1PPPOE(8) System Manager's Manual PPPOE(8)
2
6 pppoe - user-space PPPoE client.
7
9 pppd pty 'pppoe [pppoe_options]' [pppd_options]
10 pppoe -A [pppoe_options]
12
14 pppoe is a user-space client for PPPoE (Point-to-Point Protocol over
15 Ethernet) for Linux and other UNIX systems. pppoe works in concert
16 with the pppd PPP daemon to provide a PPP connection over Ethernet, as
17 is used by many DSL service providers.
18
21 -I interface
22 The -I option specifies the Ethernet interface to use. Under
23 Linux, it is typically eth0 or eth1. The interface should be
24 "up" before you start pppoe, but should not be configured to
25 have an IP address.
26 -T timeout
29 The -T option causes pppoe to exit if no session traffic is
30 detected for timeout seconds. I recommend that you use this
31 option as an extra safety measure, but if you do, you should
32 make sure that PPP generates enough traffic so the timeout will
33 normally not be triggered. The best way to do this is to use
34 the lcp-echo-interval option to pppd. You should set the PPPoE
35 timeout to be about four times the LCP echo interval.
36 -D file_name
39 The -D option causes every packet to be dumped to the specified
40 file_name. This is intended for debugging only; it produces
41 huge amounts of output and greatly reduces performance.
42 -V The -V option causes pppoe to print its version number and exit.
45 -A The -A option causes pppoe to send a PADI packet and then print
48 the names of access concentrators in each PADO packet it
49 receives. Do not use this option in conjunction with pppd; the
50 -A option is meant to be used interactively to give interesting
51 information about the access concentrator.
52 -S service_name
55 Specifies the desired service name. pppoe will only initiate
56 sessions with access concentrators which can provide the speci‐
57 fied service. In most cases, you should not specify this
58 option. Use it only if you know that there are multiple access
59 concentrators or know that you need a specific service name.
60 -C ac_name
63 Specifies the desired access concentrator name. pppoe will only
64 initiate sessions with the specified access concentrator. In
65 most cases, you should not specify this option. Use it only if
66 you know that there are multiple access concentrators. If both
67 the -S and -C options are specified, they must both match for
68 pppoe to initiate a session.
69 -U Causes pppoe to use the Host-Uniq tag in its discovery packets.
72 This lets you run multiple pppoe daemons without having their
73 discovery packets interfere with one another. You must supply
74 this option to all pppoe daemons if you intend to run multiple
75 daemons simultaneously.
76 -s Causes pppoe to use synchronous PPP encapsulation. If you use
79 this option, then you must use the sync option with pppd. You
80 are encouraged to use this option if it works, because it
81 greatly reduces the CPU overhead of pppoe. However, it MAY be
82 unreliable on slow machines -- there is a race condition between
83 pppd writing data and pppoe reading it. For this reason, the
84 default setting is asynchronous. If you encounter bugs or
85 crashes with Synchronous PPP, turn it off -- don't e-mail me for
86 support!
87 -m MSS Causes pppoe to clamp the TCP maximum segment size at the speci‐
90 fied value. Because of PPPoE overhead, the maximum segment size
91 for PPPoE is smaller than for normal Ethernet encapsulation.
92 This could cause problems for machines on a LAN behind a gateway
93 using PPPoE. If you have a LAN behind a gateway, and the gate‐
94 way connects to the Internet using PPPoE, you are strongly rec‐
95 ommended to use a -m 1412 option. This avoids having to set the
96 MTU on all the hosts on the LAN.
97 -p file
100 Causes pppoe to write its process-ID to the specified file.
101 This can be used to locate and kill pppoe processes.
102 -e sess:mac
105 Causes pppoe to skip the discovery phase and move directly to
106 the session phase. The session is given by sess and the MAC
107 address of the peer by mac. This mode is not meant for normal
108 use; it is designed only for pppoe-server(8).
109 -n Causes pppoe not to open a discovery socket. This mode is not
112 meant for normal use; it is designed only for pppoe-server(8).
113 -k Causes pppoe to terminate an existing session by sending a PADT
116 frame, and then exit. You must use the -e option in conjunction
117 with this option to specify the session to kill. This may be
118 useful for killing sessions when a buggy peer does not realize
119 the session has ended.
