A. when the design implements Layer 2 between the access arid distribution blocks
B. when multiple vendor devices need to be supported
C. when preempt tuning of the default gateway is needed
D. when a robust method of backing up the default gateway is needed
E. when the design implements Layer 2 between the access switch and the distribution blocks
F. when the design implements Layer 2 between the access and distribution blocks

A. OSPF stub areas can be thought of as a simple form of summarization
B. OSPF cannot filter intra area routes
C. An ARR ran only exist in two areas - the backbone and one adjacent area
D. Performance issues in the Backbone area can be offset by allowing some traffic to transit anon-backbone area
E. the size of an area （the LSDB） will be constrained by the size of the IP MTU