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PPPOE(8)							      PPPOE(8)

       pppoe - user-space PPPoE client.

       pppd pty 'pppoe [pppoe_options]' [pppd_options]

       pppoe -A [pppoe_options]

       pppoe  is  a  user-space client for PPPoE (Point-to-Point Protocol over
       Ethernet) for Linux and other UNIX systems.   pppoe  works  in  concert
       with  the pppd PPP daemon to provide a PPP connection over Ethernet, as
       is used by many DSL service providers.

       -I interface
	      The -I option specifies the Ethernet interface  to  use.	 Under
	      Linux,  it  is  typically eth0 or eth1.  The interface should be
	      "up" before you start pppoe, but should  not  be	configured  to
	      have an IP address.

       -T timeout
	      The  -T  option  causes  pppoe  to exit if no session traffic is
	      detected for timeout seconds.  I recommend  that	you  use  this
	      option  as  an  extra  safety measure, but if you do, you should
	      make sure that PPP generates enough traffic so the timeout  will
	      normally	not  be	 triggered.  The best way to do this is to use
	      the lcp-echo-interval option to pppd.  You should set the	 PPPoE
	      timeout to be about four times the LCP echo interval.

       -D file_name
	      The  -D option causes every packet to be dumped to the specified
	      file_name.  This is intended for	debugging  only;  it  produces
	      huge amounts of output and greatly reduces performance.

       -V     The -V option causes pppoe to print its version number and exit.

       -A     The  -A option causes pppoe to send a PADI packet and then print
	      the names	 of  access  concentrators  in	each  PADO  packet  it
	      receives.	  Do not use this option in conjunction with pppd; the
	      -A option is meant to be used interactively to give  interesting
	      information about the access concentrator.

       -S service_name
	      Specifies	 the  desired  service name.  pppoe will only initiate
	      sessions with access concentrators which can provide the	speci‐
	      fied  service.   In  most	 cases,	 you  should  not specify this
	      option.  Use it only if you know that there are multiple	access
	      concentrators or know that you need a specific service name.

       -C ac_name
	      Specifies the desired access concentrator name.  pppoe will only
	      initiate sessions with the specified  access  concentrator.   In
	      most  cases, you should not specify this option.	Use it only if
	      you know that there are multiple access concentrators.  If  both
	      the  -S  and  -C options are specified, they must both match for
	      pppoe to initiate a session.

       -U     Causes pppoe to use the Host-Uniq tag in its discovery  packets.
	      This  lets  you  run multiple pppoe daemons without having their
	      discovery packets interfere with one another.  You  must	supply
	      this  option  to all pppoe daemons if you intend to run multiple
	      daemons simultaneously.

       -s     Causes pppoe to use synchronous PPP encapsulation.  If  you  use
	      this  option,  then you must use the sync option with pppd.  You
	      are encouraged to use  this  option  if  it  works,  because  it
	      greatly  reduces	the CPU overhead of pppoe.  However, it MAY be
	      unreliable on slow machines -- there is a race condition between
	      pppd  writing  data  and pppoe reading it.  For this reason, the
	      default setting is  asynchronous.	  If  you  encounter  bugs  or
	      crashes with Synchronous PPP, turn it off -- don't e-mail me for

       -m MSS Causes pppoe to clamp the TCP maximum segment size at the speci‐
	      fied value.  Because of PPPoE overhead, the maximum segment size
	      for PPPoE is smaller than	 for  normal  Ethernet	encapsulation.
	      This could cause problems for machines on a LAN behind a gateway
	      using PPPoE.  If you have a LAN behind a gateway, and the	 gate‐
	      way  connects to the Internet using PPPoE, you are strongly rec‐
	      ommended to use a -m 1412 option.	 This avoids having to set the
	      MTU on all the hosts on the LAN.

       -p file
	      Causes  pppoe  to	 write	its  process-ID to the specified file.
	      This can be used to locate and kill pppoe processes.

       -e sess:mac
	      Causes pppoe to skip the discovery phase and  move  directly  to
	      the  session  phase.   The  session is given by sess and the MAC
	      address of the peer by mac.  This mode is not meant  for	normal
	      use; it is designed only for pppoe-server(8).

       -n     Causes  pppoe  not to open a discovery socket.  This mode is not
	      meant for normal use; it is designed only for pppoe-server(8).

       -k     Causes pppoe to terminate an existing session by sending a  PADT
	      frame, and then exit.  You must use the -e option in conjunction
	      with this option to specify the session to kill.	 This  may  be
	      useful  for  killing sessions when a buggy peer does not realize
	      the session has ended.

