1PPPOE(8) System Manager's Manual PPPOE(8)
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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 -t timeout
39 The -t option sets the initial timeout for discovery packets in
40 seconds.
41 -D file_name
44 The -D option causes every packet to be dumped to the specified
45 file_name. This is intended for debugging only; it produces
46 huge amounts of output and greatly reduces performance.
47 -V The -V option causes pppoe to print its version number and exit.
50 -A The -A option causes pppoe to send a PADI packet and then print
53 the names of access concentrators in each PADO packet it
54 receives. Do not use this option in conjunction with pppd; the
55 -A option is meant to be used interactively to give interesting
56 information about the access concentrator.
57 -S service_name
60 Specifies the desired service name. pppoe will only initiate
61 sessions with access concentrators which can provide the speci‐
62 fied service. In most cases, you should not specify this
63 option. Use it only if you know that there are multiple access
64 concentrators or know that you need a specific service name.
65 -C ac_name
68 Specifies the desired access concentrator name. pppoe will only
69 initiate sessions with the specified access concentrator. In
70 most cases, you should not specify this option. Use it only if
71 you know that there are multiple access concentrators. If both
72 the -S and -C options are specified, they must both match for
73 pppoe to initiate a session.
74 -U Causes pppoe to use the Host-Uniq tag in its discovery packets.
77 This lets you run multiple pppoe daemons without having their
78 discovery packets interfere with one another. You must supply
79 this option to all pppoe daemons if you intend to run multiple
80 daemons simultaneously. The specific Host-Uniq value used is
81 the hexadecimal representation of the pppoe process's PID.
82 -W value
85 Causes pppoe to use the Host-Uniq tag in its discovery packets,
86 and furthermore to set the value of Host-Uniq to value. Use
87 with caution. Note that -W and -U are mutually-incompatible.
88 -s Causes pppoe to use synchronous PPP encapsulation. If you use
91 this option, then you must use the sync option with pppd. You
92 are encouraged to use this option if it works, because it
93 greatly reduces the CPU overhead of pppoe. However, it MAY be
94 unreliable on slow machines -- there is a race condition between
95 pppd writing data and pppoe reading it. For this reason, the
96 default setting is asynchronous. If you encounter bugs or
97 crashes with Synchronous PPP, turn it off -- don't e-mail me for
98 support!
99 -m MSS Causes pppoe to clamp the TCP maximum segment size at the speci‐
102 fied value. Because of PPPoE overhead, the maximum segment size
103 for PPPoE is smaller than for normal Ethernet encapsulation.
104 This could cause problems for machines on a LAN behind a gateway
105 using PPPoE. If you have a LAN behind a gateway, and the gate‐
106 way connects to the Internet using PPPoE, you are strongly rec‐
107 ommended to use a -m 1412 option. This avoids having to set the
108 MTU on all the hosts on the LAN.
109 -p file
112 Causes pppoe to write its process-ID to the specified file.
113 This can be used to locate and kill pppoe processes.
114 -e sess:mac
117 Causes pppoe to skip the discovery phase and move directly to
118 the session phase. The session is given by sess and the MAC
119 address of the peer by mac. This mode is not meant for normal
120 use; it is designed only for pppoe-server(8).
121 -n Causes pppoe not to open a discovery socket. This mode is not
124 meant for normal use; it is designed only for pppoe-server(8).
125 -k Causes pppoe to terminate an existing session by sending a PADT
128 frame, and then exit. You must use the -e option in conjunction
129 with this option to specify the session to kill. This may be
130 useful for killing sessions when a buggy peer does not realize
131 the session has ended.
132 -d Causes pppoe to perform discovery and then exit, after printing
135 session information to standard output. The session information
136 is printed in exactly the format expected by the -e option.
137 This option lets you initiate a PPPoE discovery, perform some
138 other work, and then start the actual PPP session. Be careful;
139 if you use this option in a loop, you can create many sessions,
140 which may annoy your peer.
