Option A is correct. Creating multiple areas in OSPF can help to reduce the convergence time . This is because changes in one area do not affect other areas, so fewer routers need to run the SPF algorithm in response to a change.

Option D is correct. Creating multiple areas in OSPF can help to reduce Link State Advertisement (LSA) flooding across the network. This is because LSAs are not flooded out of their area of origin.

The two reasons for the failure to form an adjacency in a network running IS-IS could be:

B. There is no configured ISO address on any IS-IS interface. IS-IS requires each router interface to have an ISO address configured.  Without this address, the routers cannot form an adjacency 1 .

D. The family iso configuration is missing from the adjacency interface. The ‘family iso’ configuration is essential for IS-IS to function correctly.  If this configuration is missing from the adjacency interface, it could prevent the formation of an adjacency 1 .

These explanations are based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks 2 3 .