Campus lan and Wireless lan solution Design Guide

 
Traditional looped design with VLANs spanning access switches 
Figure 13. 
 
Traditional loop-free design with a VLAN per access switch 
Figure 14. 
The following is a summary of some of design and operational concerns with the traditional multilayer campus 
design, driving alternative approaches: 
● 
Spanning-tree protocol looping behavior, including blocked links, slow convergence, asymmetric 
forwarding, and switch CAM and ARP table tuning to address unicast flooding 
● 
FHRP configuration consistency, slow convergence times driving protocol tuning in conflict with non-stop 
forwarding systems 
● 
Layer 3 protocol tuning and protocol-dependent scale and recovery, multicast protocol configuration 
consistency and tuning, and general control plane, management, and forwarding complexity 
Note: 
The Flexlink+ feature of enables the user to configure a pair of a Layer 2 interfaces (trunk ports or port 
channels) where one interface is configured to act as a backup to the other. The feature provides an alternative 
solution to the Spanning Tree Protocol (STP). 
Because of the design and operational concerns inherent in the traditional multilayer campus design, 
organizations strive to deploy different designs, whenever possible. 
Layer 3 routed access campus design 
In another approach to access and distribution layer design, you can use Layer 3 beyond just the core and 
distribution layers and configure Layer 3 all the way into the access layer. Using the Layer 3 access design 
removes the Layer 2-to-Layer 3 boundary at the distribution layer, and makes each access switch the boundary 

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between the Layer 2 access ports and outbound Layer 3 connectivity. The benefits of this design are that you 
eliminate spanning tree loops and reduce protocols because the IP gateway is now the access switch. Because 
there are no spanning-tree blocking links, you can use both uplinks to the access layer and increase effective 
bandwidth available to the users. This design makes it easy to maintain configuration consistency, while 
providing excellent convergence properties with minimal tuning, as the more complex Layer 2 interaction at the 
Layer 3 distribution is eliminated.