pppoe



PPPOE(8)                                                              PPPOE(8)




NAME

       pppoe - user-space PPPoE client.


SYNOPSIS

       pppd pty pppoe [pppoe_options] [pppd_options]

       pppoe -A [pppoe_options]


DESCRIPTION

       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 ADSL service providers.



OPTIONS

       -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
              support!


       -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
              numbers  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-
              plain!


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



PPPOE BACKGROUND

       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.



DESIGN GOALS

       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
              standard.


       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.



NOTES

       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.



AUTHORS

       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/.



SEE ALSO

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




4th Berkeley Distribution         3 July 2000                         PPPOE(8)

Man(1) output converted with man2html