141 -f disc:sess
144 The -f option sets the Ethernet frame types for PPPoE discovery
145 and session frames. The types are specified as hexadecimal num‐
146 bers separated by a colon. Standard PPPoE uses frame types
147 8863:8864. You should not use this option unless you are abso‐
148 lutely sure the peer you are dealing with uses non-standard
149 frame types. If your ISP uses non-standard frame types, com‐
150 plain!
151 -F numfloods
154 The -F option sets the discovery flood, only used for stress-
155 testing.
156 -h The -h option causes pppoe to print usage information and exit.
159
162 PPPoE (Point-to-Point Protocol over Ethernet) is described in RFC 2516
163 and is a protocol which allows the session abstraction to be maintained
164 over bridged Ethernet networks.
165 PPPoE works by encapsulating PPP frames in Ethernet frames. The proto‐
167 col has two distinct stages: The discovery and the session stage.
168 In the discovery stage, the host broadcasts a special PADI (PPPoE
170 Active Discovery Initiation) frame to discover any access concentra‐
171 tors. The access concentrators (typically, only one access concentra‐
172 tor) reply with PADO (PPPoE Active Discovery Offer) packets, announcing
173 their presence and the services they offer. The host picks one of the
174 access concentrators and transmits a PADR (PPPoE Active Discovery
175 Request) packet, asking for a session. The access concentrator replies
176 with a PADS (PPPoE Active Discovery Session-Confirmation) packet. The
177 protocol then moves to the session stage.
178 In the session stage, the host and access concentrator exchange PPP
180 frames embedded in Ethernet frames. The normal Ethernet MTU is 1500
181 bytes, but the PPPoE overhead plus two bytes of overhead for the encap‐
182 sulated PPP frame mean that the MTU of the PPP interface is at most
183 1492 bytes. This causes all kinds of problems if you are using a Linux
184 machine as a firewall and interfaces behind the firewall have an MTU
185 greater than 1492. In fact, to be safe, I recommend setting the MTU of
186 machines behind the firewall to 1412, to allow for worst-case TCP and
187 IP options in their respective headers.
188 Normally, PPP uses the Link Control Protocol (LCP) to shut down a PPP
190 link. However, the PPPoE specification allows the link to be shut down
191 with a special PADT (PPPoE Active Discovery Terminate) packet. This
192 client recognizes this packet and will correctly terminate if a termi‐
193 nate request is received for the PPP session.
194
197 My design goals for this PPPoE client were as follows, in descending
198 order of importance:
199 o It must work.
202 o It must be a user-space program and not a kernel patch.
205 o The code must be easy to read and maintain.
208 o It must be fully compliant with RFC 2516, the proposed PPPoE
211 standard.
212 o It must never hang up forever -- if the connection is broken, it
215 must detect this and exit, allowing a wrapper script to restart
216 the connection.
217 o It must be fairly efficient.
220 I believe I have achieved all of these goals, but (of course) am open
223 to suggestions, patches and ideas. See my home page,
224 https://dianne.skoll.ca/projects/rp-pppoe/, for contact information.
225
228 For best results, you must give pppd an mtu option of 1492. I have
229 observed problems with excessively-large frames unless I set this
230 option. Also, if pppoe is running on a firewall machine, all machines
231 behind the firewall should have MTU's of 1412.
232 If you have problems, check your system logs. pppoe logs interesting
234 things to syslog. You may have to turn on logging of debug-level mes‐
235 sages for complete diagnosis.
236
239 pppoe was written by Dianne Skoll <dianne@skoll.ca>, with much inspira‐
240 tion from an earlier version by Luke Stras.
241 The pppoe home page is https://dianne.skoll.ca/projects/rp-pppoe/.
243
246 pppoe-start(8), pppoe-stop(8), pppoe-connect(8), pppd(8),
247 pppoe.conf(5), pppoe-setup(8), pppoe-status(8), pppoe-sniff(8), pppoe-
248 server(8), pppoe-relay(8)
2494th Berkeley Distribution 5 October 2015 PPPOE(8)