Campus lan and Wireless lan solution Design Guide

 
Layer-3 Routed Access 
Figure 15. 
The challenges with the routed access layer design is that the Layer 2 domains are confined to a single access 
closet, which limits flexibility for applications that require Layer 2 connectivity that extends across multiple 
access closets, the access switches must have the capability to support the Layer 3 routing functionality, and 
differences in IP addressing and subnetting must be accommodated. Many organizations have been unable to 
overcome the application requirements driving the need for Layer 2 connectivity across access-layer switches, 
resulting in the desire to address the needs using alternative designs.
Preferred Layer 2 access using a simplified distribution layer campus design 
An alternative that can handle Layer 2 access requirements and avoid the complexity of the traditional multilayer 
campus is called a Layer 2 access with simplified distribution layer design. The design uses multiple physical 
switches that act as a single logical switch, such as switch stack or Cisco StackWise Virtual Pair (SVP), or the 
less preferred single, highly-redundant physical switch. One advantage of this design is that spanning tree 
dependence is minimized, and all uplinks from the access layer to the distribution are active and passing traffic.
Even in the distributed VLAN design, you eliminate spanning tree blocked links because of looped topologies. 
You reduce dependence on spanning tree by using EtherChannel to the access layer with dual-homed uplinks. 
This is a key characteristic of this design, and you can load-balance up to eight links if needed for additional 
bandwidth. At the same time, multiple links in an EtherChannel have better performance characteristics versus 
single independent links.
 
Simplified distribution design with a VLAN per access switch 
Figure 16. 

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