This script is used to as a postponed script to modify the file after the machine has been mount to AD.
This specific instance of sed, removed the first 4 lines of the kerberos file, to prevent automatic modification, then searches for DNS Fallback, and adds "Forwardable = yes" to the libdefaults section.

echo " - v0.1 ("`date`")"
# start here
sed -i old -e '1,4 d' -e 's/dns_fallback\ =\ no/dns_fallback\ =\ no\
        forwardable = yes/' /Library/Preferences/
echo " - end"
exit 0