Allow access to RackSpace database from Vagrant box
First, you want to find out what external IP address the Vagrant boxes NAT to:

What is my IP - Google

Then add an iptables rule for that IP address.

Then you will want to grant access from your MySQL database to the host (The Vagrant box)

GRANT ALL PRIVILEGES
ON database.*
TO 'user'@'vagrantboxremotehost'
IDENTIFIED BY 'password';


You can also use

TO 'user'@'%'


To allow from any IP, but that is not recommended.