Realms and Information Bases
To start with you need to consider how an actual routing engine works. Up to this point you only considered the Routing Policy Database (RPDB) as containing the state of the routing, more particularly the Policy Routing, structure. But this structure has several components.
Recalling the discussion of the RPDB from Chapter 3, "Linux Policy Routing Structures," the concept of the actual Routing Information Base (RIB) describes what you would call a routing structure. This RIB consists of all the elements necessary to describe how to propagate a packet based on the destination address. It contains many items of information including such details as the interface, MTU, nexthop router, TOS tag, and other information that ...
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