A corporate network is spread over four floors. Each floor has a Layer 2 switch and more than one VLAN. One connection from each floor leads to the basement, where all WAN connections are terminated and all servers are located. Traffic between VLANs is essential. What type of device should be used in the basement?

a multilayer switch

Explanation:

A multilayer switch -

It is a type of networking device , which can work at the higher layers of the OSI reference model , is referred to as a multilayer switch .

It helps to switch between two layers of the OSI and gives more functions on the higher OSI layers .

A multilayer can very efficiently work as a switch as well as a router at a very high speed .

Hence , from the given scenario of the question ,

The device that need to be installed in the basement is a multilayer switch .  

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.