auto-reconnecting lost DSL connection

Assuming you're using rp-pppoe, and have perl and ifconfig installed.

At start, configure your pppoe connection using usual pppoe-setup

Now you'll need 3 files:

1. /etc/ppp/pppoe-params (remove all "# this line must be empty", they really must be empty lines)

# this line must be empty
# this line must be empty
# this line must be empty
server
your_password
your_password
0
y
# this line must be empty

2. pppoe-reconnect.sh:

#!/bin/sh
pppoe-stop
pppoe-setup </etc/ppp/pppoe-params
pppoe-start

3. inet_reconnect.pl

#!/usr/bin/perl
use POSIX qw(setsid);

chdir '/'                 or die "Can't chdir to /: $!";
umask 0;
open STDIN, '/dev/null'   or die "Can't read /dev/null: $!";
open STDERR, '>/dev/null' or die "Can't write to /dev/null: $!";
defined(my $pid = fork)   or die "Can't fork: $!";
exit if $pid;
setsid                    or die "Can't start a new session: $!";

while(1) {
    while (!(`ifconfig` =~ /ppp0/)) {
        print "inet is down, trying to reconnect..\n";
        `pppoe-reconnect.sh`;
    }
    sleep(60);
}

Put both scripts to accessible locations (like /usr/local/sbin) and chmod +x them.
Then add inet_reconnect.pl to system startup file (I have it in /etc/conf.d/local.start in gentoo)
Done. This simple daemon will check for ppp0 in ifconfig output once per minute, and reconnect if it's not there.

And some background.. 'pppoe-setup' line in 'pppoe-reconnect.sh' may be omitted in most cases, as well as /etc/ppp/pppoe-params file. I need it because of weird behavior of our ISP's setup, so I forced to do pppoe-setup on each connect.

So, if doing simple pppoe-start is sufficient for you - just do 'pppoe-stop; pppoe-start' in reconnect script.