Just a brief historical note to point out that there were other hierarchical node things before these, including OSPG and IS-IS; the earliest one I know of is a proposed "area" extension to the so-called 'new' ARPANet routing (I have a ref if anyone cares). If anyone knows of an earlier one, I'd be interestingin hearing of it, so I can add credits for it.
ISO-IGRP happened around/before the time of OSPF. It had a 3 level hierarchy, the lowest using system-ids, where you could get mobility like you did using IS-IS for CLNS within an area, the middle hierarchy which was a 2-byte area-id, explicitly advertised as a DV protocol, and the final level which was a longest-match prefix level which used the rest of the high-order bits of the address (the NSAP address).
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