What are two reasons for using layered protocols? what is one possible disadvantage of using layered protocols?

Some of the disadvantages of using layered protocols are the redundancy and overall lower performance.
Reimplementing everything from remote and wired to connectionless and association situated application correspondence, with each ringer and shriek of BGP, MPLS, multicast steering and so on would be a gigantic endeavor and potentially unmanageable in this solid across the board convention. I could envision specialty utilize situations where most extreme execution is imperative most importantly where an exceptionally basic framework might be wanted.

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