© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Structuring and Modularizing the Network Designing the Network Hierarchy

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Layers in the Hierarchical Model

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Hierarchical Network

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Access Layer Concentration point at which clients access the network Layer 2 switching in the access layer: Defines a single broadcast domain Multilayer switching in the campus access layer: Optimally satisfies the needs of a particular user through routing, filtering, authentication, security, or quality of service Multilayer switching in the WAN access layer: Helps control WAN costs using dial-on-demand routing (DDR) and static routing

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Access Layer Connectivity in the Campus LAN Workstations are attached to VLANs with Layer 2 switches. Recommended practice: Implement one VLAN (IP subnet) per access switch. Access switches connect Layer 3 links (if only one VLAN per access switch) or via VLAN trunk. If needed, distribution routers route between VLANs.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Distribution Layer Provides multilayer switching between access and core layers: Provides media transitions Aggregates bandwidth by concentrating multiple low-speed access links into a high-speed core link Determines department or workgroup access Provides redundant connections for access devices Implements policy-based decisions: Filtering by source or destination address Filtering on input or output ports Hiding internal network numbers by route filtering Static routing Security Quality of service mechanisms

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Distribution Layer in the Routed Campus Network

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Core Layer The function of the core layer is to provide fast and efficent data transport that: Forms a high-speed backbone with fast transport services Provides redundancy and fault tolerance Offers good manageability Note: Core layer should avoid packet manipulation for filtering or access list checking.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Multilayer Switching in the Campus Core

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Routing in the WAN Network

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Summary The hierarchical network model provides a modular view of a network, making it easier to design and build a network. The purpose of the access layer is to grant end-user access to network resources. The distribution layer provides aggregation for the access layer devices and uplinks to the core layer. It is also used to enforce policy within the network. The core layer provides a high-speed, highly available backbone designed to switch packets as fast as possible.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v