NFD

I want to clarify a point about this, about whether the cost for a prefix with CHILD_INHERIT set applies just to immediate children that don't have CAPTURE set, or all children that don't have CAPTURE set. That is, given the routes

(/,    face=1, Cost=10, `CHILD_INHERIT`=yes)
(/a,   face=1, Cost=20, `CHILD_INHERIT`=no)
(/a/b, face=2, Cost=5,  `CHILD_INHERIT`=no)

should we get

Or should we get

It seems reasonable to me that we should get the former, because we can specify a route to have CAPTURE so that inherited routes, even from all the way at the top, don't get used instead. We want to use the most efficient route possible for all prefixes, so it seems that we should pick any route that is a valid sub-prefix of the given prefix.

Reply to note-9: the first table is correct.

Formally, if we represent the RIB on a name hierarchy,
For the root node or a node that has CAPTURE on any route, the FIB entry has the same face+cost combinations as the RIB entry.
For any other node, given the FIB entry for its parent node, to compute the FIB entry for the current (child) node:

1. Clone the parent FIB entry.
2. For each route in parent RIB entry, if the route is tagged CHILD_INHERIT=no, delete the FIB nexthop record.
3. For each route in child RIB entry, if the FIB entry has a nexthop record with the same face, update this nexthop record so that the cost is the lesser between existing nexthop record and the RIB route; if the FIB entry does not have a nexthop record with the same face, add the nexthop record.

2020-03-12 NFD call decides to reject this issue.
RibMgmt rev30 reflects this choice.