Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
Access control lists (ACLs) and inter-VLAN routing should not be implemented in the core layer. Because the core layer focuses on low latency and fast transport services, you should not implement mechanisms that can introduce unnecessary latency into the core layer. For example, mechanisms such as process- based switching, packet manipulation, and packet filtering introduce latency and should be avoided in the core.
The hierarchical network model divides the operation of the network into three categories:
Core layer - provides fast backbone services to the distribution layer

Distribution layer - provides policy-based access between the core and access layers

Access layer - provides physical access to the network

ACLs and inter-VLAN routing are typically implemented in the distribution layer. Because the distribution layer is focused on policy enforcement, the distribution layer provides the ideal location to implement mechanisms such as packet filtering and packet manipulation. In addition, because the distribution layer acts as an intermediary between the access layer devices and the core layer, the distribution layer is also the recommended location for route summarization and redistribution.
Because a fully meshed topology can add unnecessary cost and complexity to the design and operation of the network, a partially meshed topology is often implemented in the core layer. A fully meshed topology is not required if multiple paths exist between core layer and distribution layer devices. The core layer is particularly suited to a mesh topology because it typically contains the least number of network devices.
Fully meshed topologies restrict the scalability of a design. Hierarchical designs are intended to aid scalability, particularly in the access layer.
Quality of Service (QoS) is often implemented in all three layers of the hierarchical model. However, because the access layer provides direct connectivity to network endpoints, QoS classification and marking are typically performed in the access layer. Cisco recommends classifying and marking packets as close to the source of traffic as possible. Although classification and marking can be performed in the access layer, QoS mechanisms must be implemented in each of the higher layers for QoS to be effective.
Load balancing is often implemented in all three layers of the hierarchical model. Load balancing offers redundant paths for network traffic; the redundant paths can be used to provide bandwidth optimization and network resilience. Typically, the core and distribution layers offer a greater number of redundant paths than the access layer does. Because some devices, such as network hosts, often use only a single connection to the access layer, Cisco recommends redundant links for mission-critical endpoints, such as servers.
Reference:
Cisco: Internetwork Design Guide Internetwork Design Basics