If you want to get connected through pppoe, perform the following steps:

Add the pppoe.lrp package to the LRP= list of packages in your Bering floppy syslinux.cfg file. The pppoe.lrp package is provided on the standard Bering floppy. Extensive documentation is available in Chapter 4, PPPoE configuration.

As explained in the pppoe documentation, download the necessary pppoe modules in /lib/modules and declare them in /etc/modules. Save modules.lrp.

Edit the adiusbadsl.conf file and set the Encapsulation parameter to 1:

(...)
Encapsulation=00000001
(...)

Backup the eagle.lrp package.

Through the leaf package configuration menu, edit the /etc/ppp/peers/dsl-provider file of the pppoe package. Add you user name as explained in the Bering pppoe documentation. Save pppoe.lrp.

Edit you /etc/interfaces file as explained above. The ppp0 section will have to modified as follows:

(...)
iface ppp0 inet ppp
        pre-up startadsl
        provider dsl-provider eth1
      post-down stopadsl
(...)

Finally adjust your Shorewall parameters as described above. You will also probably need to edit the Shorewall config file (entry 14) to adjust the CLAMPMSS variable to "yes":

(...)
# Set this variable to "Yes" or "yes" if you want the TCP "Clamp MSS to PMTU"
# option. This option is most commonly required when your internet
# interface is some variant of PPP (PPTP or PPPoE). Your kernel must
#
# If left blank, or set to "No" or "no", the option is not enabled.
# CLAMPMSS="yes"
(...)

Backup the shorwall.lrp package.