120 -d Causes pppoe to perform discovery and then exit, after printing
123 session information to standard output. The session information
124 is printed in exactly the format expected by the -e option.
125 This option lets you initiate a PPPoE discovery, perform some
126 other work, and then start the actual PPP session. Be careful;
127 if you use this option in a loop, you can create many sessions,
128 which may annoy your peer.
129 -f disc:sess
132 The -f option sets the Ethernet frame types for PPPoE discovery
133 and session frames. The types are specified as hexadecimal num‐
134 bers separated by a colon. Standard PPPoE uses frame types
135 8863:8864. You should not use this option unless you are abso‐
136 lutely sure the peer you are dealing with uses non-standard
137 frame types. If your ISP uses non-standard frame types, com‐
138 plain!
139 -h The -h option causes pppoe to print usage information and exit.
142
145 PPPoE (Point-to-Point Protocol over Ethernet) is described in RFC 2516
146 and is a protocol which allows the session abstraction to be maintained
147 over bridged Ethernet networks.
148 PPPoE works by encapsulating PPP frames in Ethernet frames. The proto‐
150 col has two distinct stages: The discovery and the session stage.
151 In the discovery stage, the host broadcasts a special PADI (PPPoE
153 Active Discovery Initiation) frame to discover any access concentra‐
154 tors. The access concentrators (typically, only one access concentra‐
155 tor) reply with PADO (PPPoE Active Discovery Offer) packets, announcing
156 their presence and the services they offer. The host picks one of the
157 access concentrators and transmits a PADR (PPPoE Active Discovery
158 Request) packet, asking for a session. The access concentrator replies
159 with a PADS (PPPoE Active Discovery Session-Confirmation) packet. The
160 protocol then moves to the session stage.
161 In the session stage, the host and access concentrator exchange PPP
163 frames embedded in Ethernet frames. The normal Ethernet MTU is 1500
164 bytes, but the PPPoE overhead plus two bytes of overhead for the encap‐
165 sulated PPP frame mean that the MTU of the PPP interface is at most
166 1492 bytes. This causes all kinds of problems if you are using a Linux
167 machine as a firewall and interfaces behind the firewall have an MTU
168 greater than 1492. In fact, to be safe, I recommend setting the MTU of
169 machines behind the firewall to 1412, to allow for worst-case TCP and
170 IP options in their respective headers.
171 Normally, PPP uses the Link Control Protocol (LCP) to shut down a PPP
173 link. However, the PPPoE specification allows the link to be shut down
174 with a special PADT (PPPoE Active Discovery Terminate) packet. This
175 client recognizes this packet and will correctly terminate if a termi‐
176 nate request is received for the PPP session.
177
180 My design goals for this PPPoE client were as follows, in descending
181 order of importance:
182 o It must work.
185 o It must be a user-space program and not a kernel patch.
188 o The code must be easy to read and maintain.
191 o It must be fully compliant with RFC 2516, the proposed PPPoE
194 standard.
195 o It must never hang up forever -- if the connection is broken, it
198 must detect this and exit, allowing a wrapper script to restart
199 the connection.
200 o It must be fairly efficient.
203 I believe I have achieved all of these goals, but (of course) am open
206 to suggestions, patches and ideas. See my home page, http://www.roar‐
207 ingpenguin.com, for contact information.
208
211 For best results, you must give pppd an mtu option of 1492. I have
212 observed problems with excessively-large frames unless I set this
213 option. Also, if pppoe is running on a firewall machine, all machines
214 behind the firewall should have MTU's of 1412.
215 If you have problems, check your system logs. pppoe logs interesting
217 things to syslog. You may have to turn on logging of debug-level mes‐
218 sages for complete diagnosis.
219
222 pppoe was written by David F. Skoll <dfs@roaringpenguin.com>, with much
223 inspiration from an earlier version by Luke Stras.
224 The pppoe home page is http://www.roaringpenguin.com/pppoe/.
226
229 pppoe-start(8), pppoe-stop(8), pppoe-connect(8), pppd(8),
230 pppoe.conf(5), pppoe-setup(8), pppoe-status(8), pppoe-sniff(8), pppoe-
231 server(8), pppoe-relay(8)
2324th Berkeley Distribution 3 July 2000 PPPOE(8)