Imagine this. Lots of machines, some virtual, some physical. Every single machine can ping every other machine, except just one pair. An administrators nightmare? Yes. Trust me, I've been there spending several hours diagnosing this particularly tricky problem.

Let's simplify the situation. Start with two Virtual Server hosts. For ease of reference, lets call them A & B. Now let's say A & B each have a two Virtual machines running on them. We'll call these C, D, E & F. C & D are running on host A, while E & F are running host B. Still with me? Maybe the annotatio