When designing an access layer, best practices today seem to indicate going toward a L3 design. I know the answers may be different depending on whether or not we talking about a DC design or Enterprise Campus design. Please describe when you would choose L2 over L3 in the access layer and the differences in design with DC vs. campus.
I know L2 adjacency requirements between servers such as clusters (Windows, VMWare, etc) would push for L2 in the DC access. Are there other factors too? (And if L2 is required, is it best practice is carry that L2 traffic up to the Aggregation layer and back down or just carry that L2 across directly connected trunks between access switches (i.e., build in looped squares instead of triangles). Do you keep L2 adjancies limited to just a pair of access switches so as to not increased the broadcast/collision/STP domains?
In the Enterprise campus, assuming no L2 adjacency requirements, are there any cases that would indicate a design other than L3 in the access layer?