MPLS Questions

[enguy]

I would like to know some information regarding MPLS:

1. Why do we need sometimes more then 3 Labels for one packet running over MPLS network ?

2. Is it related to multipe tunnels (one in another) , and why is it needed for?

3. Is related to multiplexing of applications? And how does the multiplexing of applications work?

4. Does label stacking mean pushing the whole 32 bits header of MPLS for each label, or only the 20 bits label field?

5. Regarding Route Distinguisher - How does RD converted to a single label (RD is 26 bits while MPLS label is only 20 bits)?

6. Why does lookup process in a regular (IP) router takes longer time then in an MPLS Router?

7. Is it possible to use IPsec (Transport or Tunnel mode) over MPLS Core Network?

8. Is possible to run (encapsulate) an ATM packet over MPLS/IP Network?

Thanks in advance,