Which should be performed at the core layer?

Only switching between campus (distribution) switches should be performed at the core layer. Nothing should be done to slow down forwarding of traffic, such as using ACLs, supporting clients, or routing between VLANs. Routing of data should be performed at the distribution layer of the Cisco three-tier model. Supporting clients should be done at the access layer of the Cisco three-tier model. The configuration of access should be performed at the distribution layer of the Cisco three-tier model.