PPPOE(4) BSD Programmer's Manual PPPOE(4)
pppoe - PPP over Ethernet protocol network interface
pseudo-device pppoe
The pppoe interface encapsulates Point-to-Point Protocol (PPP) packets
inside Ethernet frames as defined by RFC 2516.
This is often used to connect a router via a DSL modem to an access con-
centrator. The pppoe interface does not by itself transmit or receive
frames, but needs an Ethernet interface to do so. This Ethernet interface
is connected to the pppoe interface via ifconfig(8). The Ethernet inter-
face needs to be marked UP, but does not need to have an IP address.
There are two basic modes of operation, controlled via the link1 switch.
The default mode, link1 not being set, tries to keep the configured ses-
sion open all the time. If the session is disconnected, a new connection
attempt is started immediately. The "dial on demand" mode, selected by
setting link1, only establishes a connection when data is being sent to
the interface.
If the kernel is compiled with option PPPOE_SERVER, there are two modes
of connection, controlled via the link0 switch. The default mode, link0
not being set, is client mode. The "PPPoE server" mode, selected by set-
ting link0, is to wait for incoming PPPoE session. This option is not set
in the GENERIC kernel and discouraged because it does not offer authenti-
cation.
Before a pppoe interface is usable, it needs to be configured. The fol-
lowing steps are necessary:
• Create the interface.
• Connect an Ethernet interface. This interface is used for the physi-
cal communication. As noted above it must be marked UP, but need not
have an IP address.
• Configure authentication. The PPP session needs to identify the
client to the peer. For more details on the available options see
spppcontrol(8).
This all is typically accomplished using an /etc/hostname.pppoe0 file.
A typical /etc/hostname.pppoe0 file looks like this:
pppoedev ne0
!/sbin/ifconfig ne0 up
!/usr/sbin/spppcontrol \$if myauthproto=pap myauthname=testcaller \
myauthkey=donttell
#!/usr/sbin/ifwatchd -d /etc/ppp/ip-down -u /etc/ppp/ip-up \$if
!/sbin/ifconfig \$if inet 0.0.0.0 0.0.0.1 netmask 0xFFFFFFFF
!/sbin/route -n add -inet default 0.0.0.1 -mtu 1446
up link2
Attention regarding the link2 option given; please read about it under
OPTIONS below before using (it is only included as the majority of users
probably does want to use this flag).
Using ifwatchd(8) may not work correctly, so it's commented out in the
example now.
Since this is a PPP interface, the addresses assigned to the interface
may change during PPP negotiation. There is no fine grained control
available for deciding which addresses are acceptable and which are not.
For the local side and the remote address there is exactly one choice:
hard coded address or wildcard. If a real address is assigned to one side
of the connection, PPP negotiation will only agree to exactly this ad-
dress. If one side is wildcarded, every address suggested by the peer
will be accepted.
To wildcard the local address set it to 0.0.0.0, to wildcard the remote
address set it to 0.0.0.1.
A pppoe enabled kernel will not interfere with other PPPoE implementa-
tions running on the same machine. Under special circumstances (details
below) this is not desirable, so the pppoe driver can be told to kill all
unknown PPPoE sessions received by the Ethernet interface used for a con-
figured pppoe interface. To do this, set the link2 flag on any interface.
Note that this will break all userland PPPoE implementations using the
same Ethernet interface! But if this Kernel PPPoE is the only implementa-
tion used, it is a useful device in case you accidentally destroy an in-
terface while a session is open; in the case of German NetDSL it can
reduce downtimes from 5 to 10 minutes down to half a minute or less.
This option is only useful if you have a static IP address assigned and
your ISP does not use LCP echo requests to monitor the link status. After
a crash or power failure the peer device still tries to send data to the
no longer active session on your computer, and might refuse to reestab-
lish a new connection, because there already is an open session. On re-
ceipt of such packets, the pppoe driver with this option set will send a
PADT packet (request to terminate the session). The peer will immediately
disconnect the orphaned session and allow a new one to be established.
hostname.if(5), ifconfig(8), ifwatchd(8), ppp(8), pppoe(8),
spppcontrol(8)
A Method for Transmitting PPP Over Ethernet (PPPoE), RFC 2516, February
1999.
http://whirlpool.net.au/wiki/adsl_theory_ppp (changing User-Agent to foo
in lynx necessary) has got an explanation how PPPoE is further encapsu-
lated on the way to your ISP and why 1446 is the optimum MTU for native
IPv4 and native IPv6 connections. Tunneled IPv6 connections using gif(4)
tunnels have an optimum MTU of 1426, the difference is just the size of
an IPv4 header for the simple encapsulation; the maximum TCP-MSS would be
1406 and 1386, respectively.
The pppoe device appeared in NetBSD 1.6 and was ported via OpenBSD 3.7 to
MirBSD #8.
This implementation is client side only.
It is important to specify "netmask 0xFFFFFFFF" to ifconfig(8). If the
netmask is unspecified, it will be set to 8 when 0.0.0.0 is configured to
the interface, and it will persist after negotiation.
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