Autoroute and forwarding adjacency (both covered fully in Chapter 5) rely on the fact that the tunnel head and tunnel tail are in the same area. As such, you cannot build a tunnel across multiple areas and have either autoroute or forwarding adjacency work. To put packets down an interarea tunnel, you need to use static or policy routing.
If you are taking advantage of interarea code to build intra-area tunnels (R1 to ABR1, ABR1 to ABR4, ABR3 to R4, and so on), autoroute and forwarding adjacency will work. It's only when you have a TE tunnel spanning multiple areas that autoroute and forwarding adjacency don't work.
See Chapter 5 for a more detailed explanation of how autoroute and forwarding adjacency work, and why they don't work across areas.
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