Learning OpenStack Networking (Neutron) By James Denton

http://books.google.co.in/books?id=iXrKBAAAQBAJ&pg=PT194&lpg=PT194&dq=tenant+provider+external+network&source=bl&ots=IG1nzIeZ1u&sig=EpzHEdZ1kYQ98Nbzr1yqkqwmWEc&hl=en&sa=X&ei=o6BQVJXQC6XemAXSjYCoDQ&ved=0CDsQ6AEwBTgK#v=onepage&q=tenant%20provider%20external%20network&f=false