Hello Georg, Aneek,
Indeed. I agree with Georg. That paragraph does not talk about OSPF hierarchy, it talks about Internet routing hierarchy where obviously OSPF would not be even running (since OSPF is an IGP protocol). The hierarchy they talk about is just an attempt to "scope" an IP address into parts that would be hierarchically related to each other, for example, something like continent->country->owner->host (just an example). With 4B IPv4 addressing, a natural approach would be to take each of the bytes for one of those hierarchical units, and that's what they talk about. We never adopted this in real life, though - the best compromise between an efficient use of IP addresses and the numbers of hierarchy is achieved by a simple approach of splitting an IP address into a network prefix and a host ID part, and allowing the network prefix to be further subnetted later on.
Attempts to make IP addressing somehow related to geographical or geopolitical reality have come in and out several times; if you check the old and already superseded IPv6 addressing documents, in particular RFCs 2373 and 2374, they talk about structuring the IPv6 address into a whole set of parts (Top-Level Aggregation, Next-Level Aggregation, Site-Level Aggregation). It never gained much popularity. Imposing strict hierarchy into IP addressing does not go well with the paradigm of getting a prefix of an arbitrary length and subnetting it further as we need.
The bottom line is - what the book says in the paragraph you quoted is about IP addressing hierarchy, not about OSPF hierarchy, and it is an old take on how we could impose certain levels of hierarchy onto IP addressing. It's not exactly what we do today, and it is not related to OSPF.
Best regards,
Peter
