Another detail in OSPF is how node protection is handled with the multiple
areas. Consider the case where S's primary neighbor is an ABR A. Now, if
S's LFA goes to another area, that other area's path may traverse A. I
think that the other area should itself have an LFA that can protect
against the failure of A; perhaps this is sufficient?
There are two cases for this concern. The first is when the path is
diverted to the other area, as we've been discussing, but doesn't
necessarily need to come back. The second case is for an inter-area route
- where the LFA to another ABR announcing the route may not suffice because
of the path taken outside the area.
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