Campus lan and Wireless lan solution Design Guide

 
Simplified distribution design with VLANs spanning access switches 
Figure 17. 
EtherChannel is a logical interface that can use a control plane protocol to manage the physical members of the 
bundle. It is better to run a dynamic channel protocol instead of using forced-on mode because a dynamic 
channel protocol performs consistency checks for interfaces programmed to be in the channel and provides 
protection to the system from inconsistent configurations. Cisco Catalyst switches provide both port 
aggregation protocol (PAgP), which is a widely deployed Cisco designed protocol, and link aggregation protocol 
(LACP), which is based on IEEE 802.3ad.
There are several other advantages to the simplified distribution layer design. You no longer need IP gateway 
redundancy protocols such as HSRP, VRRP, and GLBP, because the default IP gateway is now on a single 
logical interface and resiliency is provided by the distribution layer switch or switches. Also, the network will 
converge faster now that it is not depending on spanning tree to unblock links when a failure occurs, because 
EtherChannel provides fast sub-second failover between links in an uplink bundle.
The topology of the network from the distribution layer to the access layer is logically a hub-and-spoke 
topology, which reduces complexity of design and troubleshooting. The hub-and-spoke topology design 
provides a more efficient operation for IP Multicast in the distribution layer because there is now a single logical 
designated router to forward IP Multicast packets to a given VLAN in the access layer.
Finally, by using the single logical distribution layer design, there are fewer boxes to manage, which reduces the 
amount of time spent on ongoing provisioning and maintenance. Using the Cisco Catalyst 9000 Series switches 
for physical or logical stacking is also the basis for enabling resiliency features such as stateful switchover 
(SSO), non-stop forwarding (NSF), and in-service software upgrades (ISSU).