Debian dont use a rc.local file.
To create a simple rc.local equivalent in debian create a file in /etc/init.d/ called local as user root.
The file should have
and any other commands you wish to run at startup. Then make it executable:
chmod +x /etc/init.d/local
Then link the new file by running:
update-rc.d local defaults 60
You can change the last variable 60 to a lower number if you wish. The lower the number the sooner it will execute. I say 60 becuase at that point the rest of the system will be up and running. If you choose to low of a number some critical processes may not be started and dhclient wont run.
Now reboot. Whatever is in this file now will execute during bootup.
More info look at http://www.debian.org/doc/FAQ/ch-customizing.en.html