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.
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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 de‐
30 tected for timeout seconds. I recommend that you use this op‐
31 tion as an extra safety measure, but if you do, you should make
32 sure that PPP generates enough traffic so the timeout will nor‐
33 mally not be triggered. The best way to do this is to use the
34 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 re‐
49 ceives. Do not use this option in conjunction with pppd; the -A
50 option is meant to be used interactively to give interesting in‐
51 formation 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 op‐
58 tion. 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. The specific Host-Uniq value used is
76 the hexadecimal representation of the pppoe process's PID.
77 -W value
80 Causes pppoe to use the Host-Uniq tag in its discovery packets,
81 and furthermore to set the value of Host-Uniq to value. Use
82 with caution. Note that -W and -U are mutually-incompatible.
83 -s Causes pppoe to use synchronous PPP encapsulation. If you use
86 this option, then you must use the sync option with pppd. You
87 are encouraged to use this option if it works, because it
88 greatly reduces the CPU overhead of pppoe. However, it MAY be
89 unreliable on slow machines -- there is a race condition between
90 pppd writing data and pppoe reading it. For this reason, the
91 default setting is asynchronous. If you encounter bugs or
92 crashes with Synchronous PPP, turn it off -- don't e-mail me for
93 support!
94 -m MSS Causes pppoe to clamp the TCP maximum segment size at the speci‐
97 fied value. Because of PPPoE overhead, the maximum segment size
98 for PPPoE is smaller than for normal Ethernet encapsulation.
99 This could cause problems for machines on a LAN behind a gateway
100 using PPPoE. If you have a LAN behind a gateway, and the gate‐
101 way connects to the Internet using PPPoE, you are strongly rec‐
102 ommended to use a -m 1412 option. This avoids having to set the
103 MTU on all the hosts on the LAN.
104 -p file
107 Causes pppoe to write its process-ID to the specified file.
108 This can be used to locate and kill pppoe processes.
109 -e sess:mac
112 Causes pppoe to skip the discovery phase and move directly to
113 the session phase. The session is given by sess and the MAC ad‐
114 dress of the peer by mac. This mode is not meant for normal
115 use; it is designed only for pppoe-server(8).
116 -n Causes pppoe not to open a discovery socket. This mode is not
119 meant for normal use; it is designed only for pppoe-server(8).
120 -k Causes pppoe to terminate an existing session by sending a PADT
123 frame, and then exit. You must use the -e option in conjunction
124 with this option to specify the session to kill. This may be
125 useful for killing sessions when a buggy peer does not realize
126 the session has ended.
127 -d Causes pppoe to perform discovery and then exit, after printing
130 session information to standard output. The session information
131 is printed in exactly the format expected by the -e option.
132 This option lets you initiate a PPPoE discovery, perform some
133 other work, and then start the actual PPP session. Be careful;
134 if you use this option in a loop, you can create many sessions,
135 which may annoy your peer.
136 -f disc:sess
139 The -f option sets the Ethernet frame types for PPPoE discovery
140 and session frames. The types are specified as hexadecimal num‐
141 bers separated by a colon. Standard PPPoE uses frame types
142 8863:8864. You should not use this option unless you are abso‐
143 lutely sure the peer you are dealing with uses non-standard
144 frame types. If your ISP uses non-standard frame types, com‐
145 plain!
146 -h The -h option causes pppoe to print usage information and exit.
149
152 PPPoE (Point-to-Point Protocol over Ethernet) is described in RFC 2516
153 and is a protocol which allows the session abstraction to be maintained
154 over bridged Ethernet networks.
155 PPPoE works by encapsulating PPP frames in Ethernet frames. The proto‐
157 col has two distinct stages: The discovery and the session stage.
158 In the discovery stage, the host broadcasts a special PADI (PPPoE Ac‐
160 tive Discovery Initiation) frame to discover any access concentrators.
161 The access concentrators (typically, only one access concentrator) re‐
162 ply with PADO (PPPoE Active Discovery Offer) packets, announcing their
163 presence and the services they offer. The host picks one of the access
164 concentrators and transmits a PADR (PPPoE Active Discovery Request)
165 packet, asking for a session. The access concentrator replies with a
166 PADS (PPPoE Active Discovery Session-Confirmation) packet. The proto‐
167 col then moves to the session stage.
168 In the session stage, the host and access concentrator exchange PPP
170 frames embedded in Ethernet frames. The normal Ethernet MTU is 1500
171 bytes, but the PPPoE overhead plus two bytes of overhead for the encap‐
172 sulated PPP frame mean that the MTU of the PPP interface is at most
173 1492 bytes. This causes all kinds of problems if you are using a Linux
174 machine as a firewall and interfaces behind the firewall have an MTU
175 greater than 1492. In fact, to be safe, I recommend setting the MTU of
176 machines behind the firewall to 1412, to allow for worst-case TCP and
177 IP options in their respective headers.
178 Normally, PPP uses the Link Control Protocol (LCP) to shut down a PPP
180 link. However, the PPPoE specification allows the link to be shut down
181 with a special PADT (PPPoE Active Discovery Terminate) packet. This
182 client recognizes this packet and will correctly terminate if a termi‐
183 nate request is received for the PPP session.
184
187 My design goals for this PPPoE client were as follows, in descending
188 order of importance:
189 o It must work.
192 o It must be a user-space program and not a kernel patch.
195 o The code must be easy to read and maintain.
198 o It must be fully compliant with RFC 2516, the proposed PPPoE
201 standard.
202 o It must never hang up forever -- if the connection is broken, it
205 must detect this and exit, allowing a wrapper script to restart
206 the connection.
207 o It must be fairly efficient.
210 I believe I have achieved all of these goals, but (of course) am open
213 to suggestions, patches and ideas. See my home page, https://di‐
214 anne.skoll.ca/projects/rp-pppoe/, for contact information.
215
218 For best results, you must give pppd an mtu option of 1492. I have ob‐
219 served problems with excessively-large frames unless I set this option.
220 Also, if pppoe is running on a firewall machine, all machines behind
221 the firewall should have MTU's of 1412.
222 If you have problems, check your system logs. pppoe logs interesting
224 things to syslog. You may have to turn on logging of debug-level mes‐
225 sages for complete diagnosis.
226
229 pppoe was written by Dianne Skoll <dianne@skoll.ca>, with much inspira‐
230 tion from an earlier version by Luke Stras.
231 The pppoe home page is https://dianne.skoll.ca/projects/rp-pppoe/.
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236 pppd(8), pppoe-sniff(8), pppoe-server(8), pppoe-relay(8)
2374th Berkeley Distribution 5 October 2015 PPPOE(8)