       -d     Causes pppoe to perform discovery and then exit, after  printing
	      session information to standard output.  The session information
	      is printed in exactly the format	expected  by  the  -e  option.
	      This  option  lets  you initiate a PPPoE discovery, perform some
	      other work, and then start the actual PPP session.  Be  careful;
	      if  you use this option in a loop, you can create many sessions,
	      which may annoy your peer.

       -f disc:sess
	      The -f option sets the Ethernet frame types for PPPoE  discovery
	      and session frames.  The types are specified as hexadecimal num‐
	      bers separated by a colon.   Standard  PPPoE  uses  frame	 types
	      8863:8864.   You should not use this option unless you are abso‐
	      lutely sure the peer you	are  dealing  with  uses  non-standard
	      frame  types.   If  your ISP uses non-standard frame types, com‐

       -h     The -h option causes pppoe to print usage information and exit.

       PPPoE (Point-to-Point Protocol over Ethernet) is described in RFC  2516
       and is a protocol which allows the session abstraction to be maintained
       over bridged Ethernet networks.

       PPPoE works by encapsulating PPP frames in Ethernet frames.  The proto‐
       col has two distinct stages:  The discovery and the session stage.

       In  the	discovery  stage,  the	host  broadcasts a special PADI (PPPoE
       Active Discovery Initiation) frame to discover  any  access  concentra‐
       tors.   The access concentrators (typically, only one access concentra‐
       tor) reply with PADO (PPPoE Active Discovery Offer) packets, announcing
       their  presence and the services they offer.  The host picks one of the
       access concentrators and	 transmits  a  PADR  (PPPoE  Active  Discovery
       Request) packet, asking for a session.  The access concentrator replies
       with a PADS (PPPoE Active Discovery Session-Confirmation) packet.   The
       protocol then moves to the session stage.

       In  the	session	 stage,	 the host and access concentrator exchange PPP
       frames embedded in Ethernet frames.  The normal Ethernet	 MTU  is  1500
       bytes, but the PPPoE overhead plus two bytes of overhead for the encap‐
       sulated PPP frame mean that the MTU of the PPP  interface  is  at  most
       1492 bytes.  This causes all kinds of problems if you are using a Linux
       machine as a firewall and interfaces behind the firewall	 have  an  MTU
       greater than 1492.  In fact, to be safe, I recommend setting the MTU of
       machines behind the firewall to 1412, to allow for worst-case  TCP  and
       IP options in their respective headers.

       Normally,  PPP  uses the Link Control Protocol (LCP) to shut down a PPP
       link.  However, the PPPoE specification allows the link to be shut down
       with  a	special	 PADT (PPPoE Active Discovery Terminate) packet.  This
       client recognizes this packet and will correctly terminate if a	termi‐
       nate request is received for the PPP session.

       My  design  goals  for this PPPoE client were as follows, in descending
       order of importance:

       o      It must work.

       o      It must be a user-space program and not a kernel patch.

       o      The code must be easy to read and maintain.

       o      It must be fully compliant with RFC  2516,  the  proposed	 PPPoE

       o      It must never hang up forever -- if the connection is broken, it
	      must detect this and exit, allowing a wrapper script to  restart
	      the connection.

       o      It must be fairly efficient.

       I  believe  I have achieved all of these goals, but (of course) am open
       to suggestions, patches and ideas.  See my home page,  http://www.roar‐
       ingpenguin.com, for contact information.

       For  best  results,  you	 must give pppd an mtu option of 1492.	I have
       observed problems with  excessively-large  frames  unless  I  set  this
       option.	 Also, if pppoe is running on a firewall machine, all machines
       behind the firewall should have MTU's of 1412.

       If you have problems, check your system logs.  pppoe  logs  interesting
       things  to syslog.  You may have to turn on logging of debug-level mes‐
       sages for complete diagnosis.

       pppoe was written by David F. Skoll <dfs@roaringpenguin.com>, with much
       inspiration from an earlier version by Luke Stras.

       The pppoe home page is http://www.roaringpenguin.com/pppoe/.

       pppoe-start(8),	    pppoe-stop(8),	pppoe-connect(8),     pppd(8),
       pppoe.conf(5), pppoe-setup(8), pppoe-status(8), pppoe-sniff(8),	pppoe-
       server(8), pppoe-relay(8)

4th Berkeley Distribution	  3 July 2000			      PPPOE(8)

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