This topic gives in dept knowledge and carefully iterate the configuration. I will go through it once more or twice. The team really do a great Job .

Subnetting is one of the key topic and need to be carefully and deliberately learnt.

This question is not clear can you expantiate more

This Particular lesson shows that the network engineers must be deliberate in securing is network and understand what neighbor to allow and not to allowed and block every others type of solicitation/advertisement that are not related.