Download the isdn.lrp package from Eric's site and store it on your Bering disquette. If you need space to do that, refer to the installation guide to learn how to do that.
Boot your Bering floppy image. Once the LEAF menu appears get access
to the linux shell by (q)uitting the menu. Edit the syslinux.cfg
file and REPLACE the pump entry by isdn in the LRP= list of packages to be
loaded at boot. Check the Bering installation guide
to learn how to do that.
Your syslinux.cfg file will then look like
(adjust to your tastes):
display syslinux.dpy timeout 0 default linux initrd=initrd.lrp init=/linuxrc rw root=/dev/ram0 boot=/dev/fd0u1680:msdos PKGPATH=/dev/fd0u1680 LRP=root,etc,local,modules,iptables,keyboard,isdn,shorwall,ulogd,dnscache,weblet
The last two lines ("default linux ... dnscache,weblet")
must be typed as a single one in syslinux.cfg