Ok l'ho trovato sotto il nome provider, però non c'è la stringa userpeerdns da commentare, riporto il contenuto:
# These are the options to dial out to your default service provider.
# Please customize them correctly. Only the "provider" file will be
# handled by poff and pon (unless with extra command line arguments).

# You usually need this if there is no PAP authentication
noauth

# The chat script (be sure to edit that file, too!)
connect "/usr/sbin/chat -v -f /etc/chatscripts/provider"

# Set up routing to go through this PPP link
defaultroute

# Default modem (you better replace this with /dev/ttySx!)
/dev/modem

# Speed
38400

# Keep modem up even if connection fails
persist