Everytime I connect to the Internet, the 'nameserver' entries which are
originally in /etc/resolv.conf are replaced with the ones from the dialup
connection (they are restored after I hang up).
How to prevent this? I want to preserve 'nameserver 127.0.0.1' since I
serve some intranet zones on my computer.
Edit /etc/ppp/resolv/provider (if you named your connection something other
than 'provider' substitute that name). Add the line
'nameserver 127.0.0.1' to that file.
This is explained in the pppconfig man page.