Off-topic, Inder Monga wrote:

Are B1, B2 or the dark colored circles the external interfaces aka the STPs?

What's an STP? :) I made a few circles red and green. I specifically did not name them. Personally, I think about red as "end point" and green as "network edge", but I did not want (or dare to) touch upon issues as if the green dot in A connecting to B is the same green dot in B connecting to A, and if network C should announce any dots in the first place (being a link without active network equipment, but with a policy; I thought of it as a transcontinental link). Also, in network virtualisation, what once was a network edge is no longer an edge in the virtualised domain. Should I still make it a green dot or not? I just picked one choice, hoping no one would ask. :) Feel free to supply your own names. STP is as good as any other name. Regards, Freek