Tunnels for networking are not good. We see a real-life example taking place with the twelve Thai boys that were stuck at the end of a tunnel with a very narrow section under water preventing passage. The tunnel offered them only one way out, and the particular path was not passable. This is what happens in networks. We’re thankful for the heroic rescue of these brave boys, but networks don’t always fare as well.
You will hear others speak about how a tunnel-based virtual network is the next amazing trend in networking. In fact, an analyst recently told me tunnels are great. And they are, when used for the purpose they were intended. But, using tunnels to get aggregates of packets to go where they wouldn’t go otherwise is dangerous, and will lead to the accumulation of technical debts.