Disjointed Area 0 MPLS

The purpose is :
- Make R1 use MPLS to join area2 (router 3 included)
- Make R3 use backdoor to join area2 and backdoor + mpls to join Area 1
- Serial interfaces are unnumbered :

The Clue :
- Area 0 need to be extended via a virtual-link to PE4 to prevent summary lsa from area 0 to be rejected
- Virtual-link between R3 to PE5 could not be established as it's an unnumbered interface
- Without this second Vlink, R3 will prefer R2 to join R1-R2-R4 as the summary routes of area 1 received by R6 is a summary from a non-backbone area, R3 should ignore it as he is connected to backbone. The summary of area 1 received from the bacbkone is valid and installed in R3
- We need that the summary received from PE5 is also comming from backbone : We use GRE between PE5 and R3 to also extends area 0.
- Then we create a sham-link between both PE, to make routes from area 0 appears as intra-area and be prefered.
- Finally, interface serial between R2 and R3 should be configured with a low bandwidth to make tunnel the prefered routes.

Some tips :
- To prevent recursive routing with the gre, the source destination should be on the same area 2 as the tunnel itself will be on area 0 : as this we are sure source or destination will be prefered out of the tunnel as they will appear intra-area routes inside the tunnel.
-On R3 use a physical link for GRE source in order if the backdoor link goes down the tunnel will also goes down.