPP Over Ethernet (PPPoE)"
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.Re
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.Sh HISTORY
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The
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.Nm
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device appeared in
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.Nx 1.6 .
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.Sh BUGS
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This implementation is client side only.
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